Patent Publication Number: US-11649497-B2

Title: Methods and compositions for quantitation of proteins and RNA

Description:
RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 62/960,603, filed Jan. 13, 2020, the content of this related application is incorporated herein by reference in its entirety for all purposes. 
    
    
     REFERENCE TO SEQUENCE LISTING 
     The present application is being filed along with a Sequence Listing in electronic format. The Sequence Listing is provided as a file entitled SeqListing_68EB_298709_US, created on Jan. 12, 2021, which is 8 kilobytes in size. The information in the electronic format of the Sequence Listing is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field 
     The present disclosure relates generally to the field of molecular biology, for example identifying cells of different samples and determining protein expression profiles in cells using molecular barcoding. 
     Description of the Related Art 
     Current technology allows measurement of gene expression of single cells in a massively parallel manner (e.g., &gt;10000 cells) by attaching cell specific oligonucleotide barcodes to poly(A) mRNA molecules from individual cells as each of the cells is co-localized with a barcoded reagent bead in a compartment. Gene expression may affect protein expression. Protein-protein interaction may affect gene expression and protein expression. There is a need for systems and methods that can quantitatively analyze protein expression in cells, and simultaneously measure protein expression and gene expression in cells. 
     SUMMARY 
     Disclosed herein include methods for simultaneous measurement of protein and gene expressions in cells. In some embodiments, the method comprises: contacting a plurality of cellular component-binding reagents with a plurality of cells comprising a plurality of cellular component targets and copies of a nucleic acid target, wherein the nucleic acid target comprises mRNA, wherein each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier for the cellular component-binding reagent and a poly(A) sequence, wherein the cellular component-binding reagent specific oligonucleotide comprises DNA, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets; partitioning the plurality of cells associated with the cellular component-binding reagents to a plurality of partitions, wherein a partition of the plurality of partitions comprises a single cell from the plurality of cells associated with the cellular component-binding reagents; and in the partition comprising the single cell, contacting a plurality of oligonucleotide barcodes with the cellular component-binding reagent specific oligonucleotides and the copies of the nucleic acid target for hybridization, wherein the oligonucleotide barcodes each comprise a poly(T) sequence, a first universal sequence, and a first molecular label. The method can comprise extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended cellular component-binding reagent specific oligonucleotides each comprising a complement of the first molecular label and a complement of the first universal sequence. The method can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target to generate a plurality of barcoded nucleic acid molecules each comprising a sequence complementary to the at least a portion of the nucleic acid target and the first molecular label. The method can comprise separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended cellular component-binding reagent specific oligonucleotides. The method can comprise obtaining sequence information of the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, to determine the number of copies of at least one cellular component target of the plurality of cellular component targets in one or more of the plurality of cells. The method can comprise obtaining sequence information of the plurality of barcoded nucleic acid molecules, or products thereof, to determine the copy number of the nucleic acid target in one or more of the plurality of cells. 
     In some embodiments, separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes comprises denaturing the plurality of extended cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes. In some embodiments, separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes comprises magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a second universal sequence. 
     In some embodiments, obtaining sequence information of the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, comprises: amplifying the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof, to generate a plurality of amplified separated extended cellular component-binding reagent specific oligonucleotides; and obtaining sequencing data of the plurality of amplified separated extended cellular component-binding reagent specific oligonucleotides, or products thereof. 
     In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a second molecular label, optionally at least ten of the plurality of cellular component-binding reagent specific oligonucleotides comprise different second molecular label sequences. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and wherein the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are identical. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and wherein the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are different. In some embodiments, the number of unique first molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. In some embodiments, the number of unique second molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. In some embodiments, obtaining the sequence information comprises attaching sequencing adaptors to the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, and/or the plurality of barcoded nucleic acid molecules, or products thereof. In some embodiments, determining the copy number of the nucleic acid target in one or more of the plurality of cells comprises determining the copy number of the nucleic acid target in the plurality of cells based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of barcoded nucleic acid molecules, or products thereof. 
     The method can comprise: contacting random primers with the plurality of barcoded nucleic acid molecules, wherein each of the random primers comprises a third universal sequence, or a complement thereof, and extending the random primers hybridized to the plurality of barcoded nucleic acid molecules to generate a plurality of extension products. The method can comprise: amplifying the plurality of extension products using primers capable of hybridizing to the first universal sequence or complements thereof, and primers capable of hybridizing the third universal sequence or complements thereof, thereby generating a first plurality of barcoded amplicons. In some embodiments, amplifying the plurality of extension products comprises adding sequences of binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof, to the plurality of extension products. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the first plurality of barcoded amplicons, or products thereof. In some embodiments, determining the copy number of the nucleic acid target in the sample comprises determining the number of each of the plurality of nucleic acid targets in the sample based on the number of the first molecular labels with distinct sequences associated with barcoded amplicons of the first plurality of barcoded amplicons comprising a sequence of the each of the plurality of nucleic acid targets. In some embodiments, the sequence of the each of the plurality of nucleic acid targets comprises a subsequence of the each of the plurality of nucleic acid targets. In some embodiments, the sequence of the nucleic acid target in the first plurality of barcoded amplicons comprises a subsequence of the nucleic acid target. The method can comprise: amplifying the first plurality of barcoded amplicons using primers capable of hybridizing to the first universal sequence or complements thereof, and primers capable of hybridizing the third universal sequence or complements thereof, thereby generating a second plurality of barcoded amplicons. In some embodiments, amplifying the first plurality of barcoded amplicons comprises adding sequences of binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof, to the first plurality of barcoded amplicons. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the second plurality of barcoded amplicons, or products thereof. In some embodiments, the first plurality of barcoded amplicons and/or the second plurality of barcoded amplicons comprise whole transcriptome amplification (WTA) products. 
     The method can comprise: synthesizing a third plurality of barcoded amplicons using the plurality of barcoded nucleic acid molecules as templates to generate a third plurality of barcoded amplicons. In some embodiments, synthesizing a third plurality of barcoded amplicons comprises performing polymerase chain reaction (PCR) amplification of the plurality of the barcoded nucleic acid molecules. In some embodiments, synthesizing a third plurality of barcoded amplicons comprises PCR amplification using primers capable of hybridizing to the first universal sequence, or a complement thereof, and a target-specific primer. The method can comprise: obtaining sequence information of the third plurality of barcoded amplicons, or products thereof, and optionally obtaining the sequence information comprises attaching sequencing adaptors to the third plurality of barcoded amplicons, or products thereof. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the third plurality of barcoded amplicons, or products thereof. 
     In some embodiments, (i) amplifying the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, (ii) extending the random primers hybridized to the plurality of barcoded nucleic acid molecules to generate a plurality of extension products and/or (iii) synthesizing a third plurality of barcoded amplicons are performed separately. In some embodiments, extending the random primers hybridized to the plurality of barcoded nucleic acid molecules comprises extending the random primers hybridized to the plurality of barcoded nucleic acid molecules using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity, wherein extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes comprises extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity and/or wherein extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target comprises extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. In some embodiments, the DNA polymerase comprises a Klenow Fragment. In some embodiments, extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes comprises extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase and/or wherein extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target comprises extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target using a reverse transcriptase. In some embodiments, the reverse transcriptase comprises a viral reverse transcriptase, optionally wherein the viral reverse transcriptase is a murine leukemia virus (MLV) reverse transcriptase and/or a Moloney murine leukemia virus (MMLV) reverse transcriptase. 
     In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises an alignment sequence adjacent to the poly(dA) sequence. In some embodiments, the cellular component-binding reagent specific oligonucleotide is associated with the cellular component-binding reagent through a linker, optionally the cellular component-binding reagent specific oligonucleotide is configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the cellular component-binding reagent specific oligonucleotide from the cellular component-binding reagent, optionally dissociating the cellular component-binding reagent specific oligonucleotide and the cellular component binding reagent before contacting a plurality of oligonucleotide barcodes with the cellular component-binding reagent specific oligonucleotides. In some embodiments, the plurality of oligonucleotide barcodes are associated with a solid support, and wherein a partition of the plurality of partitions comprises a single solid support. In some embodiments, partitioning the plurality of cells comprises partitioning the plurality of cells associated with the plurality of cellular component-binding reagents and a plurality of solid supports comprising the solid support to the plurality of partitions, wherein the partition of the plurality of partitions comprises the single cell from the plurality of cells associated with the cellular component-binding reagent and the solid support, optimally wherein the partition is a well or a droplet. The method can comprise: after contacting the plurality of cellular component-binding reagents with the plurality of cells, removing one or more cellular component-binding reagents of the plurality of cellular component-binding reagents that are not contacted with the plurality of cells. In some embodiments, removing the one or more cellular component-binding reagents not contacted with the plurality of cells comprises: removing the one or more cellular component-binding reagents not contacted with the respective at least one of the plurality of cellular component targets. In some embodiments, the plurality of cells comprises T cells, B cells, tumor cells, myeloid cells, blood cells, normal cells, fetal cells, maternal cells, or a mixture thereof. 
     Disclosed herein include methods for labeling nucleic acid targets in a sample. In some embodiments, the method comprises: contacting copies of a nucleic acid target in the sample with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target, wherein the nucleic acid target comprises DNA and is associated with a cellular component binding reagent; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     Disclosed herein include methods for labeling nucleic acid targets in a sample. In some embodiments, the method comprises: contacting copies of a nucleic acid target comprising a poly(dA) sequence with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target, wherein the target-binding region comprises a poly(dT) sequence; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     In some embodiments, the nucleic acid target is associated with a cellular component binding reagent. In some embodiments, the cellular component-binding reagent is capable of specifically binding to at least one of a plurality of cellular component targets. The method can comprise: dissociating the nucleic acid target and the cellular component binding reagent. The method can comprise: dissociating the nucleic acid target and the cellular component binding reagent before contacting the copies of a nucleic acid target with the plurality of oligonucleotide barcodes. The method can comprise separating the plurality of extended nucleic acid targets from the plurality of oligonucleotide barcodes to generate a plurality of separated extended nucleic acid targets. In some embodiments, separating the plurality of extended nucleic acid targets from the plurality of oligonucleotide barcodes comprises magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of extended nucleic acid targets, or products thereof. 
     The method can comprise: amplifying the plurality of extended nucleic acid targets to generate a plurality of amplified extended nucleic acid targets, wherein determining the copy number of the nucleic acid target in the sample comprises: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of amplified extended nucleic acid targets, or products thereof. The method can comprise: amplifying the plurality of separated extended nucleic acid targets to generate a plurality of amplified separated extended nucleic acid targets, wherein determining the copy number of the nucleic acid target in the sample comprises: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of amplified separated extended nucleic acid targets, or products thereof. In some embodiments, determining the copy number of the nucleic acid target comprises determining the copy number of each of the plurality of nucleic acid targets in the sample based on the number of first molecular labels with distinct sequences associated with amplified extended nucleic acid targets of the plurality of amplified extended nucleic acid targets comprising a sequence of the each of the plurality of nucleic acid targets. In some embodiments, determining the copy number of the nucleic acid target comprises determining the copy number of each of the plurality of nucleic acid targets in the sample based on the number of first molecular labels with distinct sequences associated with amplified separated extended nucleic acid targets of the plurality of amplified extended nucleic acid targets comprising a sequence of the each of the plurality of nucleic acid targets. In some embodiments, the sequence of the each of the plurality of nucleic acid targets comprises a subsequence of the each of the plurality of nucleic acid targets. In some embodiments, the sequence of the nucleic acid target in the plurality of extended nucleic acid targets comprises a subsequence of the nucleic acid target. 
     The method can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target in the presence of a polymerase to generate a plurality of barcoded nucleic acid molecules each comprising a sequence complementary to the at least a portion of the nucleic acid target and a first molecular label. In some embodiments, extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target comprises extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target using a reverse transcriptase. In some embodiments, extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target comprises extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. In some embodiments, extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes comprises extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. In some embodiments, the DNA polymerase comprises a Klenow Fragment. In some embodiments, extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes comprises extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase. In some embodiments, the reverse transcriptase comprises a viral reverse transcriptase. In some embodiments, the viral reverse transcriptase is a murine leukemia virus (MLV) reverse transcriptase. In some embodiments, the viral reverse transcriptase is a Moloney murine leukemia virus (MMLV) reverse transcriptase. In some embodiments, the step of extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target and the step of extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target are performed simultaneously. 
     In some embodiments, the target-binding region comprises a poly(dT) sequence. In some embodiments, the nucleic acid target comprises a poly(dA) sequence. In some embodiments, the nucleic acid target comprises an alignment sequence adjacent to the poly(dA) sequence. In some embodiments, the nucleic acid target is associated with the cellular component-binding reagent through a linker. In some embodiments, the nucleic acid target is configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the nucleic acid target from the cellular component-binding reagent. In some embodiments, the plurality of extended nucleic acid targets comprises barcoded deoxyribonucleic acid (DNA) molecules. In some embodiments, the nucleic acid target comprises a nucleic acid molecule. In some embodiments, the nucleic acid molecule comprises ribonucleic acid (RNA), messenger RNA (mRNA), microRNA, small interfering RNA (siRNA), RNA degradation product, RNA comprising a poly(A) tail, or any combination thereof. In some embodiments, the nucleic acid target comprises a sample indexing oligonucleotide, and optionally the sample indexing oligonucleotide comprises a sample indexing sequence, and sample indexing sequences of at least two sample indexing compositions of a plurality of sample indexing compositions comprise different sequences. In some embodiments, the nucleic acid target comprises a cellular component-binding reagent specific oligonucleotide. 
     In some embodiments, a cellular component-binding reagent specific oligonucleotide comprises a unique identifier sequence for the cellular component-binding reagent. In some embodiments, each oligonucleotide barcode comprises a first universal sequence. In some embodiments, plurality of extended nucleic acid targets comprise a complement of the first universal sequence. In some embodiments, amplifying the plurality of extended nucleic acid targets and/or amplifying the plurality of separated extended nucleic acid targets comprises using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and an amplification primer. In some embodiments, the amplification primer is a target-specific primer. In some embodiments, the nucleic acid target comprises a second universal sequence. In some embodiments, amplifying the plurality of extended nucleic acid targets and/or amplifying the plurality of separated extended nucleic acid targets comprises using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof. The method can comprise: obtaining sequence information of the plurality of extended nucleic acid molecules, or products thereof. In some embodiments, obtaining the sequence information comprises attaching sequencing adaptors to the plurality of extended nucleic acid targets, or products thereof. In some embodiments, the sample comprises a single cell, a plurality of cells, a plurality of single cells, a tissue, a tumor sample, or any combination thereof. 
     Disclosed herein include methods for sample identification. In some embodiments, the method comprises: contacting each of a plurality of samples with a sample indexing composition of a plurality of sample indexing compositions, respectively, wherein each of the plurality of samples comprises one or more cells each comprising one or more cellular component targets, wherein the sample indexing composition comprises a cellular component-binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component-binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences. The method can comprise contacting the sample indexing oligonucleotides of the plurality of sample indexing compositions with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the sample indexing oligonucleotide. The method can comprise extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended sample indexing oligonucleotides each comprising a complement of the first molecular label. The method can comprise denaturing the plurality of extended sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes. The method can comprise obtaining sequencing data of the plurality of extended sample indexing oligonucleotides, or products thereof. The method can comprise identifying the sample origin of at least one cell of the plurality of cells based on the sample indexing sequence of at least one extended sample indexing oligonucleotide, or product thereof, of the plurality of extended sample indexing oligonucleotides, or products thereof, in the sequencing data. 
     The method can comprise separating the plurality of extended sample indexing oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended sample indexing oligonucleotides. In some embodiments, separating the plurality of extended sample indexing oligonucleotides from the plurality of oligonucleotide barcodes comprises magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. In some embodiments, each oligonucleotide barcode comprises a first universal sequence. In some embodiments, the plurality of extended sample indexing oligonucleotides comprise a complement of the first universal sequence. In some embodiments, the sample indexing oligonucleotide comprises a second molecular label. In some embodiments, the second molecular label sequences of at least two sample indexing oligonucleotides are different, and wherein the sample indexing sequences of the at least two sample indexing oligonucleotides are identical. In some embodiments, the second molecular label sequences of at least two sample indexing oligonucleotides are different, and wherein the sample indexing sequences of the at least two sample indexing oligonucleotides are different. In some embodiments, sample indexing sequences of at least 10, 100, or 1000 sample indexing compositions of the plurality of sample indexing compositions comprise different sequences. In some embodiments, the sample indexing oligonucleotide comprises a second universal sequence. 
     In some embodiments, identifying the sample origin of the at least one cell comprises identifying the presence or absence of the sample indexing sequence of at least one extended sample indexing oligonucleotide, or product thereof, in the sequencing data. In some embodiments, identifying the presence or absence of the sample indexing sequence comprises: amplifying the at least one extended sample indexing oligonucleotides, or products thereof, using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof, to generate a plurality of amplified extended sample indexing oligonucleotides; obtaining sequencing data of the plurality of amplified extended sample indexing oligonucleotides, or products thereof, and identifying the sample origin of the cell based on the sample indexing sequence of an amplified extended sample indexing oligonucleotide, or product thereof, of the plurality of amplified extended sample indexing oligonucleotides, or products thereof, that correspond to the at least one extended sample indexing oligonucleotide, or product thereof, in the sequencing data. 
     In some embodiments, amplifying the at least one extended sample indexing oligonucleotides, or products thereof, comprises attaching sequencing adaptors to the plurality of extended sample indexing oligonucleotides, or products thereof. In some embodiments, extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes comprises extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase. In some embodiments, extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes comprises extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. In some embodiments, the DNA polymerase comprises a Klenow Fragment. 
     The method can comprise: removing unbound sample indexing compositions of the plurality of sample indexing compositions. In some embodiments, removing the unbound sample indexing compositions comprises washing the one or more cells from each of the plurality of samples with a washing buffer. In some embodiments, removing the unbound sample indexing compositions comprises selecting cells bound to at least one cellular component-binding reagent using flow cytometry. In some embodiments, the sample indexing oligonucleotide is configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the sample indexing oligonucleotide from the cellular component-binding reagent. In some embodiments, the target-binding region comprises a poly(dT) sequence. In some embodiments, the sample indexing oligonucleotide comprises a poly(dA) region. In some embodiments, the sample indexing oligonucleotide comprises an alignment sequence adjacent to the poly(dA) region. In some embodiments, the sample indexing oligonucleotide is associated with the cellular component-binding reagent through a linker. In some embodiments, a sample of the plurality of samples comprises a plurality of cells, a plurality of single cells, a tissue, a tumor sample, or any combination thereof. 
     Disclosed herein include methods for measuring cellular component expression in cells. In some embodiments, the method comprises: contacting a plurality of cellular component-binding reagents with a plurality of cells comprising a plurality of cellular component targets, wherein each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier sequence for the cellular component-binding reagent, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets; and contacting the cellular component-binding reagent specific oligonucleotides with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the cellular component-binding reagent specific oligonucleotide. The method can comprise extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended cellular component-binding reagent specific oligonucleotides each comprising a complement of the first molecular label. The method can comprise denaturing the plurality of extended cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes. The method can comprise obtaining sequence information of the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, to determine the number of copies of at least one cellular component target of the plurality of cellular component targets in one or more of the plurality of cells. 
     The method can comprise: prior to extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes: partitioning the plurality of cells associated with the plurality of cellular component-binding reagents to a plurality of partitions, wherein a partition of the plurality of partitions comprises a single cell from the plurality of cells associated with the cellular component-binding reagents; in the partition comprising the single cell, contacting the cellular component-binding reagent specific oligonucleotides with the plurality of oligonucleotide barcodes. In some embodiments, the plurality of oligonucleotide barcodes are associated with a solid support, and wherein a partition of the plurality of partitions comprises a single solid support. The method can comprise separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended cellular component-binding reagent specific oligonucleotides. In some embodiments, separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes comprises magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. 
     In some embodiments, each oligonucleotide barcode comprises a first universal sequence. In some embodiments, the plurality of extended cellular component-binding reagent specific oligonucleotides comprise a complement of the first universal sequence. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a second universal sequence. In some embodiments, obtaining sequence information of the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, comprises: amplifying the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof, to generate a plurality of amplified extended cellular component-binding reagent specific oligonucleotides; and obtaining sequencing data of the plurality of amplified extended cellular component-binding reagent specific oligonucleotides, or products thereof. 
     In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a second molecular label. In some embodiments, at least ten of the plurality of cellular component-binding reagent specific oligonucleotides comprise different second molecular label sequences. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and wherein the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are identical. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and wherein the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are different. In some embodiments, the number of unique first molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. In some embodiments, the number of unique second molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. 
     In some embodiments, obtaining the sequence information comprises attaching sequencing adaptors to the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof. In some embodiments, extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes comprises extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase. In some embodiments, extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes comprises extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. In some embodiments, the DNA polymerase comprises a Klenow Fragment. 
     In some embodiments, the target-binding region comprises a poly(dT) sequence. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a poly(dA) region, optionally the cellular component-binding reagent specific oligonucleotide comprises an alignment sequence adjacent to the poly(dA) region. In some embodiments, the cellular component-binding reagent specific oligonucleotide is associated with the cellular component-binding reagent through a linker. In some embodiments, the cellular component-binding reagent specific oligonucleotide is configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the cellular component-binding reagent specific oligonucleotide from the cellular component-binding reagent. In some embodiments, partitioning the plurality of cells comprises partitioning the plurality of cells associated with the plurality of cellular component-binding reagents and a plurality of solid supports comprising the solid support to the plurality of partitions, wherein the partition of the plurality of partitions comprises the single cell from the plurality of cells associated with the cellular component-binding reagent and the solid support. In some embodiments, the partition is a well or a droplet. The method can comprise: after contacting the plurality of cellular component-binding reagents with the plurality of cells, removing one or more cellular component-binding reagents of the plurality of cellular component-binding reagents that are not contacted with the plurality of cells. In some embodiments, removing the one or more cellular component-binding reagents not contacted with the plurality of cells comprises: removing the one or more cellular component-binding reagents not contacted with the respective at least one of the plurality of cellular component targets. In some embodiments, the plurality of cells comprises T cells, B cells, tumor cells, myeloid cells, blood cells, normal cells, fetal cells, maternal cells, or a mixture thereof. In some embodiments, denaturing comprises heating and/or alkaline denaturation. 
     In some embodiments, the first universal sequence, the second universal sequence, and/or the third universal sequence are the same. In some embodiments, the first universal sequence, the second universal sequence, and/or the third universal sequence are different. In some embodiments, the first universal sequence, the second universal sequence, and/or the third universal sequence comprise the binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof. In some embodiments, the sequencing adaptors comprise a P5 sequence, a P7 sequence, complementary sequences thereof, and/or portions thereof. In some embodiments, the sequencing primers comprise a Read 1 sequencing primer, a Read 2 sequencing primer, complementary sequences thereof, and/or portions thereof. In some embodiments, the alignment sequence is one or more nucleotides in length, or two or more nucleotides in length. In some embodiments, (a) the alignment sequence comprises a guanine, a cytosine, a thymine, a uracil, or a combination thereof, (b) the alignment sequence comprises a poly(dT) sequence, a poly(dG) sequence, a poly(dC) sequence, a poly(dU) sequence, or a combination thereof; and/or (c) the alignment sequence is 5′ to the poly(dA) region. In some embodiments, the linker comprises a carbon chain, optionally the carbon chain comprises 2-30 carbons, and further optionally the carbon chain comprises 12 carbons. In some embodiments, the linker comprises 5′ amino modifier C12 (5AmMC12), or a derivative thereof. In some embodiments, the cellular component target comprises a protein target. In some embodiments, the cellular component target comprises a carbohydrate, a lipid, a protein, an extracellular protein, a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, a major histocompatibility complex, a tumor antigen, a receptor, an intracellular protein, or any combination thereof. In some embodiments, the cellular component target is on a cell surface. In some embodiments, at least 10 of the plurality of oligonucleotide barcodes comprise different first molecular label sequences. In some embodiments, the plurality of oligonucleotide barcodes are associated with a solid support. In some embodiments, the plurality of oligonucleotide barcodes each comprise a cell label. In some embodiments, each cell label of the plurality of oligonucleotide barcodes comprises at least 6 nucleotides. In some embodiments, oligonucleotide barcodes associated with the same solid support comprise the same cell label. In some embodiments, oligonucleotide barcodes associated with different solid supports comprise different cell labels. 
     In some embodiments, the solid support comprises a synthetic particle. In some embodiments, the solid support comprises a planar surface. In some embodiments, the sample comprises a single cell, the method comprising associating a synthetic particle comprising the plurality of the oligonucleotide barcodes with the single cell in the sample. In some embodiments, the synthetic particle and the single cell are in the same partition, and optionally the partition is a well or a droplet. In some embodiments, at least one of the plurality of oligonucleotide barcodes is immobilized on, partially immobilized, enclosed in, or partially enclosed in the synthetic particle. In some embodiments, the synthetic particle is disruptable. In some embodiments, the synthetic particle comprises a bead. In some embodiments, the bead comprises a Sepharose bead, a streptavidin bead, an agarose bead, a magnetic bead, a conjugated bead, a protein A conjugated bead, a protein G conjugated bead, a protein A/G conjugated bead, a protein L conjugated bead, an oligo(dT) conjugated bead, a silica bead, a silica-like bead, an anti-biotin microbead, an anti-fluorochrome microbead, or any combination thereof. In some embodiments, the synthetic particle comprises a material selected from the group consisting of polydimethylsiloxane (PDMS), polystyrene, glass, polypropylene, agarose, gelatin, hydrogel, paramagnetic, ceramic, plastic, glass, methylstyrene, acrylic polymer, titanium, latex, Sepharose, cellulose, nylon, silicone, and any combination thereof. In some embodiments, the synthetic particle comprises a disruptable hydrogel particle. 
    
    
     
       BRIEF DESCRIPTION OF TIE DRAWINGS 
         FIG.  1    illustrates a non-limiting exemplary stochastic barcode. 
         FIG.  2    shows a non-limiting exemplary workflow of stochastic barcoding and digital counting. 
         FIG.  3    is a schematic illustration showing a non-limiting exemplary process for generating an indexed library of the stochastically barcoded targets from a plurality of targets. 
         FIG.  4    shows a schematic illustration of an exemplary protein binding reagent (antibody illustrated here) associated with an oligonucleotide comprising a unique identifier for the protein binding reagent. 
         FIG.  5    shows a schematic illustration of an exemplary binding reagent (antibody illustrated here) associated with an oligonucleotide comprising a unique identifier for sample indexing to determine cells from the same or different samples. 
         FIG.  6    shows a schematic illustration of an exemplary workflow of using oligonucleotide-associated antibodies to determine cellular component expression (e.g., protein expression) and gene expression simultaneously in a high throughput manner. 
         FIG.  7    shows a schematic illustration of an exemplary workflow of using oligonucleotide-associated antibodies for sample indexing. 
         FIG.  8    shows a schematic illustration of a non-limiting exemplary workflow of barcoding of a binding reagent oligonucleotide (antibody oligonucleotide illustrated here) that is associated with a binding reagent (antibody illustrated here). 
         FIGS.  9 A- 9 D  show non-limiting exemplary designs of oligonucleotides for determining protein expression and gene expression simultaneously and for sample indexing. 
         FIG.  10    shows a schematic illustration of a non-limiting exemplary oligonucleotide sequence for determining protein expression and gene expression simultaneously and for sample indexing. 
         FIGS.  11 A- 11 B  show non-limiting exemplary designs of oligonucleotides for determining protein expression and gene expression simultaneously and for sample indexing. 
         FIG.  12    shows a non-limiting exemplary workflow of separate PCR workflows for protein quantitation and RNA quantitation. 
         FIG.  13 A  shows schematic illustrations of non-limiting exemplary compositions for labeling nucleic acid targets. 
         FIG.  13 B  shows schematic illustrations of non-limiting exemplary sequences and complements attached to the bead after extension (e.g., reverse transcription) according to the methods and compositions provided herein. 
         FIG.  13 C  shows schematic illustrations of non-limiting soluble material that can be denatured off after extension (e.g., reverse transcription) according to the methods and compositions provided herein. 
         FIGS.  14 A- 14 C  show schematic illustrations of non-limiting exemplary workflows for labeling nucleic acid targets. 
         FIGS.  15 A- 15 D  show schematic illustrations of non-limiting exemplary workflows for simultaneous measurement of protein and gene expressions in cells. 
         FIGS.  16 - 17    provide non-limiting exemplary workflows for the methods provided herein. 
         FIGS.  18 A- 18 B  depict an exemplary Sample Bioanalyzer High Sensitivity DNA trace of RPE PCR product ( FIG.  18 A ) and an exemplary Sample TapeStation High Sensitivity D5000 trace of RPE PCR product. 
         FIGS.  19 A- 19 B  depict an exemplary Sample Bioanalyzer High Sensitivity DNA trace of WTA Index PCR product ( FIG.  19 A ) and an exemplary Sample TapeStation High Sensitivity D5000 trace of WTA Index PCR product. 
         FIG.  20    depicts an exemplary sample bioanalyzer high-sensitivity DNA trace for an Index PCR product with an observable peak at 165 bp. 
         FIG.  21    depicts workflow for the experimental conditions tested. 
         FIGS.  22 A- 22 H  depict PCR1 traces of conditions Control mRNA ( FIG.  22 A ), Control Ab-oligo ( FIG.  22 B ), On Bead A mRNA ( FIG.  22 C ), On Bead A Ab-oligo ( FIG.  22 D ), Sup A ( FIG.  22 E ), On Bead B mRNA ( FIG.  22 F ), On Bead B “junk” ( FIG.  22 G ), and Sup B ( FIG.  22 H ). 
         FIGS.  23 A- 23 B  depict PCR1 overlays of conditions Ctrl mRNA, On Bead A mRNA, and On Bead B mRNA ( FIG.  23 A ), and PCR1 overlays of conditions Ctrl Ab-oligo, On Bead A Ab-oligo, Supernatant A, and Supernatant B ( FIG.  23 B ). 
         FIGS.  24 A- 24 C  depict mRNA PCR2 Traces of condition Control mRNA ( FIG.  24 A ), On Bead A mRNA ( FIG.  24 B ), and On Bead B mRNA ( FIG.  24 C ). 
         FIG.  25    depicts mRNA PCR2 Overlay of Ctrl mRNA, On Bead A mRNA, and On Bead B mRNA. 
         FIGS.  26 A- 26 C  depicts mRNA Index PCR Traces of conditions Control mRNA ( FIG.  26 A ), On Bead A mRNA ( FIG.  26 B ), and On Bead B mRNA ( FIG.  26 C ). 
         FIG.  27    depicts an mRNA Index PCR Overlay of conditions Ctrl mRNA, On Bead A mRNA, and On Bead B mRNA. 
         FIGS.  28 A- 28 D  depict AbO Index PCR Traces of conditions Control Ab-oligo ( FIG.  28 A ), On Bead A Ab-oligo ( FIG.  28 B ), Sup A ( FIG.  28 C ), and Sup B ( FIG.  28 D ). 
         FIG.  29    depicts an AbO Index PCR Overlay of Ctrl Ab-oligo, On Bead A Ab-oligo, Sup A, and Sup B. 
         FIGS.  30 A- 30 B  depict sequencing metrics of down-sampled libraries.  FIG.  30 A  depicts exemplary data related to the ABC metrics, AbSeq sensitivity, and AbSeq sequencing saturation of Ctrl, OnBeadA, SupA, and SupB.  FIG.  30 B  depicts exemplary data related to the mRNA metrics, mRNA sensitivity, and mRNA sequencing saturation of Ctrl, OnBeadA, and OnBeadB. 
         FIGS.  31 A- 31 B  depict exemplary data related to proxy oligonucleotide sensitivity. 
         FIGS.  32 A- 32 D  depict proxy oligo detection correlation analysis of Ctrl versus SupA ( FIG.  32 A ), Ctrl versus OnBeadA ( FIG.  32 B ), Ctrl versus SupB ( FIG.  32 C ), and SupA versus SupB ( FIG.  32 D ). 
         FIGS.  33 A- 33 G  depict noise gating (cell signal to non-cell noise) analysis of the data provided herein. Noise gating analysis is depicted for conditions Ctrl ( FIG.  33 A ), OnBeadA ( FIG.  33 B ), SupA ( FIG.  33 C ), and SupB ( FIG.  33 D ). Cell labels per gate (relative to Ctrl) and protein labels per gate (relative to Ctrl) are shown in  FIGS.  33 E and  33 F , respectively.  FIG.  33 G  depicts a non-limiting exemplary noise gating of the combined data. 
         FIGS.  34 A- 34 J  depict the results of mRNA sensitivity analysis.  FIG.  34 A  depicts a heat map of the top 25% of genes detected in the panel. Clustering and correlation analysis of the Ctrl versus OnBeadA ( FIGS.  34 B- 34 D ), Ctrl versus OnBeadB ( FIGS.  34 E- 34 G ), and OnBeadA versus OnBeadB ( FIGS.  34 E- 34 G ) conditions are shown. 
         FIGS.  35 A- 35 D  depict analysis of noise per oligo in different gates for the conditions Ctrl ( FIG.  35 A ), SupA ( FIG.  35 B ), SupB ( FIG.  35 C ), and On Bead ( FIG.  35 D ). 
         FIG.  36    depicts a Cell Label comparison B versus cell gate. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein and made part of the disclosure herein. 
     All patents, published patent applications, other publications, and sequences from GenBank, and other databases referred to herein are incorporated by reference in their entirety with respect to the related technology. 
     Quantifying small numbers of nucleic acids, for example messenger ribonucleotide acid (mRNA) molecules, is clinically important for determining, for example, the genes that are expressed in a cell at different stages of development or under different environmental conditions. However, it can also be very challenging to determine the absolute number of nucleic acid molecules (e.g., mRNA molecules), especially when the number of molecules is very small. One method to determine the absolute number of molecules in a sample is digital polymerase chain reaction (PCR). Ideally, PCR produces an identical copy of a molecule at each cycle. However, PCR can have disadvantages such that each molecule replicates with a stochastic probability, and this probability varies by PCR cycle and gene sequence, resulting in amplification bias and inaccurate gene expression measurements. Stochastic barcodes with unique molecular labels (also referred to as molecular indexes (MIs)) can be used to count the number of molecules and correct for amplification bias. Stochastic barcoding such as the Precise™ assay (Cellular Research, Inc. (Palo Alto, Calif.)) can correct for bias induced by PCR and library preparation steps by using molecular labels (MLs) to label mRNAs during reverse transcription (RT). 
     The Precise™ assay can utilize a non-depleting pool of stochastic barcodes with large number, for example 6561 to 65536, unique molecular labels on poly(T) oligonucleotides to hybridize to all poly(A)-mRNAs in a sample during the RT step. A stochastic barcode can comprise a universal PCR priming site. During RT, target gene molecules react randomly with stochastic barcodes. Each target molecule can hybridize to a stochastic barcode resulting to generate stochastically barcoded complementary ribonucleotide acid (cDNA) molecules). After labeling, stochastically barcoded cDNA molecules from microwells of a microwell plate can be pooled into a single tube for PCR amplification and sequencing. Raw sequencing data can be analyzed to produce the number of reads, the number of stochastic barcodes with unique molecular labels, and the numbers of mRNA molecules. 
     Methods for determining mRNA expression profiles of single cells can be performed in a massively parallel manner. For example, the Precise™ assay can be used to determine the mRNA expression profiles of more than 10000 cells simultaneously. The number of single cells (e.g., 100s or 1000s of singles) for analysis per sample can be lower than the capacity of the current single cell technology. Pooling of cells from different samples enables improved utilization of the capacity of the current single technology, thus lowering reagents wasted and the cost of single cell analysis. The disclosure provides methods of sample indexing for distinguishing cells of different samples for cDNA library preparation for cell analysis, such as single cell analysis. Pooling of cells from different samples can minimize the variations in cDNA library preparation of cells of different samples, thus enabling more accurate comparisons of different samples. 
     Disclosed herein include methods for simultaneous measurement of protein and gene expressions in cells. In some embodiments, the method comprises: contacting a plurality of cellular component-binding reagents with a plurality of cells comprising a plurality of cellular component targets and copies of a nucleic acid target, wherein the nucleic acid target comprises mRNA, wherein each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier for the cellular component-binding reagent and a poly(A) sequence, wherein the cellular component-binding reagent specific oligonucleotide comprises DNA, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets; partitioning the plurality of cells associated with the cellular component-binding reagents to a plurality of partitions, wherein a partition of the plurality of partitions comprises a single cell from the plurality of cells associated with the cellular component-binding reagents; and in the partition comprising the single cell, contacting a plurality of oligonucleotide barcodes with the cellular component-binding reagent specific oligonucleotides and the copies of the nucleic acid target for hybridization, wherein the oligonucleotide barcodes each comprise a poly(T) sequence, a first universal sequence, and a first molecular label. The method can comprise extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended cellular component-binding reagent specific oligonucleotides each comprising a complement of the first molecular label and a complement of the first universal sequence. The method can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target to generate a plurality of barcoded nucleic acid molecules each comprising a sequence complementary to the at least a portion of the nucleic acid target and the first molecular label. The method can comprise separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended cellular component-binding reagent specific oligonucleotides. The method can comprise obtaining sequence information of the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, to determine the number of copies of at least one cellular component target of the plurality of cellular component targets in one or more of the plurality of cells. The method can comprise obtaining sequence information of the plurality of barcoded nucleic acid molecules, or products thereof, to determine the copy number of the nucleic acid target in one or more of the plurality of cells. 
     Disclosed herein include methods for labeling nucleic acid targets in a sample. In some embodiments, the method comprises: contacting copies of a nucleic acid target in the sample with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target, wherein the nucleic acid target comprises DNA and is associated with a cellular component binding reagent; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     Disclosed herein include methods for labeling nucleic acid targets in a sample. In some embodiments, the method comprises: contacting copies of a nucleic acid target comprising a poly(dA) sequence with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target, wherein the target-binding region comprises a poly(dT) sequence; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     Disclosed herein include methods for sample identification. In some embodiments, the method comprises: contacting each of a plurality of samples with a sample indexing composition of a plurality of sample indexing compositions, respectively, wherein each of the plurality of samples comprises one or more cells each comprising one or more cellular component targets, wherein the sample indexing composition comprises a cellular component-binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component-binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences. The method can comprise contacting the sample indexing oligonucleotides of the plurality of sample indexing compositions with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the sample indexing oligonucleotide. The method can comprise extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended sample indexing oligonucleotides each comprising a complement of the first molecular label. The method can comprise denaturing the plurality of extended sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes. The method can comprise obtaining sequencing data of the plurality of extended sample indexing oligonucleotides, or products thereof. The method can comprise identifying the sample origin of at least one cell of the plurality of cells based on the sample indexing sequence of at least one extended sample indexing oligonucleotide, or product thereof, of the plurality of extended sample indexing oligonucleotides, or products thereof, in the sequencing data. 
     Disclosed herein include methods for measuring cellular component expression in cells. In some embodiments, the method comprises: contacting a plurality of cellular component-binding reagents with a plurality of cells comprising a plurality of cellular component targets, wherein each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier sequence for the cellular component-binding reagent, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets; and contacting the cellular component-binding reagent specific oligonucleotides with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the cellular component-binding reagent specific oligonucleotide. The method can comprise extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended cellular component-binding reagent specific oligonucleotides each comprising a complement of the first molecular label. The method can comprise denaturing the plurality of extended cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes. The method can comprise obtaining sequence information of the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, to determine the number of copies of at least one cellular component target of the plurality of cellular component targets in one or more of the plurality of cells. 
     Definitions 
     Unless defined otherwise, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure belongs. See, e.g., Singleton et al., Dictionary of Microbiology and Molecular Biology 2nd ed., J. Wiley &amp; Sons (New York, N.Y. 1994); Sambrook et al., Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Press (Cold Spring Harbor, N.Y. 1989). For purposes of the present disclosure, the following terms are defined below. 
     As used herein, the term “adaptor” can mean a sequence to facilitate amplification or sequencing of associated nucleic acids. The associated nucleic acids can comprise target nucleic acids. The associated nucleic acids can comprise one or more of spatial labels, target labels, sample labels, indexing label, or barcode sequences (e.g., molecular labels). The adapters can be linear. The adaptors can be pre-adenylated adapters. The adaptors can be double- or single-stranded. One or more adaptor can be located on the 5′ or 3′ end of a nucleic acid. When the adaptors comprise known sequences on the 5′ and 3′ ends, the known sequences can be the same or different sequences. An adaptor located on the 5′ and/or 3′ ends of a polynucleotide can be capable of hybridizing to one or more oligonucleotides immobilized on a surface. An adapter can, in some embodiments, comprise a universal sequence. A universal sequence can be a region of nucleotide sequence that is common to two or more nucleic acid molecules. The two or more nucleic acid molecules can also have regions of different sequence. Thus, for example, the 5′ adapters can comprise identical and/or universal nucleic acid sequences and the 3′ adapters can comprise identical and/or universal sequences. A universal sequence that may be present in different members of a plurality of nucleic acid molecules can allow the replication or amplification of multiple different sequences using a single universal primer that is complementary to the universal sequence. Similarly, at least one, two (e.g., a pair) or more universal sequences that may be present in different members of a collection of nucleic acid molecules can allow the replication or amplification of multiple different sequences using at least one, two (e.g., a pair) or more single universal primers that are complementary to the universal sequences. Thus, a universal primer includes a sequence that can hybridize to such a universal sequence. The target nucleic acid sequence-bearing molecules may be modified to attach universal adapters (e.g., non-target nucleic acid sequences) to one or both ends of the different target nucleic acid sequences. The one or more universal primers attached to the target nucleic acid can provide sites for hybridization of universal primers. The one or more universal primers attached to the target nucleic acid can be the same or different from each other. 
     As used herein, an antibody can be a full-length (e.g., naturally occurring or formed by normal immunoglobulin gene fragment recombinatorial processes) immunoglobulin molecule (e.g., an IgG antibody) or an immunologically active (i.e., specifically binding) portion of an immunoglobulin molecule, like an antibody fragment. 
     In some embodiments, an antibody is a functional antibody fragment. For example, an antibody fragment can be a portion of an antibody such as F(ab′)2, Fab′, Fab, Fv, sFv and the like. An antibody fragment can bind with the same antigen that is recognized by the full-length antibody. An antibody fragment can include isolated fragments consisting of the variable regions of antibodies, such as the “Fv” fragments consisting of the variable regions of the heavy and light chains and recombinant single chain polypeptide molecules in which light and heavy variable regions are connected by a peptide linker (“scFv proteins”). Exemplary antibodies can include, but are not limited to, antibodies for cancer cells, antibodies for viruses, antibodies that bind to cell surface receptors (for example, CD8, CD34, and CD45), and therapeutic antibodies. 
     As used herein the term “associated” or “associated with” can mean that two or more species are identifiable as being co-located at a point in time. An association can mean that two or more species are or were within a similar container. An association can be an informatics association. For example, digital information regarding two or more species can be stored and can be used to determine that one or more of the species were co-located at a point in time. An association can also be a physical association. In some embodiments, two or more associated species are “tethered”, “attached”, or “immobilized” to one another or to a common solid or semisolid surface. An association may refer to covalent or non-covalent means for attaching labels to solid or semi-solid supports such as beads. An association may be a covalent bond between a target and a label. An association can comprise hybridization between two molecules (such as a target molecule and a label). 
     As used herein, the term “complementary” can refer to the capacity for precise pairing between two nucleotides. For example, if a nucleotide at a given position of a nucleic acid is capable of hydrogen bonding with a nucleotide of another nucleic acid, then the two nucleic acids are considered to be complementary to one another at that position. Complementarity between two single-stranded nucleic acid molecules may be “partial,” in which only some of the nucleotides bind, or it may be complete when total complementarity exists between the single-stranded molecules. A first nucleotide sequence can be said to be the “complement” of a second sequence if the first nucleotide sequence is complementary to the second nucleotide sequence. A first nucleotide sequence can be said to be the “reverse complement” of a second sequence, if the first nucleotide sequence is complementary to a sequence that is the reverse (i.e., the order of the nucleotides is reversed) of the second sequence. As used herein, the terms “complement”, “complementary”, and “reverse complement” can be used interchangeably. It is understood from the disclosure that if a molecule can hybridize to another molecule it may be the complement of the molecule that is hybridizing. 
     As used herein, the term “digital counting” can refer to a method for estimating a number of target molecules in a sample. Digital counting can include the step of determining a number of unique labels that have been associated with targets in a sample. This methodology, which can be stochastic in nature, transforms the problem of counting molecules from one of locating and identifying identical molecules to a series of yes/no digital questions regarding detection of a set of predefined labels. 
     As used herein, the term “label” or “labels” can refer to nucleic acid codes associated with a target within a sample. A label can be, for example, a nucleic acid label. A label can be an entirely or partially amplifiable label. A label can be entirely or partially sequencable label. A label can be a portion of a native nucleic acid that is identifiable as distinct. A label can be a known sequence. A label can comprise a junction of nucleic acid sequences, for example a junction of a native and non-native sequence. As used herein, the term “label” can be used interchangeably with the terms, “index”, “tag,” or “label-tag.” Labels can convey information. For example, in various embodiments, labels can be used to determine an identity of a sample, a source of a sample, an identity of a cell, and/or a target. 
     As used herein, the term “non-depleting reservoirs” can refer to a pool of barcodes (e.g., stochastic barcodes) made up of many different labels. A non-depleting reservoir can comprise large numbers of different barcodes such that when the non-depleting reservoir is associated with a pool of targets each target is likely to be associated with a unique barcode. The uniqueness of each labeled target molecule can be determined by the statistics of random choice, and depends on the number of copies of identical target molecules in the collection compared to the diversity of labels. The size of the resulting set of labeled target molecules can be determined by the stochastic nature of the barcoding process, and analysis of the number of barcodes detected then allows calculation of the number of target molecules present in the original collection or sample. When the ratio of the number of copies of a target molecule present to the number of unique barcodes is low, the labeled target molecules are highly unique (i.e., there is a very low probability that more than one target molecule will have been labeled with a given label). 
     As used herein, the term “nucleic acid” refers to a polynucleotide sequence, or fragment thereof. A nucleic acid can comprise nucleotides. A nucleic acid can be exogenous or endogenous to a cell. A nucleic acid can exist in a cell-free environment. A nucleic acid can be a gene or fragment thereof. A nucleic acid can be DNA. A nucleic acid can be RNA. A nucleic acid can comprise one or more analogs (e.g., altered backbone, sugar, or nucleobase). Some non-limiting examples of analogs include: 5-bromouracil, peptide nucleic acid, xeno nucleic acid, morpholinos, locked nucleic acids, glycol nucleic acids, threose nucleic acids, dideoxynucleotides, cordycepin, 7-deaza-GTP, fluorophores (e.g., rhodamine or fluorescein linked to the sugar), thiol containing nucleotides, biotin linked nucleotides, fluorescent base analogs, CpG islands, methyl-7-guanosine, methylated nucleotides, inosine, thiouridine, pseudouridine, dihydrouridine, queuosine, and wyosine. “Nucleic acid”, “polynucleotide, “target polynucleotide”, and “target nucleic acid” can be used interchangeably. 
     A nucleic acid can comprise one or more modifications (e.g., a base modification, a backbone modification), to provide the nucleic acid with a new or enhanced feature (e.g., improved stability). A nucleic acid can comprise a nucleic acid affinity tag. A nucleoside can be a base-sugar combination. The base portion of the nucleoside can be a heterocyclic base. The two most common classes of such heterocyclic bases are the purines and the pyrimidines. Nucleotides can be nucleosides that further include a phosphate group covalently linked to the sugar portion of the nucleoside. For those nucleosides that include a pentofuranosyl sugar, the phosphate group can be linked to the 2′, the 3′, or the 5′ hydroxyl moiety of the sugar. In forming nucleic acids, the phosphate groups can covalently link adjacent nucleosides to one another to form a linear polymeric compound. In turn, the respective ends of this linear polymeric compound can be further joined to form a circular compound; however, linear compounds are generally suitable. In addition, linear compounds may have internal nucleotide base complementarity and may therefore fold in a manner as to produce a fully or partially double-stranded compound. Within nucleic acids, the phosphate groups can commonly be referred to as forming the internucleoside backbone of the nucleic acid. The linkage or backbone can be a 3′ to 5′ phosphodiester linkage. 
     A nucleic acid can comprise a modified backbone and/or modified internucleoside linkages. Modified backbones can include those that retain a phosphorus atom in the backbone and those that do not have a phosphorus atom in the backbone. Suitable modified nucleic acid backbones containing a phosphorus atom therein can include, for example, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkyl phosphotriesters, methyl and other alkyl phosphonate such as 3′-alkylene phosphonates, 5′-alkylene phosphonates, chiral phosphonates, phosphinates, phosphoramidates including 3′-amino phosphoramidate and aminoalkyl phosphoramidates, phosphorodiamidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, selenophosphates, and boranophosphates having normal 3′-5′ linkages, 2′-5′ linked analogs, and those having inverted polarity wherein one or more internucleotide linkages is a 3′ to 3′, a 5′ to 5′ or a 2′ to 2′ linkage. 
     A nucleic acid can comprise polynucleotide backbones that are formed by short chain alkyl or cycloalkyl internucleoside linkages, mixed heteroatom and alkyl or cycloalkyl internucleoside linkages, or one or more short chain heteroatomic or heterocyclic internucleoside linkages. These can include those having morpholino linkages (formed in part from the sugar portion of a nucleoside); siloxane backbones; sulfide, sulfoxide and sulfone backbones; formacetyl and thioformacetyl backbones; methylene formacetyl and thioformacetyl backbones; riboacetyl backbones; alkene containing backbones; sulfamate backbones; methyleneimino and methylenehydrazino backbones; sulfonate and sulfonamide backbones; amide backbones; and others having mixed N, O, S and CH 2  component parts. 
     A nucleic acid can comprise a nucleic acid mimetic. The term “mimetic” can be intended to include polynucleotides wherein only the furanose ring or both the furanose ring and the internucleotide linkage are replaced with non-furanose groups, replacement of only the furanose ring can also be referred as being a sugar surrogate. The heterocyclic base moiety or a modified heterocyclic base moiety can be maintained for hybridization with an appropriate target nucleic acid. One such nucleic acid can be a peptide nucleic acid (PNA). In a PNA, the sugar-backbone of a polynucleotide can be replaced with an amide containing backbone, in particular an aminoethylglycine backbone. The nucleotides can be retained and are bound directly or indirectly to aza nitrogen atoms of the amide portion of the backbone. The backbone in PNA compounds can comprise two or more linked aminoethylglycine units which gives PNA an amide containing backbone. The heterocyclic base moieties can be bound directly or indirectly to aza nitrogen atoms of the amide portion of the backbone. 
     A nucleic acid can comprise a morpholino backbone structure. For example, a nucleic acid can comprise a 6-membered morpholino ring in place of a ribose ring. In some of these embodiments, a phosphorodiamidate or other non-phosphodiester internucleoside linkage can replace a phosphodiester linkage. 
     A nucleic acid can comprise linked morpholino units (e.g., morpholino nucleic acid) having heterocyclic bases attached to the morpholino ring. Linking groups can link the morpholino monomeric units in a morpholino nucleic acid. Non-ionic morpholino-based oligomeric compounds can have less undesired interactions with cellular proteins. Morpholino-based polynucleotides can be nonionic mimics of nucleic acids. A variety of compounds within the morpholino class can be joined using different linking groups. A further class of polynucleotide mimetic can be referred to as cyclohexenyl nucleic acids (CeNA). The furanose ring normally present in a nucleic acid molecule can be replaced with a cyclohexenyl ring. CeNA DMT protected phosphoramidite monomers can be prepared and used for oligomeric compound synthesis using phosphoramidite chemistry. The incorporation of CeNA monomers into a nucleic acid chain can increase the stability of a DNA/RNA hybrid. CeNA oligoadenylates can form complexes with nucleic acid complements with similar stability to the native complexes. A further modification can include Locked Nucleic Acids (LNAs) in which the 2′-hydroxyl group is linked to the 4′ carbon atom of the sugar ring thereby forming a 2′-C, 4′-C-oxymethylene linkage thereby forming a bicyclic sugar moiety. The linkage can be a methylene (—CH 2 ), group bridging the 2′ oxygen atom and the 4′ carbon atom wherein n is 1 or 2. LNA and LNA analogs can display very high duplex thermal stabilities with complementary nucleic acid (Tm=+3 to +10° C.), stability towards 3′-exonucleolytic degradation and good solubility properties. 
     A nucleic acid may also include nucleobase (often referred to simply as “base”) modifications or substitutions. As used herein, “unmodified” or “natural” nucleobases can include the purine bases, (e.g., adenine (A) and guanine (G)), and the pyrimidine bases, (e.g., thymine (T), cytosine (C) and uracil (U)). Modified nucleobases can include other synthetic and natural nucleobases such as 5-methylcytosine (5-me-C), 5-hydroxymethyl cytosine, xanthine, hypoxanthine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine, 2-propyl and other alkyl derivatives of adenine and guanine, 2-thiouracil, 2-thiothymine and 2-thiocytosine, 5-halouracil and cytosine, 5-propynyl (—C═C—CH3) uracil and cytosine and other alkynyl derivatives of pyrimidine bases, 6-azo uracil, cytosine and thymine, 5-uracil (pseudouracil), 4-thiouracil, 8-halo, 8-amino, 8-thiol, 8-thioalkyl, 8-hydroxyl and other 8-substituted adenines and guanines, 5-halo particularly 5-bromo, 5-trifluoromethyl and other 5-substituted uracils and cytosines, 7-methylguanine and 7-methyladenine, 2-F-adenine, 2-aminoadenine, 8-azaguanine and 8-azaadenine, 7-deazaguanine and 7-deazaadenine and 3-deazaguanine and 3-deazaadenine. Modified nucleobases can include tricyclic pyrimidines such as phenoxazine cytidine (1H-pyrimido(5,4-b)(1,4)benzoxazin-2(3H)-one), phenothiazine cytidine (1H-pyrimido(5,4-b)(1,4)benzothiazin-2(3H)-one), G-clamps such as a substituted phenoxazine cytidine (e.g., 9-(2-aminoethoxy)-H-pyrimido(5,4-(b) (1,4)benzoxazin-2(3H)-one), phenothiazine cytidine (1H-pyrimido(5,4-b)(1,4)benzothiazin-2(3H)-one), G-clamps such as a substituted phenoxazine cytidine (e.g., 9-(2-aminoethoxy)-H-pyrimido(5,4-(b) (1,4)benzoxazin-2(3H)-one), carbazole cytidine (2H-pyrimido(4,5-b)indol-2-one), pyridoindole cytidine (H-pyrido(3′,2′:4,5)pyrrolo[2,3-d]pyrimidin-2-one). 
     As used herein, the term “sample” can refer to a composition comprising targets. Suitable samples for analysis by the disclosed methods, devices, and systems include cells, tissues, organs, or organisms. 
     As used herein, the term “sampling device” or “device” can refer to a device which may take a section of a sample and/or place the section on a substrate. A sample device can refer to, for example, a fluorescence activated cell sorting (FACS) machine, a cell sorter machine, a biopsy needle, a biopsy device, a tissue sectioning device, a microfluidic device, a blade grid, and/or a microtome. 
     As used herein, the term “solid support” can refer to discrete solid or semi-solid surfaces to which a plurality of barcodes (e.g., stochastic barcodes) may be attached. A solid support may encompass any type of solid, porous, or hollow sphere, ball, bearing, cylinder, or other similar configuration composed of plastic, ceramic, metal, or polymeric material (e.g., hydrogel) onto which a nucleic acid may be immobilized (e.g., covalently or non-covalently). A solid support may comprise a discrete particle that may be spherical (e.g., microspheres) or have a non-spherical or irregular shape, such as cubic, cuboid, pyramidal, cylindrical, conical, oblong, or disc-shaped, and the like. A bead can be non-spherical in shape. A plurality of solid supports spaced in an array may not comprise a substrate. A solid support may be used interchangeably with the term “bead.” 
     As used herein, the term “stochastic barcode” can refer to a polynucleotide sequence comprising labels of the present disclosure. A stochastic barcode can be a polynucleotide sequence that can be used for stochastic barcoding. Stochastic barcodes can be used to quantify targets within a sample. Stochastic barcodes can be used to control for errors which may occur after a label is associated with a target. For example, a stochastic barcode can be used to assess amplification or sequencing errors. A stochastic barcode associated with a target can be called a stochastic barcode-target or stochastic barcode-tag-target. 
     As used herein, the term “gene-specific stochastic barcode” can refer to a polynucleotide sequence comprising labels and a target-binding region that is gene-specific. A stochastic barcode can be a polynucleotide sequence that can be used for stochastic barcoding. Stochastic barcodes can be used to quantify targets within a sample. Stochastic barcodes can be used to control for errors which may occur after a label is associated with a target. For example, a stochastic barcode can be used to assess amplification or sequencing errors. A stochastic barcode associated with a target can be called a stochastic barcode-target or stochastic barcode-tag-target. 
     As used herein, the term “stochastic barcoding” can refer to the random labeling (e.g., barcoding) of nucleic acids. Stochastic barcoding can utilize a recursive Poisson strategy to associate and quantify labels associated with targets. As used herein, the term “stochastic barcoding” can be used interchangeably with “stochastic labeling.” 
     As used here, the term “target” can refer to a composition which can be associated with a barcode (e.g., a stochastic barcode). Exemplary suitable targets for analysis by the disclosed methods, devices, and systems include oligonucleotides, DNA, RNA, mRNA, microRNA, tRNA, and the like. Targets can be single or double stranded. In some embodiments, targets can be proteins, peptides, or polypeptides. In some embodiments, targets are lipids. As used herein, “target” can be used interchangeably with “species.” 
     As used herein, the term “reverse transcriptases” can refer to a group of enzymes having reverse transcriptase activity (i.e., that catalyze synthesis of DNA from an RNA template). In general, such enzymes include, but are not limited to, retroviral reverse transcriptase, retrotransposon reverse transcriptase, retroplasmid reverse transcriptases, retron reverse transcriptases, bacterial reverse transcriptases, group II intron-derived reverse transcriptase, and mutants, variants or derivatives thereof. Non-retroviral reverse transcriptases include non-LTR retrotransposon reverse transcriptases, retroplasmid reverse transcriptases, retron reverse transcriptases, and group II intron reverse transcriptases. Examples of group II intron reverse transcriptases include the  Lactococcus lactis  LI.LtrB intron reverse transcriptase, the  Thermosynechococcus elongatus  TeI4c intron reverse transcriptase, or the  Geobacillus stearothermophilus  GsI-IIC intron reverse transcriptase. Other classes of reverse transcriptases can include many classes of non-retroviral reverse transcriptases (i.e., retrons, group II introns, and diversity-generating retroelements among others). 
     The terms “universal adaptor primer,” “universal primer adaptor” or “universal adaptor sequence” are used interchangeably to refer to a nucleotide sequence that can be used to hybridize to barcodes (e.g., stochastic barcodes) to generate gene-specific barcodes. A universal adaptor sequence can, for example, be a known sequence that is universal across all barcodes used in methods of the disclosure. For example, when multiple targets are being labeled using the methods disclosed herein, each of the target-specific sequences may be linked to the same universal adaptor sequence. In some embodiments, more than one universal adaptor sequences may be used in the methods disclosed herein. For example, when multiple targets are being labeled using the methods disclosed herein, at least two of the target-specific sequences are linked to different universal adaptor sequences. A universal adaptor primer and its complement may be included in two oligonucleotides, one of which comprises a target-specific sequence and the other comprises a barcode. For example, a universal adaptor sequence may be part of an oligonucleotide comprising a target-specific sequence to generate a nucleotide sequence that is complementary to a target nucleic acid. A second oligonucleotide comprising a barcode and a complementary sequence of the universal adaptor sequence may hybridize with the nucleotide sequence and generate a target-specific barcode (e.g., a target-specific stochastic barcode). In some embodiments, a universal adaptor primer has a sequence that is different from a universal PCR primer used in the methods of this disclosure. 
     Barcodes 
     Barcoding, such as stochastic barcoding, has been described in, for example, Fu et al.,  Proc Natl Acad Sci U.S.A.,  2011 May 31, 108(22):9026-31; U.S. Patent Application Publication No. US2011/0160078; Fan et al.,  Science,  2015 Feb. 6, 347(6222):1258367; US Patent Application Publication No. US2015/0299784; and PCT Application Publication No. WO2015/031691; the content of each of these, including any supporting or supplemental information or material, is incorporated herein by reference in its entirety. In some embodiments, the barcode disclosed herein can be a stochastic barcode which can be a polynucleotide sequence that may be used to stochastically label (e.g., barcode, tag) a target. Barcodes can be referred to stochastic barcodes if the ratio of the number of different barcode sequences of the stochastic barcodes and the number of occurrence of any of the targets to be labeled can be, or be about, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, or a number or a range between any two of these values. A target can be an mRNA species comprising mRNA molecules with identical or nearly identical sequences. Barcodes can be referred to as stochastic barcodes if the ratio of the number of different barcode sequences of the stochastic barcodes and the number of occurrence of any of the targets to be labeled is at least, or is at most, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1. Barcode sequences of stochastic barcodes can be referred to as molecular labels. 
     A barcode, for example a stochastic barcode, can comprise one or more labels. Exemplary labels can include a universal label, a cell label, a barcode sequence (e.g., a molecular label), a sample label, a plate label, a spatial label, and/or a pre-spatial label.  FIG.  1    illustrates an exemplary barcode  104  with a spatial label. The barcode  104  can comprise a 5′ amine that may link the barcode to a solid support  108 . The barcode can comprise a universal label, a dimension label, a spatial label, a cell label, and/or a molecular label. The order of different labels (including but not limited to the universal label, the dimension label, the spatial label, the cell label, and the molecule label) in the barcode can vary. For example, as shown in  FIG.  1   , the universal label may be the 5′-most label, and the molecular label may be the 3′-most label. The spatial label, dimension label, and the cell label may be in any order. In some embodiments, the universal label, the spatial label, the dimension label, the cell label, and the molecular label are in any order. The barcode can comprise a target-binding region. The target-binding region can interact with a target (e.g., target nucleic acid, RNA, mRNA, DNA) in a sample. For example, a target-binding region can comprise an oligo(dT) sequence which can interact with poly(A) tails of mRNAs. In some instances, the labels of the barcode (e.g., universal label, dimension label, spatial label, cell label, and barcode sequence) may be separated by 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 or more nucleotides. 
     A label, for example the cell label, can comprise a unique set of nucleic acid sub-sequences of defined length, e.g., seven nucleotides each (equivalent to the number of bits used in some Hamming error correction codes), which can be designed to provide error correction capability. The set of error correction sub-sequences comprise seven nucleotide sequences can be designed such that any pairwise combination of sequences in the set exhibits a defined “genetic distance” (or number of mismatched bases), for example, a set of error correction sub-sequences can be designed to exhibit a genetic distance of three nucleotides. In this case, review of the error correction sequences in the set of sequence data for labeled target nucleic acid molecules (described more fully below) can allow one to detect or correct amplification or sequencing errors. In some embodiments, the length of the nucleic acid sub-sequences used for creating error correction codes can vary, for example, they can be, or be about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 31, 40, 50, or a number or a range between any two of these values, nucleotides in length. In some embodiments, nucleic acid sub-sequences of other lengths can be used for creating error correction codes. 
     The barcode can comprise a target-binding region. The target-binding region can interact with a target in a sample. The target can be, or comprise, ribonucleic acids (RNAs), messenger RNAs (mRNAs), microRNAs, small interfering RNAs (siRNAs), RNA degradation products, RNAs each comprising a poly(A) tail, or any combination thereof. In some embodiments, the plurality of targets can include deoxyribonucleic acids (DNAs). 
     In some embodiments, a target-binding region can comprise an oligo(dT) sequence which can interact with poly(A) tails of mRNAs. One or more of the labels of the barcode (e.g., the universal label, the dimension label, the spatial label, the cell label, and the barcode sequences (e.g., molecular label)) can be separated by a spacer from another one or two of the remaining labels of the barcode. The spacer can be, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20, or more nucleotides. In some embodiments, none of the labels of the barcode is separated by spacer. 
     Universal Labels 
     A barcode can comprise one or more universal labels. In some embodiments, the one or more universal labels can be the same for all barcodes in the set of barcodes attached to a given solid support. In some embodiments, the one or more universal labels can be the same for all barcodes attached to a plurality of beads. In some embodiments, a universal label can comprise a nucleic acid sequence that is capable of hybridizing to a sequencing primer. Sequencing primers can be used for sequencing barcodes comprising a universal label. Sequencing primers (e.g., universal sequencing primers) can comprise sequencing primers associated with high-throughput sequencing platforms. In some embodiments, a universal label can comprise a nucleic acid sequence that is capable of hybridizing to a PCR primer. In some embodiments, the universal label can comprise a nucleic acid sequence that is capable of hybridizing to a sequencing primer and a PCR primer. The nucleic acid sequence of the universal label that is capable of hybridizing to a sequencing or PCR primer can be referred to as a primer binding site. A universal label can comprise a sequence that can be used to initiate transcription of the barcode. A universal label can comprise a sequence that can be used for extension of the barcode or a region within the barcode. A universal label can be, or be about, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. For example, a universal label can comprise at least about 10 nucleotides. A universal label can be at least, or be at most, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, or 300 nucleotides in length. In some embodiments, a cleavable linker or modified nucleotide can be part of the universal label sequence to enable the barcode to be cleaved off from the support. 
     Dimension Labels 
     A barcode can comprise one or more dimension labels. In some embodiments, a dimension label can comprise a nucleic acid sequence that provides information about a dimension in which the labeling (e.g., stochastic labeling) occurred. For example, a dimension label can provide information about the time at which a target was barcoded. A dimension label can be associated with a time of barcoding (e.g., stochastic barcoding) in a sample. A dimension label can be activated at the time of labeling. Different dimension labels can be activated at different times. The dimension label provides information about the order in which targets, groups of targets, and/or samples were barcoded. For example, a population of cells can be barcoded at the G0 phase of the cell cycle. The cells can be pulsed again with barcodes (e.g., stochastic barcodes) at the G1 phase of the cell cycle. The cells can be pulsed again with barcodes at the S phase of the cell cycle, and so on. Barcodes at each pulse (e.g., each phase of the cell cycle), can comprise different dimension labels. In this way, the dimension label provides information about which targets were labelled at which phase of the cell cycle. Dimension labels can interrogate many different biological times. Exemplary biological times can include, but are not limited to, the cell cycle, transcription (e.g., transcription initiation), and transcript degradation. In another example, a sample (e.g., a cell, a population of cells) can be labeled before and/or after treatment with a drug and/or therapy. The changes in the number of copies of distinct targets can be indicative of the sample&#39;s response to the drug and/or therapy. 
     A dimension label can be activatable. An activatable dimension label can be activated at a specific time point. The activatable label can be, for example, constitutively activated (e.g., not turned off). The activatable dimension label can be, for example, reversibly activated (e.g., the activatable dimension label can be turned on and turned off). The dimension label can be, for example, reversibly activatable at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more times. The dimension label can be reversibly activatable, for example, at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more times. In some embodiments, the dimension label can be activated with fluorescence, light, a chemical event (e.g., cleavage, ligation of another molecule, addition of modifications (e.g., pegylated, sumoylated, acetylated, methylated, deacetylated, demethylated), a photochemical event (e.g., photocaging), and introduction of a non-natural nucleotide. 
     The dimension label can, in some embodiments, be identical for all barcodes (e.g., stochastic barcodes) attached to a given solid support (e.g., a bead), but different for different solid supports (e.g., beads). In some embodiments, at least 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99% or 100%, of barcodes on the same solid support can comprise the same dimension label. In some embodiments, at least 60% of barcodes on the same solid support can comprise the same dimension label. In some embodiments, at least 95% of barcodes on the same solid support can comprise the same dimension label. 
     There can be as many as 10 6  or more unique dimension label sequences represented in a plurality of solid supports (e.g., beads). A dimension label can be, or be about 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. A dimension label can be at least, or be at most, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, or 300, nucleotides in length. A dimension label can comprise between about 5 to about 200 nucleotides. A dimension label can comprise between about 10 to about 150 nucleotides. A dimension label can comprise between about 20 to about 125 nucleotides in length. 
     Spatial Labels 
     A barcode can comprise one or more spatial labels. In some embodiments, a spatial label can comprise a nucleic acid sequence that provides information about the spatial orientation of a target molecule which is associated with the barcode. A spatial label can be associated with a coordinate in a sample. The coordinate can be a fixed coordinate. For example, a coordinate can be fixed in reference to a substrate. A spatial label can be in reference to a two or three-dimensional grid. A coordinate can be fixed in reference to a landmark. The landmark can be identifiable in space. A landmark can be a structure which can be imaged. A landmark can be a biological structure, for example an anatomical landmark. A landmark can be a cellular landmark, for instance an organelle. A landmark can be a non-natural landmark such as a structure with an identifiable identifier such as a color code, bar code, magnetic property, fluorescents, radioactivity, or a unique size or shape. A spatial label can be associated with a physical partition (e.g., a well, a container, or a droplet). In some embodiments, multiple spatial labels are used together to encode one or more positions in space. 
     The spatial label can be identical for all barcodes attached to a given solid support (e.g., a bead), but different for different solid supports (e.g., beads). In some embodiments, the percentage of barcodes on the same solid support comprising the same spatial label can be, or be about, 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99%, 100%, or a number or a range between any two of these values. In some embodiments, the percentage of barcodes on the same solid support comprising the same spatial label can be at least, or be at most, 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99%, or 100%. In some embodiments, at least 60% of barcodes on the same solid support can comprise the same spatial label. In some embodiments, at least 95% of barcodes on the same solid support can comprise the same spatial label. 
     There can be as many as 10 6  or more unique spatial label sequences represented in a plurality of solid supports (e.g., beads). A spatial label can be, or be about, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. A spatial label can be at least or at most 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, or 300 nucleotides in length. A spatial label can comprise between about 5 to about 200 nucleotides. A spatial label can comprise between about 10 to about 150 nucleotides. A spatial label can comprise between about 20 to about 125 nucleotides in length. 
     Cell Labels 
     A barcode (e.g., a stochastic barcode) can comprise one or more cell labels. In some embodiments, a cell label can comprise a nucleic acid sequence that provides information for determining which target nucleic acid originated from which cell. In some embodiments, the cell label is identical for all barcodes attached to a given solid support (e.g., a bead), but different for different solid supports (e.g., beads). In some embodiments, the percentage of barcodes on the same solid support comprising the same cell label can be, or be about 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99%, 100%, or a number or a range between any two of these values. In some embodiments, the percentage of barcodes on the same solid support comprising the same cell label can be, or be about 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99%, or 100%. For example, at least 60% of barcodes on the same solid support can comprise the same cell label. As another example, at least 95% of barcodes on the same solid support can comprise the same cell label. 
     There can be as many as 10 6  or more unique cell label sequences represented in a plurality of solid supports (e.g., beads). A cell label can be, or be about, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. A cell label can be at least, or be at most, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, or 300 nucleotides in length. For example, a cell label can comprise between about 5 to about 200 nucleotides. As another example, a cell label can comprise between about 10 to about 150 nucleotides. As yet another example, a cell label can comprise between about 20 to about 125 nucleotides in length. 
     Barcode Sequences 
     A barcode can comprise one or more barcode sequences. In some embodiments, a barcode sequence can comprise a nucleic acid sequence that provides identifying information for the specific type of target nucleic acid species hybridized to the barcode. A barcode sequence can comprise a nucleic acid sequence that provides a counter (e.g., that provides a rough approximation) for the specific occurrence of the target nucleic acid species hybridized to the barcode (e.g., target-binding region). 
     In some embodiments, a diverse set of barcode sequences are attached to a given solid support (e.g., a bead). In some embodiments, there can be, or be about, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , or a number or a range between any two of these values, unique molecular label sequences. For example, a plurality of barcodes can comprise about 6561 barcodes sequences with distinct sequences. As another example, a plurality of barcodes can comprise about 65536 barcode sequences with distinct sequences. In some embodiments, there can be at least, or be at most, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , or 10 9 , unique barcode sequences. The unique molecular label sequences can be attached to a given solid support (e.g., a bead). 
     The length of a barcode can be different in different implementations. For example, a barcode can be, or be about, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. As another example, a barcode can be at least, or be at most, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, or 300 nucleotides in length. 
     Molecular Labels 
     A barcode (e.g., a stochastic barcode) can comprise one or more molecular labels. Molecular labels can include barcode sequences. In some embodiments, a molecular label can comprise a nucleic acid sequence that provides identifying information for the specific type of target nucleic acid species hybridized to the barcode. A molecular label can comprise a nucleic acid sequence that provides a counter for the specific occurrence of the target nucleic acid species hybridized to the barcode (e.g., target-binding region). 
     In some embodiments, a diverse set of molecular labels are attached to a given solid support (e.g., a bead). In some embodiments, there can be, or be about, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , or a number or a range between any two of these values, of unique molecular label sequences. For example, a plurality of barcodes can comprise about 6561 molecular labels with distinct sequences. As another example, a plurality of barcodes can comprise about 65536 molecular labels with distinct sequences. In some embodiments, there can be at least, or be at most, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , or 10 9 , unique molecular label sequences. Barcodes with unique molecular label sequences can be attached to a given solid support (e.g., a bead). 
     For stochastic barcoding using a plurality of stochastic barcodes, the ratio of the number of different molecular label sequences and the number of occurrence of any of the targets can be, or be about, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, or a number or a range between any two of these values. A target can be an mRNA species comprising mRNA molecules with identical or nearly identical sequences. In some embodiments, the ratio of the number of different molecular label sequences and the number of occurrence of any of the targets is at least, or is at most, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1. 
     A molecular label can be, or be about, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. A molecular label can be at least, or be at most, 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, 200, or 300 nucleotides in length. 
     Target-Binding Region 
     A barcode can comprise one or more target binding regions, such as capture probes. In some embodiments, a target-binding region can hybridize with a target of interest. In some embodiments, the target binding regions can comprise a nucleic acid sequence that hybridizes specifically to a target (e.g., target nucleic acid, target molecule, e.g., a cellular nucleic acid to be analyzed), for example to a specific gene sequence. In some embodiments, a target binding region can comprise a nucleic acid sequence that can attach (e.g., hybridize) to a specific location of a specific target nucleic acid. In some embodiments, the target binding region can comprise a nucleic acid sequence that is capable of specific hybridization to a restriction enzyme site overhang (e.g., an EcoRI sticky-end overhang). The barcode can then ligate to any nucleic acid molecule comprising a sequence complementary to the restriction site overhang. 
     In some embodiments, a target binding region can comprise a non-specific target nucleic acid sequence. A non-specific target nucleic acid sequence can refer to a sequence that can bind to multiple target nucleic acids, independent of the specific sequence of the target nucleic acid. For example, target binding region can comprise a random multimer sequence, or an oligo(dT) sequence that hybridizes to the poly(A) tail on mRNA molecules. A random multimer sequence can be, for example, a random dimer, trimer, quatramer, pentamer, hexamer, septamer, octamer, nonamer, decamer, or higher multimer sequence of any length. In some embodiments, the target binding region is the same for all barcodes attached to a given bead. In some embodiments, the target binding regions for the plurality of barcodes attached to a given bead can comprise two or more different target binding sequences. A target binding region can be, or be about, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, or a number or a range between any two of these values, nucleotides in length. A target binding region can be at most about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or more nucleotides in length. 
     In some embodiments, a target-binding region can comprise an oligo(dT) which can hybridize with mRNAs comprising polyadenylated ends. A target-binding region can be gene-specific. For example, a target-binding region can be configured to hybridize to a specific region of a target. A target-binding region can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 27, 28, 29, 30, or a number or a range between any two of these values, nucleotides in length. A target-binding region can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 27, 28, 29, or 30, nucleotides in length. A target-binding region can be about 5-30 nucleotides in length. When a barcode comprises a gene-specific target-binding region, the barcode can be referred to herein as a gene-specific barcode. 
     Orientation Property 
     A stochastic barcode (e.g., a stochastic barcode) can comprise one or more orientation properties which can be used to orient (e.g., align) the barcodes. A barcode can comprise a moiety for isoelectric focusing. Different barcodes can comprise different isoelectric focusing points. When these barcodes are introduced to a sample, the sample can undergo isoelectric focusing in order to orient the barcodes into a known way. In this way, the orientation property can be used to develop a known map of barcodes in a sample. Exemplary orientation properties can include, electrophoretic mobility (e.g., based on size of the barcode), isoelectric point, spin, conductivity, and/or self-assembly. For example, barcodes with an orientation property of self-assembly, can self-assemble into a specific orientation (e.g., nucleic acid nanostructure) upon activation. 
     Affinity Property 
     A barcode (e.g., a stochastic barcode) can comprise one or more affinity properties. For example, a spatial label can comprise an affinity property. An affinity property can include a chemical and/or biological moiety that can facilitate binding of the barcode to another entity (e.g., cell receptor). For example, an affinity property can comprise an antibody, for example, an antibody specific for a specific moiety (e.g., receptor) on a sample. In some embodiments, the antibody can guide the barcode to a specific cell type or molecule. Targets at and/or near the specific cell type or molecule can be labeled (e.g., stochastically labeled). The affinity property can, in some embodiments, provide spatial information in addition to the nucleotide sequence of the spatial label because the antibody can guide the barcode to a specific location. The antibody can be a therapeutic antibody, for example a monoclonal antibody or a polyclonal antibody. The antibody can be humanized or chimeric. The antibody can be a naked antibody or a fusion antibody. 
     The antibody can be a full-length (i.e., naturally occurring or formed by normal immunoglobulin gene fragment recombinatorial processes) immunoglobulin molecule (e.g., an IgG antibody) or an immunologically active (i.e., specifically binding) portion of an immunoglobulin molecule, like an antibody fragment. 
     The antibody fragment can be, for example, a portion of an antibody such as F(ab′)2, Fab′, Fab, Fv, sFv and the like. In some embodiments, the antibody fragment can bind with the same antigen that is recognized by the full-length antibody. The antibody fragment can include isolated fragments consisting of the variable regions of antibodies, such as the “Fv” fragments consisting of the variable regions of the heavy and light chains and recombinant single chain polypeptide molecules in which light and heavy variable regions are connected by a peptide linker (“scFv proteins”). Exemplary antibodies can include, but are not limited to, antibodies for cancer cells, antibodies for viruses, antibodies that bind to cell surface receptors (CD8, CD34, CD45), and therapeutic antibodies. 
     Universal Adaptor Primer 
     A barcode can comprise one or more universal adaptor primers. For example, a gene-specific barcode, such as a gene-specific stochastic barcode, can comprise a universal adaptor primer. A universal adaptor primer can refer to a nucleotide sequence that is universal across all barcodes. A universal adaptor primer can be used for building gene-specific barcodes. A universal adaptor primer can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 27, 28, 29, 30, or a number or a range between any two of these nucleotides in length. A universal adaptor primer can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26 27, 28, 29, or 30 nucleotides in length. A universal adaptor primer can be from 5-30 nucleotides in length. 
     Linker 
     When a barcode comprises more than one of a type of label (e.g., more than one cell label or more than one barcode sequence, such as one molecular label), the labels may be interspersed with a linker label sequence. A linker label sequence can be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or more nucleotides in length. A linker label sequence can be at most about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or more nucleotides in length. In some instances, a linker label sequence is 12 nucleotides in length. A linker label sequence can be used to facilitate the synthesis of the barcode. The linker label can comprise an error-correcting (e.g., Hamming) code. 
     Solid Supports 
     Barcodes, such as stochastic barcodes, disclosed herein can, in some embodiments, be associated with a solid support. The solid support can be, for example, a synthetic particle. In some embodiments, some or all of the barcode sequences, such as molecular labels for stochastic barcodes (e.g., the first barcode sequences) of a plurality of barcodes (e.g., the first plurality of barcodes) on a solid support differ by at least one nucleotide. The cell labels of the barcodes on the same solid support can be the same. The cell labels of the barcodes on different solid supports can differ by at least one nucleotide. For example, first cell labels of a first plurality of barcodes on a first solid support can have the same sequence, and second cell labels of a second plurality of barcodes on a second solid support can have the same sequence. The first cell labels of the first plurality of barcodes on the first solid support and the second cell labels of the second plurality of barcodes on the second solid support can differ by at least one nucleotide. A cell label can be, for example, about 5-20 nucleotides long. A barcode sequence can be, for example, about 5-20 nucleotides long. The synthetic particle can be, for example, a bead. 
     The bead can be, for example, a silica gel bead, a controlled pore glass bead, a magnetic bead, a Dynabead, a Sephadex/Sepharose bead, a cellulose bead, a polystyrene bead, or any combination thereof. The bead can comprise a material such as polydimethylsiloxane (PDMS), polystyrene, glass, polypropylene, agarose, gelatin, hydrogel, paramagnetic, ceramic, plastic, glass, methylstyrene, acrylic polymer, titanium, latex, Sepharose, cellulose, nylon, silicone, or any combination thereof. 
     In some embodiments, the bead can be a polymeric bead, for example a deformable bead or a gel bead, functionalized with barcodes or stochastic barcodes (such as gel beads from 10× Genomics (San Francisco, Calif.). In some implementation, a gel bead can comprise a polymer based gel. Gel beads can be generated, for example, by encapsulating one or more polymeric precursors into droplets. Upon exposure of the polymeric precursors to an accelerator (e.g., tetramethylethylenediamine (TEMED)), a gel bead may be generated. 
     In some embodiments, the particle can be degradable. For example, the polymeric bead can dissolve, melt, or degrade, for example, under a desired condition. The desired condition can include an environmental condition. The desired condition may result in the polymeric bead dissolving, melting, or degrading in a controlled manner. A gel bead may dissolve, melt, or degrade due to a chemical stimulus, a physical stimulus, a biological stimulus, a thermal stimulus, a magnetic stimulus, an electric stimulus, a light stimulus, or any combination thereof. 
     Analytes and/or reagents, such as oligonucleotide barcodes, for example, may be coupled/immobilized to the interior surface of a gel bead (e.g., the interior accessible via diffusion of an oligonucleotide barcode and/or materials used to generate an oligonucleotide barcode) and/or the outer surface of a gel bead or any other microcapsule described herein. Coupling/immobilization may be via any form of chemical bonding (e.g., covalent bond, ionic bond) or physical phenomena (e.g., Van der Waals forces, dipole-dipole interactions, etc.). In some embodiments, coupling/immobilization of a reagent to a gel bead or any other microcapsule described herein may be reversible, such as, for example, via a labile moiety (e.g., via a chemical cross-linker, including chemical cross-linkers described herein). Upon application of a stimulus, the labile moiety may be cleaved and the immobilized reagent set free. In some embodiments, the labile moiety is a disulfide bond. For example, in the case where an oligonucleotide barcode is immobilized to a gel bead via a disulfide bond, exposure of the disulfide bond to a reducing agent can cleave the disulfide bond and free the oligonucleotide barcode from the bead. The labile moiety may be included as part of a gel bead or microcapsule, as part of a chemical linker that links a reagent or analyte to a gel bead or microcapsule, and/or as part of a reagent or analyte. In some embodiments, at least one barcode of the plurality of barcodes can be immobilized on the particle, partially immobilized on the particle, enclosed in the particle, partially enclosed in the particle, or any combination thereof. 
     In some embodiments, a gel bead can comprise a wide range of different polymers including but not limited to: polymers, heat sensitive polymers, photosensitive polymers, magnetic polymers, pH sensitive polymers, salt-sensitive polymers, chemically sensitive polymers, polyelectrolytes, polysaccharides, peptides, proteins, and/or plastics. Polymers may include but are not limited to materials such as poly(N-isopropylacrylamide) (PNIPAAm), poly(styrene sulfonate) (PSS), poly(allyl amine) (PAAm), poly(acrylic acid) (PAA), poly(ethylene imine) (PEI), poly(diallyldimethyl-ammonium chloride) (PDADMAC), poly(pyrolle) (PPy), poly(vinylpyrrolidone) (PVPON), poly(vinyl pyridine) (PVP), poly(methacrylic acid) (PMAA), poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(tetrahydrofuran) (PTHF), poly(phthaladehyde) (PTHF), poly(hexyl viologen) (PHV), poly(L-lysine) (PLL), poly(L-arginine) (PARG), poly(lactic-co-glycolic acid) (PLGA). 
     Numerous chemical stimuli can be used to trigger the disruption, dissolution, or degradation of the beads. Examples of these chemical changes include, but are not limited to, pH-mediated changes to the bead wall, disintegration of the bead wall via chemical cleavage of crosslink bonds, triggered depolymerization of the bead wall, and bead wall switching reactions. Bulk changes may also be used to trigger disruption of the beads. 
     Bulk or physical changes to the microcapsule through various stimuli also offer many advantages in designing capsules to release reagents. Bulk or physical changes occur on a macroscopic scale, in which bead rupture is the result of mechano-physical forces induced by a stimulus. These processes may include, but are not limited to pressure induced rupture, bead wall melting, or changes in the porosity of the bead wall. 
     Biological stimuli may also be used to trigger disruption, dissolution, or degradation of beads. Generally, biological triggers resemble chemical triggers, but many examples use biomolecules, or molecules commonly found in living systems such as enzymes, peptides, saccharides, fatty acids, nucleic acids and the like. For example, beads may comprise polymers with peptide cross-links that are sensitive to cleavage by specific proteases. More specifically, one example may comprise a microcapsule comprising GFLGK peptide cross links. Upon addition of a biological trigger such as the protease Cathepsin B, the peptide cross links of the shell well are cleaved and the contents of the beads are released. In other cases, the proteases may be heat-activated. In another example, beads comprise a shell wall comprising cellulose. Addition of the hydrolytic enzyme chitosan serves as biologic trigger for cleavage of cellulosic bonds, depolymerization of the shell wall, and release of its inner contents. 
     The beads may also be induced to release their contents upon the application of a thermal stimulus. A change in temperature can cause a variety changes to the beads. A change in heat may cause melting of a bead such that the bead wall disintegrates. For example, the heat may increase the internal pressure of the inner components of the bead such that the bead ruptures or explodes. In some cases, the heat may transform the bead into a shrunken dehydrated state. The heat may also act upon heat-sensitive polymers within the wall of a bead to cause disruption of the bead. 
     Inclusion of magnetic nanoparticles to the bead wall of microcapsules may allow triggered rupture of the beads as well as guide the beads in an array. A device of this disclosure may comprise magnetic beads for either purpose. For example, incorporation of Fe 3 O 4  nanoparticles into polyelectrolyte containing beads triggers rupture in the presence of an oscillating magnetic field stimulus. 
     A bead may also be disrupted, dissolved, or degraded as the result of electrical stimulation. Similar to magnetic particles described in the previous section, electrically sensitive beads can allow for both triggered rupture of the beads as well as other functions such as alignment in an electric field, electrical conductivity or redox reactions. In one example, beads containing electrically sensitive material are aligned in an electric field such that release of inner reagents can be controlled. In other examples, electrical fields may induce redox reactions within the bead wall itself that may increase porosity. 
     A light stimulus may also be used to disrupt the beads. Numerous light triggers are possible and may include systems that use various molecules such as nanoparticles and chromophores capable of absorbing photons of specific ranges of wavelengths. For example, metal oxide coatings can be used as capsule triggers. UV irradiation of polyelectrolyte capsules coated with SiO 2  may result in disintegration of the bead wall. In yet another example, photo switchable materials such as azobenzene groups may be incorporated in the bead wall. Upon the application of UV or visible light, chemicals such as these undergo a reversible cis-to-trans isomerization upon absorption of photons. In this aspect, incorporation of photon switches result in a bead wall that may disintegrate or become more porous upon the application of a light trigger. 
     For example, in a non-limiting example of barcoding (e.g., stochastic barcoding) illustrated in  FIG.  2   , after introducing cells such as single cells onto a plurality of microwells of a microwell array at block  208 , beads can be introduced onto the plurality of microwells of the microwell array at block  212 . Each microwell can comprise one bead. The beads can comprise a plurality of barcodes. A barcode can comprise a 5′ amine region attached to a bead. The barcode can comprise a universal label, a barcode sequence (e.g., a molecular label), a target-binding region, or any combination thereof. 
     The barcodes disclosed herein can be associated with (e.g., attached to) a solid support (e.g., a bead). The barcodes associated with a solid support can each comprise a barcode sequence selected from a group comprising at least 100 or 1000 barcode sequences with unique sequences. In some embodiments, different barcodes associated with a solid support can comprise barcode with different sequences. In some embodiments, a percentage of barcodes associated with a solid support comprises the same cell label. For example, the percentage can be, or be about 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99%, 100%, or a number or a range between any two of these values. As another example, the percentage can be at least, or be at most 60%, 70%, 80%, 85%, 90%, 95%, 97%, 99%, or 100%. In some embodiments, barcodes associated with a solid support can have the same cell label. The barcodes associated with different solid supports can have different cell labels selected from a group comprising at least 100 or 1000 cell labels with unique sequences. 
     The barcodes disclosed herein can be associated to (e.g., attached to) a solid support (e.g., a bead). In some embodiments, barcoding the plurality of targets in the sample can be performed with a solid support including a plurality of synthetic particles associated with the plurality of barcodes. In some embodiments, the solid support can include a plurality of synthetic particles associated with the plurality of barcodes. The spatial labels of the plurality of barcodes on different solid supports can differ by at least one nucleotide. The solid support can, for example, include the plurality of barcodes in two dimensions or three dimensions. The synthetic particles can be beads. The beads can be silica gel beads, controlled pore glass beads, magnetic beads, Dynabeads, Sephadex/Sepharose beads, cellulose beads, polystyrene beads, or any combination thereof. The solid support can include a polymer, a matrix, a hydrogel, a needle array device, an antibody, or any combination thereof. In some embodiments, the solid supports can be free floating. In some embodiments, the solid supports can be embedded in a semi-solid or solid array. The barcodes may not be associated with solid supports. The barcodes can be individual nucleotides. The barcodes can be associated with a substrate. 
     As used herein, the terms “tethered,” “attached,” and “immobilized,” are used interchangeably, and can refer to covalent or non-covalent means for attaching barcodes to a solid support. Any of a variety of different solid supports can be used as solid supports for attaching pre-synthesized barcodes or for in situ solid-phase synthesis of barcode. 
     In some embodiments, the solid support is a bead. The bead can comprise one or more types of solid, porous, or hollow sphere, ball, bearing, cylinder, or other similar configuration which a nucleic acid can be immobilized (e.g., covalently or non-covalently). The bead can be, for example, composed of plastic, ceramic, metal, polymeric material, or any combination thereof. A bead can be, or comprise, a discrete particle that is spherical (e.g., microspheres) or have a non-spherical or irregular shape, such as cubic, cuboid, pyramidal, cylindrical, conical, oblong, or disc-shaped, and the like. In some embodiments, a bead can be non-spherical in shape. 
     Beads can comprise a variety of materials including, but not limited to, paramagnetic materials (e.g., magnesium, molybdenum, lithium, and tantalum), superparamagnetic materials (e.g., ferrite (Fe 3 O 4 ; magnetite) nanoparticles), ferromagnetic materials (e.g., iron, nickel, cobalt, some alloys thereof, and some rare earth metal compounds), ceramic, plastic, glass, polystyrene, silica, methylstyrene, acrylic polymers, titanium, latex, Sepharose, agarose, hydrogel, polymer, cellulose, nylon, or any combination thereof. 
     In some embodiments, the bead (e.g., the bead to which the labels are attached) is a hydrogel bead. In some embodiments, the bead comprises hydrogel. 
     Some embodiments disclosed herein include one or more particles (for example, beads). Each of the particles can comprise a plurality of oligonucleotides (e.g., barcodes). Each of the plurality of oligonucleotides can comprise a barcode sequence (e.g., a molecular label sequence), a cell label, and a target-binding region (e.g., an oligo(dT) sequence, a gene-specific sequence, a random multimer, or a combination thereof). The cell label sequence of each of the plurality of oligonucleotides can be the same. The cell label sequences of oligonucleotides on different particles can be different such that the oligonucleotides on different particles can be identified. The number of different cell label sequences can be different in different implementations. In some embodiments, the number of cell label sequences can be, or be about 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 10 6 , 10 7 , 10 8 , 10 9 , a number or a range between any two of these values, or more. In some embodiments, the number of cell label sequences can be at least, or be at most 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 10 6 , 10 7 , 10 8 , or 10 9 . In some embodiments, no more than 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or more of the plurality of the particles include oligonucleotides with the same cell sequence. In some embodiment, the plurality of particles that include oligonucleotides with the same cell sequence can be at most 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or more. In some embodiments, none of the plurality of the particles has the same cell label sequence. 
     The plurality of oligonucleotides on each particle can comprise different barcode sequences (e.g., molecular labels). In some embodiments, the number of barcode sequences can be, or be about 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 10 6 , 107, 10 8 , 109, or a number or a range between any two of these values. In some embodiments, the number of barcode sequences can be at least, or be at most 10, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000, 10 6 , 10 7 , 10 8 , or 10 9 . For example, at least 100 of the plurality of oligonucleotides comprise different barcode sequences. As another example, in a single particle, at least 100, 500, 1000, 5000, 10000, 15000, 20000, 50000, a number or a range between any two of these values, or more of the plurality of oligonucleotides comprise different barcode sequences. Some embodiments provide a plurality of the particles comprising barcodes. In some embodiments, the ratio of an occurrence (or a copy or a number) of a target to be labeled and the different barcode sequences can be at least 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or more. In some embodiments, each of the plurality of oligonucleotides further comprises a sample label, a universal label, or both. The particle can be, for example, a nanoparticle or microparticle. 
     The size of the beads can vary. For example, the diameter of the bead can range from 0.1 micrometer to 50 micrometers. In some embodiments, the diameter of the bead can be, or be about, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50 micrometers, or a number or a range between any two of these values. 
     The diameter of the bead can be related to the diameter of the wells of the substrate. In some embodiments, the diameter of the bead can be, or be about, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a number or a range between any two of these values, longer or shorter than the diameter of the well. The diameter of the beads can be related to the diameter of a cell (e.g., a single cell entrapped by a well of the substrate). In some embodiments, the diameter of the bead can be at least, or be at most, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% longer or shorter than the diameter of the well. The diameter of the beads can be related to the diameter of a cell (e.g., a single cell entrapped by a well of the substrate). In some embodiments, the diameter of the bead can be, or be about, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 150%, 200%, 250%, 300%, or a number or a range between any two of these values, longer or shorter than the diameter of the cell. In some embodiments, the diameter of the beads can be at least, or be at most, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 150%, 200%, 250%, or 300% longer or shorter than the diameter of the cell. 
     A bead can be attached to and/or embedded in a substrate. A bead can be attached to and/or embedded in a gel, hydrogel, polymer and/or matrix. The spatial position of a bead within a substrate (e.g., gel, matrix, scaffold, or polymer) can be identified using the spatial label present on the barcode on the bead which can serve as a location address. 
     Examples of beads can include, but are not limited to, streptavidin beads, agarose beads, magnetic beads, Dynabeads®, MACS® microbeads, antibody conjugated beads (e.g., anti-immunoglobulin microbeads), protein A conjugated beads, protein G conjugated beads, protein A/G conjugated beads, protein L conjugated beads, oligo(dT) conjugated beads, silica beads, silica-like beads, anti-biotin microbeads, anti-fluorochrome microbeads, and BcMag™ Carboxyl-Terminated Magnetic Beads. 
     A bead can be associated with (e.g., impregnated with) quantum dots or fluorescent dyes to make it fluorescent in one fluorescence optical channel or multiple optical channels. A bead can be associated with iron oxide or chromium oxide to make it paramagnetic or ferromagnetic. Beads can be identifiable. For example, a bead can be imaged using a camera. A bead can have a detectable code associated with the bead. For example, a bead can comprise a barcode. A bead can change size, for example, due to swelling in an organic or inorganic solution. A bead can be hydrophobic. A bead can be hydrophilic. A bead can be biocompatible. 
     A solid support (e.g., a bead) can be visualized. The solid support can comprise a visualizing tag (e.g., fluorescent dye). A solid support (e.g., a bead) can be etched with an identifier (e.g., a number). The identifier can be visualized through imaging the beads. 
     A solid support can comprise an insoluble, semi-soluble, or insoluble material. A solid support can be referred to as “functionalized” when it includes a linker, a scaffold, a building block, or other reactive moiety attached thereto, whereas a solid support may be “nonfunctionalized” when it lack such a reactive moiety attached thereto. The solid support can be employed free in solution, such as in a microtiter well format; in a flow-through format, such as in a column; or in a dipstick. 
     The solid support can comprise a membrane, paper, plastic, coated surface, flat surface, glass, slide, chip, or any combination thereof. A solid support can take the form of resins, gels, microspheres, or other geometric configurations. A solid support can comprise silica chips, microparticles, nanoparticles, plates, arrays, capillaries, flat supports such as glass fiber filters, glass surfaces, metal surfaces (steel, gold silver, aluminum, silicon and copper), glass supports, plastic supports, silicon supports, chips, filters, membranes, microwell plates, slides, plastic materials including multiwell plates or membranes (e.g., formed of polyethylene, polypropylene, polyamide, polyvinylidenedifluoride), and/or wafers, combs, pins or needles (e.g., arrays of pins suitable for combinatorial synthesis or analysis) or beads in an array of pits or nanoliter wells of flat surfaces such as wafers (e.g., silicon wafers), wafers with pits with or without filter bottoms. 
     The solid support can comprise a polymer matrix (e.g., gel, hydrogel). The polymer matrix may be able to permeate intracellular space (e.g., around organelles). The polymer matrix may able to be pumped throughout the circulatory system. 
     Substrates and Microwell Array 
     As used herein, a substrate can refer to a type of solid support. A substrate can refer to a solid support that can comprise barcodes or stochastic barcodes of the disclosure. A substrate can, for example, comprise a plurality of microwells. For example, a substrate can be a well array comprising two or more microwells. In some embodiments, a microwell can comprise a small reaction chamber of defined volume. In some embodiments, a microwell can entrap one or more cells. In some embodiments, a microwell can entrap only one cell. In some embodiments, a microwell can entrap one or more solid supports. In some embodiments, a microwell can entrap only one solid support. In some embodiments, a microwell entraps a single cell and a single solid support (e.g., a bead). A microwell can comprise barcode reagents of the disclosure. 
     Methods of Barcoding 
     The disclosure provides for methods for estimating the number of distinct targets at distinct locations in a physical sample (e.g., tissue, organ, tumor, cell). The methods can comprise placing barcodes (e.g., stochastic barcodes) in close proximity with the sample, lysing the sample, associating distinct targets with the barcodes, amplifying the targets and/or digitally counting the targets. The method can further comprise analyzing and/or visualizing the information obtained from the spatial labels on the barcodes. In some embodiments, a method comprises visualizing the plurality of targets in the sample. Mapping the plurality of targets onto the map of the sample can include generating a two dimensional map or a three dimensional map of the sample. The two dimensional map and the three dimensional map can be generated prior to or after barcoding (e.g., stochastically barcoding) the plurality of targets in the sample. Visualizing the plurality of targets in the sample can include mapping the plurality of targets onto a map of the sample. Mapping the plurality of targets onto the map of the sample can include generating a two dimensional map or a three dimensional map of the sample. The two dimensional map and the three dimensional map can be generated prior to or after barcoding the plurality of targets in the sample. in some embodiments, the two dimensional map and the three dimensional map can be generated before or after lysing the sample. Lysing the sample before or after generating the two dimensional map or the three dimensional map can include heating the sample, contacting the sample with a detergent, changing the pH of the sample, or any combination thereof. 
     In some embodiments, barcoding the plurality of targets comprises hybridizing a plurality of barcodes with a plurality of targets to create barcoded targets (e.g., stochastically barcoded targets). Barcoding the plurality of targets can comprise generating an indexed library of the barcoded targets. Generating an indexed library of the barcoded targets can be performed with a solid support comprising the plurality of barcodes (e.g., stochastic barcodes). 
     Contacting a Sample and a Barcode 
     The disclosure provides for methods for contacting a sample (e.g., cells) to a substrate of the disclosure. A sample comprising, for example, a cell, organ, or tissue thin section, can be contacted to barcodes (e.g., stochastic barcodes). The cells can be contacted, for example, by gravity flow wherein the cells can settle and create a monolayer. The sample can be a tissue thin section. The thin section can be placed on the substrate. The sample can be one-dimensional (e.g., forms a planar surface). The sample (e.g., cells) can be spread across the substrate, for example, by growing/culturing the cells on the substrate. 
     When barcodes are in close proximity to targets, the targets can hybridize to the barcode. The barcodes can be contacted at a non-depletable ratio such that each distinct target can associate with a distinct barcode of the disclosure. To ensure efficient association between the target and the barcode, the targets can be cross-linked to barcode. 
     Cell Lysis 
     Following the distribution of cells and barcodes, the cells can be lysed to liberate the target molecules. Cell lysis can be accomplished by any of a variety of means, for example, by chemical or biochemical means, by osmotic shock, or by means of thermal lysis, mechanical lysis, or optical lysis. Cells can be lysed by addition of a cell lysis buffer comprising a detergent (e.g., SDS, Li dodecyl sulfate, Triton X-100, Tween-20, or NP-40), an organic solvent (e.g., methanol or acetone), or digestive enzymes (e.g., proteinase K, pepsin, or trypsin), or any combination thereof. To increase the association of a target and a barcode, the rate of the diffusion of the target molecules can be altered by for example, reducing the temperature and/or increasing the viscosity of the lysate. 
     In some embodiments, the sample can be lysed using a filter paper. The filter paper can be soaked with a lysis buffer on top of the filter paper. The filter paper can be applied to the sample with pressure which can facilitate lysis of the sample and hybridization of the targets of the sample to the substrate. 
     In some embodiments, lysis can be performed by mechanical lysis, heat lysis, optical lysis, and/or chemical lysis. Chemical lysis can include the use of digestive enzymes such as proteinase K, pepsin, and trypsin. Lysis can be performed by the addition of a lysis buffer to the substrate. A lysis buffer can comprise Tris HCl. A lysis buffer can comprise at least about 0.01, 0.05, 0.1, 0.5, or 1 M or more Tris HCl. A lysis buffer can comprise at most about 0.01, 0.05, 0.1, 0.5, or 1 M or more Tris HCL. A lysis buffer can comprise about 0.1 M Tris HCl. The pH of the lysis buffer can be at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more. The pH of the lysis buffer can be at most about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more. In some embodiments, the pH of the lysis buffer is about 7.5. The lysis buffer can comprise a salt (e.g., LiCl). The concentration of salt in the lysis buffer can be at least about 0.1, 0.5, or 1 M or more. The concentration of salt in the lysis buffer can be at most about 0.1, 0.5, or 1 M or more. In some embodiments, the concentration of salt in the lysis buffer is about 0.5M. The lysis buffer can comprise a detergent (e.g., SDS, Li dodecyl sulfate, triton X, tween, NP-40). The concentration of the detergent in the lysis buffer can be at least about 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3% 4%, 5%, 6%, or 7%, or more. The concentration of the detergent in the lysis buffer can be at most about 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, or 7%, or more. In some embodiments, the concentration of the detergent in the lysis buffer is about 1% Li dodecyl sulfate. The time used in the method for lysis can be dependent on the amount of detergent used. In some embodiments, the more detergent used, the less time needed for lysis. The lysis buffer can comprise a chelating agent (e.g., EDTA, EGTA). The concentration of a chelating agent in the lysis buffer can be at least about 1, 5, 10, 15, 20, 25, or 30 mM or more. The concentration of a chelating agent in the lysis buffer can be at most about 1, 5, 10, 15, 20, 25, or 30 mM or more. In some embodiments, the concentration of chelating agent in the lysis buffer is about 10 mM. The lysis buffer can comprise a reducing reagent (e.g., beta-mercaptoethanol, DTT). The concentration of the reducing reagent in the lysis buffer can be at least about 1, 5, 10, 15, or 20 mM or more. The concentration of the reducing reagent in the lysis buffer can be at most about 1, 5, 10, 15, or 20 mM or more. In some embodiments, the concentration of reducing reagent in the lysis buffer is about 5 mM. In some embodiments, a lysis buffer can comprise about 0.1M TrisHCl, about pH 7.5, about 0.5M LiCl, about 1% lithium dodecyl sulfate, about 10 mM EDTA, and about 5 mM DTT. 
     Lysis can be performed at a temperature of about 4, 10, 15, 20, 25, or 30° C. Lysis can be performed for about 1, 5, 10, 15, or 20 or more minutes. A lysed cell can comprise at least about 100000, 200000, 300000, 400000, 500000, 600000, or 700000 or more target nucleic acid molecules. A lysed cell can comprise at most about 100000, 200000, 300000, 400000, 500000, 600000, or 700000 or more target nucleic acid molecules. 
     Attachment of Barcodes to Target Nucleic Acid Molecules 
     Following lysis of the cells and release of nucleic acid molecules therefrom, the nucleic acid molecules can randomly associate with the barcodes of the co-localized solid support. Association can comprise hybridization of a barcode&#39;s target recognition region to a complementary portion of the target nucleic acid molecule (e.g., oligo(dT) of the barcode can interact with a poly(A) tail of a target). The assay conditions used for hybridization (e.g., buffer pH, ionic strength, temperature, etc.) can be chosen to promote formation of specific, stable hybrids. In some embodiments, the nucleic acid molecules released from the lysed cells can associate with the plurality of probes on the substrate (e.g., hybridize with the probes on the substrate). When the probes comprise oligo(dT), mRNA molecules can hybridize to the probes and be reverse transcribed. The oligo(dT) portion of the oligonucleotide can act as a primer for first strand synthesis of the cDNA molecule. For example, in a non-limiting example of barcoding illustrated in  FIG.  2   , at block  216 , mRNA molecules can hybridize to barcodes on beads. For example, single-stranded nucleotide fragments can hybridize to the target-binding regions of barcodes. 
     Attachment can further comprise ligation of a barcode&#39;s target recognition region and a portion of the target nucleic acid molecule. For example, the target binding region can comprise a nucleic acid sequence that can be capable of specific hybridization to a restriction site overhang (e.g., an EcoRI sticky-end overhang). The assay procedure can further comprise treating the target nucleic acids with a restriction enzyme (e.g., EcoRI) to create a restriction site overhang. The barcode can then be ligated to any nucleic acid molecule comprising a sequence complementary to the restriction site overhang. A ligase (e.g., T4 DNA ligase) can be used to join the two fragments. 
     For example, in a non-limiting example of barcoding illustrated in  FIG.  2   , at block  220 , the labeled targets from a plurality of cells (or a plurality of samples) (e.g., target-barcode molecules) can be subsequently pooled, for example, into a tube. The labeled targets can be pooled by, for example, retrieving the barcodes and/or the beads to which the target-barcode molecules are attached. 
     The retrieval of solid support-based collections of attached target-barcode molecules can be implemented by use of magnetic beads and an externally-applied magnetic field. Once the target-barcode molecules have been pooled, all further processing can proceed in a single reaction vessel. Further processing can include, for example, reverse transcription reactions, amplification reactions, cleavage reactions, dissociation reactions, and/or nucleic acid extension reactions. Further processing reactions can be performed within the microwells, that is, without first pooling the labeled target nucleic acid molecules from a plurality of cells. 
     Reverse Transcription 
     The disclosure provides for a method to create a target-barcode conjugate using reverse transcription (e.g., at block  224  of  FIG.  2   ). The target-barcode conjugate can comprise the barcode and a complementary sequence of all or a portion of the target nucleic acid (i.e., a barcoded cDNA molecule, such as a stochastically barcoded cDNA molecule). Reverse transcription of the associated RNA molecule can occur by the addition of a reverse transcription primer along with the reverse transcriptase. The reverse transcription primer can be an oligo(dT) primer, a random hexanucleotide primer, or a target-specific oligonucleotide primer. Oligo(dT) primers can be, or can be about, 12-18 nucleotides in length and bind to the endogenous poly(A) tail at the 3′ end of mammalian mRNA. Random hexanucleotide primers can bind to mRNA at a variety of complementary sites. Target-specific oligonucleotide primers typically selectively prime the mRNA of interest. 
     In some embodiments, reverse transcription of the labeled-RNA molecule can occur by the addition of a reverse transcription primer. In some embodiments, the reverse transcription primer is an oligo(dT) primer, random hexanucleotide primer, or a target-specific oligonucleotide primer. Generally, oligo(dT) primers are 12-18 nucleotides in length and bind to the endogenous poly(A) tail at the 3′ end of mammalian mRNA. Random hexanucleotide primers can bind to mRNA at a variety of complementary sites. Target-specific oligonucleotide primers typically selectively prime the mRNA of interest. 
     Reverse transcription can occur repeatedly to produce multiple labeled-cDNA molecules. The methods disclosed herein can comprise conducting at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 reverse transcription reactions. The method can comprise conducting at least about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 reverse transcription reactions. 
     Amplification 
     One or more nucleic acid amplification reactions (e.g., at block  228  of  FIG.  2   ) can be performed to create multiple copies of the labeled target nucleic acid molecules. Amplification can be performed in a multiplexed manner, wherein multiple target nucleic acid sequences are amplified simultaneously. The amplification reaction can be used to add sequencing adaptors to the nucleic acid molecules. The amplification reactions can comprise amplifying at least a portion of a sample label, if present. The amplification reactions can comprise amplifying at least a portion of the cellular label and/or barcode sequence (e.g., a molecular label). The amplification reactions can comprise amplifying at least a portion of a sample tag, a cell label, a spatial label, a barcode sequence (e.g., a molecular label), a target nucleic acid, or a combination thereof. The amplification reactions can comprise amplifying 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 100%, or a range or a number between any two of these values, of the plurality of nucleic acids. The method can further comprise conducting one or more cDNA synthesis reactions to produce one or more cDNA copies of target-barcode molecules comprising a sample label, a cell label, a spatial label, and/or a barcode sequence (e.g., a molecular label). 
     In some embodiments, amplification can be performed using a polymerase chain reaction (PCR). As used herein, PCR can refer to a reaction for the in vitro amplification of specific DNA sequences by the simultaneous primer extension of complementary strands of DNA. As used herein, PCR can encompass derivative forms of the reaction, including but not limited to, RT-PCR, real-time PCR, nested PCR, quantitative PCR, multiplexed PCR, digital PCR, and assembly PCR. 
     Amplification of the labeled nucleic acids can comprise non-PCR based methods. Examples of non-PCR based methods include, but are not limited to, multiple displacement amplification (MDA), transcription-mediated amplification (TMA), nucleic acid sequence-based amplification (NASBA), strand displacement amplification (SDA), real-time SDA, rolling circle amplification, or circle-to-circle amplification. Other non-PCR-based amplification methods include multiple cycles of DNA-dependent RNA polymerase-driven RNA transcription amplification or RNA-directed DNA synthesis and transcription to amplify DNA or RNA targets, a ligase chain reaction (LCR), and a Q replicase (QP) method, use of palindromic probes, strand displacement amplification, oligonucleotide-driven amplification using a restriction endonuclease, an amplification method in which a primer is hybridized to a nucleic acid sequence and the resulting duplex is cleaved prior to the extension reaction and amplification, strand displacement amplification using a nucleic acid polymerase lacking 5′ exonuclease activity, rolling circle amplification, and ramification extension amplification (RAM). In some embodiments, the amplification does not produce circularized transcripts. 
     In some embodiments, the methods disclosed herein further comprise conducting a polymerase chain reaction on the labeled nucleic acid (e.g., labeled-RNA, labeled-DNA, labeled-cDNA) to produce a labeled amplicon (e.g., a stochastically labeled amplicon). The labeled amplicon can be double-stranded molecule. The double-stranded molecule can comprise a double-stranded RNA molecule, a double-stranded DNA molecule, or a RNA molecule hybridized to a DNA molecule. One or both of the strands of the double-stranded molecule can comprise a sample label, a spatial label, a cell label, and/or a barcode sequence (e.g., a molecular label). The labeled amplicon can be a single-stranded molecule. The single-stranded molecule can comprise DNA, RNA, or a combination thereof. The nucleic acids of the disclosure can comprise synthetic or altered nucleic acids. 
     Amplification can comprise use of one or more non-natural nucleotides. Non-natural nucleotides can comprise photolabile or triggerable nucleotides. Examples of non-natural nucleotides can include, but are not limited to, peptide nucleic acid (PNA), morpholino and locked nucleic acid (LNA), as well as glycol nucleic acid (GNA) and threose nucleic acid (TNA). Non-natural nucleotides can be added to one or more cycles of an amplification reaction. The addition of the non-natural nucleotides can be used to identify products as specific cycles or time points in the amplification reaction. 
     Conducting the one or more amplification reactions can comprise the use of one or more primers. The one or more primers can comprise, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 or more nucleotides. The one or more primers can comprise at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 or more nucleotides. The one or more primers can comprise less than 12-15 nucleotides. The one or more primers can anneal to at least a portion of the plurality of labeled targets (e.g., stochastically labeled targets). The one or more primers can anneal to the 3′ end or 5′ end of the plurality of labeled targets. The one or more primers can anneal to an internal region of the plurality of labeled targets. The internal region can be at least about 50, 100, 150, 200, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 650, 700, 750, 800, 850, 900 or 1000 nucleotides from the 3′ ends the plurality of labeled targets. The one or more primers can comprise a fixed panel of primers. The one or more primers can comprise at least one or more custom primers. The one or more primers can comprise at least one or more control primers. The one or more primers can comprise at least one or more gene-specific primers. 
     The one or more primers can comprise a universal primer. The universal primer can anneal to a universal primer binding site. The one or more custom primers can anneal to a first sample label, a second sample label, a spatial label, a cell label, a barcode sequence (e.g., a molecular label), a target, or any combination thereof. The one or more primers can comprise a universal primer and a custom primer. The custom primer can be designed to amplify one or more targets. The targets can comprise a subset of the total nucleic acids in one or more samples. The targets can comprise a subset of the total labeled targets in one or more samples. The one or more primers can comprise at least 96 or more custom primers. The one or more primers can comprise at least 960 or more custom primers. The one or more primers can comprise at least 9600 or more custom primers. The one or more custom primers can anneal to two or more different labeled nucleic acids. The two or more different labeled nucleic acids can correspond to one or more genes. 
     Any amplification scheme can be used in the methods of the present disclosure. For example, in one scheme, the first round PCR can amplify molecules attached to the bead using a gene specific primer and a primer against the universal Illumina sequencing primer 1 sequence. The second round of PCR can amplify the first PCR products using a nested gene specific primer flanked by Illumina sequencing primer 2 sequence, and a primer against the universal Illumina sequencing primer 1 sequence. The third round of PCR adds P5 and P7 and sample index to turn PCR products into an Illumina sequencing library. Sequencing using 150 bp×2 sequencing can reveal the cell label and barcode sequence (e.g., molecular label) on read 1, the gene on read 2, and the sample index on index 1 read. 
     In some embodiments, nucleic acids can be removed from the substrate using chemical cleavage. For example, a chemical group or a modified base present in a nucleic acid can be used to facilitate its removal from a solid support. For example, an enzyme can be used to remove a nucleic acid from a substrate. For example, a nucleic acid can be removed from a substrate through a restriction endonuclease digestion. For example, treatment of a nucleic acid containing a dUTP or ddUTP with uracil-d-glycosylase (UDG) can be used to remove a nucleic acid from a substrate. For example, a nucleic acid can be removed from a substrate using an enzyme that performs nucleotide excision, such as a base excision repair enzyme, such as an apurinic/apyrimidinic (AP) endonuclease. In some embodiments, a nucleic acid can be removed from a substrate using a photocleavable group and light. In some embodiments, a cleavable linker can be used to remove a nucleic acid from the substrate. For example, the cleavable linker can comprise at least one of biotin/avidin, biotin/streptavidin, biotin/neutravidin, Ig-protein A, a photolabile linker, acid or base labile linker group, or an aptamer. 
     When the probes are gene-specific, the molecules can hybridize to the probes and be reverse transcribed and/or amplified. In some embodiments, after the nucleic acid has been synthesized (e.g., reverse transcribed), it can be amplified. Amplification can be performed in a multiplex manner, wherein multiple target nucleic acid sequences are amplified simultaneously. Amplification can add sequencing adaptors to the nucleic acid. 
     In some embodiments, amplification can be performed on the substrate, for example, with bridge amplification. cDNAs can be homopolymer tailed in order to generate a compatible end for bridge amplification using oligo(dT) probes on the substrate. In bridge amplification, the primer that is complementary to the 3′ end of the template nucleic acid can be the first primer of each pair that is covalently attached to the solid particle. When a sample containing the template nucleic acid is contacted with the particle and a single thermal cycle is performed, the template molecule can be annealed to the first primer and the first primer is elongated in the forward direction by addition of nucleotides to form a duplex molecule consisting of the template molecule and a newly formed DNA strand that is complementary to the template. In the heating step of the next cycle, the duplex molecule can be denatured, releasing the template molecule from the particle and leaving the complementary DNA strand attached to the particle through the first primer. In the annealing stage of the annealing and elongation step that follows, the complementary strand can hybridize to the second primer, which is complementary to a segment of the complementary strand at a location removed from the first primer. This hybridization can cause the complementary strand to form a bridge between the first and second primers secured to the first primer by a covalent bond and to the second primer by hybridization. In the elongation stage, the second primer can be elongated in the reverse direction by the addition of nucleotides in the same reaction mixture, thereby converting the bridge to a double-stranded bridge. The next cycle then begins, and the double-stranded bridge can be denatured to yield two single-stranded nucleic acid molecules, each having one end attached to the particle surface via the first and second primers, respectively, with the other end of each unattached. In the annealing and elongation step of this second cycle, each strand can hybridize to a further complementary primer, previously unused, on the same particle, to form new single-strand bridges. The two previously unused primers that are now hybridized elongate to convert the two new bridges to double-strand bridges. 
     The amplification reactions can comprise amplifying at least 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, or 100% of the plurality of nucleic acids. 
     Amplification of the labeled nucleic acids can comprise PCR-based methods or non-PCR based methods. Amplification of the labeled nucleic acids can comprise exponential amplification of the labeled nucleic acids. Amplification of the labeled nucleic acids can comprise linear amplification of the labeled nucleic acids. Amplification can be performed by polymerase chain reaction (PCR). PCR can refer to a reaction for the in vitro amplification of specific DNA sequences by the simultaneous primer extension of complementary strands of DNA. PCR can encompass derivative forms of the reaction, including but not limited to, RT-PCR, real-time PCR, nested PCR, quantitative PCR, multiplexed PCR, digital PCR, suppression PCR, semi-suppressive PCR and assembly PCR. 
     In some embodiments, amplification of the labeled nucleic acids comprises non-PCR based methods. Examples of non-PCR based methods include, but are not limited to, multiple displacement amplification (MDA), transcription-mediated amplification (TMA), nucleic acid sequence-based amplification (NASBA), strand displacement amplification (SDA), real-time SDA, rolling circle amplification, or circle-to-circle amplification. Other non-PCR-based amplification methods include multiple cycles of DNA-dependent RNA polymerase-driven RNA transcription amplification or RNA-directed DNA synthesis and transcription to amplify DNA or RNA targets, a ligase chain reaction (LCR), a Q replicase (QP), use of palindromic probes, strand displacement amplification, oligonucleotide-driven amplification using a restriction endonuclease, an amplification method in which a primer is hybridized to a nucleic acid sequence and the resulting duplex is cleaved prior to the extension reaction and amplification, strand displacement amplification using a nucleic acid polymerase lacking 5′ exonuclease activity, rolling circle amplification, and/or ramification extension amplification (RAM). 
     In some embodiments, the methods disclosed herein further comprise conducting a nested polymerase chain reaction on the amplified amplicon (e.g., target). The amplicon can be double-stranded molecule. The double-stranded molecule can comprise a double-stranded RNA molecule, a double-stranded DNA molecule, or a RNA molecule hybridized to a DNA molecule. One or both of the strands of the double-stranded molecule can comprise a sample tag or molecular identifier label. Alternatively, the amplicon can be a single-stranded molecule. The single-stranded molecule can comprise DNA, RNA, or a combination thereof. The nucleic acids of the present invention can comprise synthetic or altered nucleic acids. 
     In some embodiments, the method comprises repeatedly amplifying the labeled nucleic acid to produce multiple amplicons. The methods disclosed herein can comprise conducting at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 amplification reactions. Alternatively, the method comprises conducting at least about 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 amplification reactions. 
     Amplification can further comprise adding one or more control nucleic acids to one or more samples comprising a plurality of nucleic acids. Amplification can further comprise adding one or more control nucleic acids to a plurality of nucleic acids. The control nucleic acids can comprise a control label. 
     Amplification can comprise use of one or more non-natural nucleotides. Non-natural nucleotides can comprise photolabile and/or triggerable nucleotides. Examples of non-natural nucleotides include, but are not limited to, peptide nucleic acid (PNA), morpholino and locked nucleic acid (LNA), as well as glycol nucleic acid (GNA) and threose nucleic acid (TNA). Non-natural nucleotides can be added to one or more cycles of an amplification reaction. The addition of the non-natural nucleotides can be used to identify products as specific cycles or time points in the amplification reaction. 
     Conducting the one or more amplification reactions can comprise the use of one or more primers. The one or more primers can comprise one or more oligonucleotides. The one or more oligonucleotides can comprise at least about 7-9 nucleotides. The one or more oligonucleotides can comprise less than 12-15 nucleotides. The one or more primers can anneal to at least a portion of the plurality of labeled nucleic acids. The one or more primers can anneal to the 3′ end and/or 5′ end of the plurality of labeled nucleic acids. The one or more primers can anneal to an internal region of the plurality of labeled nucleic acids. The internal region can be at least about 50, 100, 150, 200, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 650, 700, 750, 800, 850, 900 or 1000 nucleotides from the 3′ ends the plurality of labeled nucleic acids. The one or more primers can comprise a fixed panel of primers. The one or more primers can comprise at least one or more custom primers. The one or more primers can comprise at least one or more control primers. The one or more primers can comprise at least one or more housekeeping gene primers. The one or more primers can comprise a universal primer. The universal primer can anneal to a universal primer binding site. The one or more custom primers can anneal to the first sample tag, the second sample tag, the molecular identifier label, the nucleic acid or a product thereof. The one or more primers can comprise a universal primer and a custom primer. The custom primer can be designed to amplify one or more target nucleic acids. The target nucleic acids can comprise a subset of the total nucleic acids in one or more samples. In some embodiments, the primers are the probes attached to the array of the disclosure. 
     In some embodiments, barcoding (e.g., stochastically barcoding) the plurality of targets in the sample further comprises generating an indexed library of the barcoded targets (e.g., stochastically barcoded targets) or barcoded fragments of the targets. The barcode sequences of different barcodes (e.g., the molecular labels of different stochastic barcodes) can be different from one another. Generating an indexed library of the barcoded targets includes generating a plurality of indexed polynucleotides from the plurality of targets in the sample. For example, for an indexed library of the barcoded targets comprising a first indexed target and a second indexed target, the label region of the first indexed polynucleotide can differ from the label region of the second indexed polynucleotide by, by about, by at least, or by at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, or a number or a range between any two of these values, nucleotides. In some embodiments, generating an indexed library of the barcoded targets includes contacting a plurality of targets, for example mRNA molecules, with a plurality of oligonucleotides including a poly(T) region and a label region; and conducting a first strand synthesis using a reverse transcriptase to produce single-strand labeled cDNA molecules each comprising a cDNA region and a label region, wherein the plurality of targets includes at least two mRNA molecules of different sequences and the plurality of oligonucleotides includes at least two oligonucleotides of different sequences. Generating an indexed library of the barcoded targets can further comprise amplifying the single-strand labeled cDNA molecules to produce double-strand labeled cDNA molecules; and conducting nested PCR on the double-strand labeled cDNA molecules to produce labeled amplicons. In some embodiments, the method can include generating an adaptor-labeled amplicon. 
     Barcoding (e.g., stochastic barcoding) can include using nucleic acid barcodes or tags to label individual nucleic acid (e.g., DNA or RNA) molecules. In some embodiments, it involves adding DNA barcodes or tags to cDNA molecules as they are generated from mRNA. Nested PCR can be performed to minimize PCR amplification bias. Adaptors can be added for sequencing using, for example, next generation sequencing (NGS). The sequencing results can be used to determine cell labels, molecular labels, and sequences of nucleotide fragments of the one or more copies of the targets, for example at block  232  of  FIG.  2   . 
       FIG.  3    is a schematic illustration showing a non-limiting exemplary process of generating an indexed library of the barcoded targets (e.g., stochastically barcoded targets), such as barcoded mRNAs or fragments thereof. As shown in step 1, the reverse transcription process can encode each mRNA molecule with a unique molecular label, a cell label, and a universal PCR site. In particular, RNA molecules  302  can be reverse transcribed to produce labeled cDNA molecules  304 , including a cDNA region  306 , by hybridization (e.g., stochastic hybridization) of a set of barcodes (e.g., stochastic barcodes)  310  to the poly(A) tail region  308  of the RNA molecules  302 . Each of the barcodes  310  can comprise a target-binding region, for example a poly(dT) region  312 , a label region  314  (e.g., a barcode sequence or a molecule), and a universal PCR region  316 . 
     In some embodiments, the cell label can include 3 to 20 nucleotides. In some embodiments, the molecular label can include 3 to 20 nucleotides. In some embodiments, each of the plurality of stochastic barcodes further comprises one or more of a universal label and a cell label, wherein universal labels are the same for the plurality of stochastic barcodes on the solid support and cell labels are the same for the plurality of stochastic barcodes on the solid support. In some embodiments, the universal label can include 3 to 20 nucleotides. In some embodiments, the cell label comprises 3 to 20 nucleotides. 
     In some embodiments, the label region  314  can include a barcode sequence or a molecular label  318  and a cell label  320 . In some embodiments, the label region  314  can include one or more of a universal label, a dimension label, and a cell label. The barcode sequence or molecular label  318  can be, can be about, can be at least, or can be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any of these values, of nucleotides in length. The cell label  320  can be, can be about, can be at least, or can be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any of these values, of nucleotides in length. The universal label can be, can be about, can be at least, or can be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any of these values, of nucleotides in length. Universal labels can be the same for the plurality of stochastic barcodes on the solid support and cell labels are the same for the plurality of stochastic barcodes on the solid support. The dimension label can be, can be about, can be at least, or can be at most 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any of these values, of nucleotides in length. 
     In some embodiments, the label region  314  can comprise, comprise about, comprise at least, or comprise at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or a number or a range between any of these values, different labels, such as a barcode sequence or a molecular label  318  and a cell label  320 . Each label can be, can be about, can be at least, or can be at most 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any of these values, of nucleotides in length. A set of barcodes or stochastic barcodes  310  can contain, contain about, contain at least, or can be at most, 10, 20, 40, 50, 70, 80, 90, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , 10 10 , 10 11 , 10 12 , 10 13 , 10 14 , 10 15 , 10 20 , or a number or a range between any of these values, barcodes or stochastic barcodes  310 . And the set of barcodes or stochastic barcodes  310  can, for example, each contain a unique label region  314 . The labeled cDNA molecules  304  can be purified to remove excess barcodes or stochastic barcodes  310 . Purification can comprise Ampure bead purification. 
     As shown in step 2, products from the reverse transcription process in step 1 can be pooled into 1 tube and PCR amplified with a 1 st  PCR primer pool and a 1 st  universal PCR primer. Pooling is possible because of the unique label region  314 . In particular, the labeled cDNA molecules  304  can be amplified to produce nested PCR labeled amplicons  322 . Amplification can comprise multiplex PCR amplification. Amplification can comprise a multiplex PCR amplification with 96 multiplex primers in a single reaction volume. In some embodiments, multiplex PCR amplification can utilize, utilize about, utilize at least, or utilize at most, 10, 20, 40, 50, 70, 80, 90, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 , 10 10 , 10 11 , 10 12 , 10 13 , 10 14 , 10 15 , 10 20 , or a number or a range between any of these values, multiplex primers in a single reaction volume. Amplification can comprise using a 1 st  PCR primer pool  324  comprising custom primers  326 A-C targeting specific genes and a universal primer  328 . The custom primers  326  can hybridize to a region within the cDNA portion  306 ′ of the labeled cDNA molecule  304 . The universal primer  328  can hybridize to the universal PCR region  316  of the labeled cDNA molecule  304 . 
     As shown in step 3 of  FIG.  3   , products from PCR amplification in step 2 can be amplified with a nested PCR primers pool and a 2 nd  universal PCR primer. Nested PCR can minimize PCR amplification bias. In particular, the nested PCR labeled amplicons  322  can be further amplified by nested PCR. The nested PCR can comprise multiplex PCR with nested PCR primers pool  330  of nested PCR primers  332   a - c  and a 2 nd  universal PCR primer  328 ′ in a single reaction volume. The nested PCR primer pool  328  can contain, contain about, contain at least, or contain at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or a number or a range between any of these values, different nested PCR primers  330 . The nested PCR primers  332  can contain an adaptor  334  and hybridize to a region within the cDNA portion  306 ″ of the labeled amplicon  322 . The universal primer  328 ′ can contain an adaptor  336  and hybridize to the universal PCR region  316  of the labeled amplicon  322 . Thus, step 3 produces adaptor-labeled amplicon  338 . In some embodiments, nested PCR primers  332  and the 2 nd  universal PCR primer  328 ′ may not contain the adaptors  334  and  336 . The adaptors  334  and  336  can instead be ligated to the products of nested PCR to produce adaptor-labeled amplicon  338 . 
     As shown in step 4, PCR products from step 3 can be PCR amplified for sequencing using library amplification primers. In particular, the adaptors  334  and  336  can be used to conduct one or more additional assays on the adaptor-labeled amplicon  338 . The adaptors  334  and  336  can be hybridized to primers  340  and  342 . The one or more primers  340  and  342  can be PCR amplification primers. The one or more primers  340  and  342  can be sequencing primers. The one or more adaptors  334  and  336  can be used for further amplification of the adaptor-labeled amplicons  338 . The one or more adaptors  334  and  336  can be used for sequencing the adaptor-labeled amplicon  338 . The primer  342  can contain a plate index  344  so that amplicons generated using the same set of barcodes or stochastic barcodes  310  can be sequenced in one sequencing reaction using next generation sequencing (NGS). 
     Compositions Comprising Cellular Component Binding Reagents Associated with Oligonucleotides 
     Some embodiments disclosed herein provide a plurality of compositions each comprising a cellular component binding reagent (such as a protein binding reagent) that is conjugated with an oligonucleotide, wherein the oligonucleotide comprises a unique identifier for the cellular component binding reagent that it is conjugated with. Cellular component binding reagents (such as barcoded antibodies) and their uses (such as sample indexing of cells) have been described in U U.S. Patent Application Publication No. US2018/0088112 and U.S. Patent Application Publication No. US2018/0346970; the content of each of these is incorporated herein by reference in its entirety. 
     In some embodiments, the cellular component binding reagent is capable of specifically binding to a cellular component target. For example, a binding target of the cellular component binding reagent can be, or comprise, a carbohydrate, a lipid, a protein, an extracellular protein, a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, a major histocompatibility complex, a tumor antigen, a receptor, an integrin, an intracellular protein, or any combination thereof. In some embodiments, the cellular component binding reagent (e.g., a protein binding reagent) is capable of specifically binding to an antigen target or a protein target. In some embodiments, each of the oligonucleotides can comprise a barcode, such as a stochastic barcode. A barcode can comprise a barcode sequence (e.g., a molecular label), a cell label, a sample label, or any combination thereof. In some embodiments, each of the oligonucleotides can comprise a linker. In some embodiments, each of the oligonucleotides can comprise a binding site for an oligonucleotide probe, such as a poly(A) tail. For example, the poly(A) tail can be, e.g., unanchored to a solid support or anchored to a solid support. The poly(A) tail can be from about 10 to 50 nucleotides in length. In some embodiments, the poly(A) tail can be 18 nucleotides in length. The oligonucleotides can comprise deoxyribonucleotides, ribonucleotides, or both. 
     The unique identifiers can be, for example, a nucleotide sequence having any suitable length, for example, from about 4 nucleotides to about 200 nucleotides. In some embodiments, the unique identifier is a nucleotide sequence of 25 nucleotides to about 45 nucleotides in length. In some embodiments, the unique identifier can have a length that is, is about, is less than, is greater than, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, 10 nucleotides, 15 nucleotides, 20 nucleotides, 25 nucleotides, 30 nucleotides, 35 nucleotides, 40 nucleotides, 45 nucleotides, 50 nucleotides, 55 nucleotides, 60 nucleotides, 70 nucleotides, 80 nucleotides, 90 nucleotides, 100 nucleotides, 200 nucleotides, or a range that is between any two of the above values. 
     In some embodiments, the unique identifiers are selected from a diverse set of unique identifiers. The diverse set of unique identifiers can comprise, or comprise about, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 5000, or a number or a range between any two of these values, different unique identifiers. The diverse set of unique identifiers can comprise at least, or comprise at most, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, or 5000, different unique identifiers. In some embodiments, the set of unique identifiers is designed to have minimal sequence homology to the DNA or RNA sequences of the sample to be analyzed. In some embodiments, the sequences of the set of unique identifiers are different from each other, or the complement thereof, by, or by about, 1 nucleotide, 2 nucleotides, 3 nucleotides, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, 10 nucleotides, or a number or a range between any two of these values. In some embodiments, the sequences of the set of unique identifiers are different from each other, or the complement thereof, by at least, or by at most, 1 nucleotide, 2 nucleotides, 3 nucleotides, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, 10 nucleotides. In some embodiments, the sequences of the set of unique identifiers are different from each other, or the complement thereof, by at least 3%, at least 5%, at least 8%, at least 10%, at least 15%, at least 20%, or more. 
     In some embodiments, the unique identifiers can comprise a binding site for a primer, such as universal primer. In some embodiments, the unique identifiers can comprise at least two binding sites for a primer, such as a universal primer. In some embodiments, the unique identifiers can comprise at least three binding sites for a primer, such as a universal primer. The primers can be used for amplification of the unique identifiers, for example, by PCR amplification. In some embodiments, the primers can be used for nested PCR reactions. 
     Any suitable cellular component binding reagents are contemplated in this disclosure, such as protein binding reagents, antibodies or fragments thereof, aptamers, small molecules, ligands, peptides, oligonucleotides, etc., or any combination thereof. In some embodiments, the cellular component binding reagents can be polyclonal antibodies, monoclonal antibodies, recombinant antibodies, single chain antibody (sc-Ab), or fragments thereof, such as Fab, Fv, etc. In some embodiments, the plurality of cellular component binding reagents can comprise, or comprise about, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 5000, or a number or a range between any two of these values, different cellular component reagents. In some embodiments, the plurality of cellular component binding reagents can comprise at least, or comprise at most, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, or 5000, different cellular component reagents. 
     The oligonucleotide can be conjugated with the cellular component binding reagent through various mechanism. In some embodiments, the oligonucleotide can be conjugated with the cellular component binding reagent covalently. In some embodiment, the oligonucleotide can be conjugated with the cellular component binding reagent non-covalently. In some embodiments, the oligonucleotide is conjugated with the cellular component binding reagent through a linker. The linker can be, for example, cleavable or detachable from the cellular component binding reagent and/or the oligonucleotide. In some embodiments, the linker can comprise a chemical group that reversibly attaches the oligonucleotide to the cellular component binding reagents. The chemical group can be conjugated to the linker, for example, through an amine group. In some embodiments, the linker can comprise a chemical group that forms a stable bond with another chemical group conjugated to the cellular component binding reagent. For example, the chemical group can be a UV photocleavable group, a disulfide bond, a streptavidin, a biotin, an amine, etc. In some embodiments, the chemical group can be conjugated to the cellular component binding reagent through a primary amine on an amino acid, such as lysine, or the N-terminus. Commercially available conjugation kits, such as the Protein-Oligo Conjugation Kit (Solulink, Inc., San Diego, Calif.), the Thunder-Link® oligo conjugation system (Innova Biosciences, Cambridge, United Kingdom), etc., can be used to conjugate the oligonucleotide to the cellular component binding reagent. 
     The oligonucleotide can be conjugated to any suitable site of the cellular component binding reagent (e.g., a protein binding reagent), as long as it does not interfere with the specific binding between the cellular component binding reagent and its cellular component target. In some embodiments, the cellular component binding reagent is a protein, such as an antibody. In some embodiments, the cellular component binding reagent is not an antibody. In some embodiments, the oligonucleotide can be conjugated to the antibody anywhere other than the antigen-binding site, for example, the Fc region, the C H 1 domain, the C H 2 domain, the C H 3 domain, the C L  domain, etc. Methods of conjugating oligonucleotides to cellular component binding reagents (e.g., antibodies) have been previously disclosed, for example, in U.S. Pat. No. 6,531,283, the content of which is hereby expressly incorporated by reference in its entirety. Stoichiometry of oligonucleotide to cellular component binding reagent can be varied. To increase the sensitivity of detecting the cellular component binding reagent specific oligonucleotide in sequencing, it may be advantageous to increase the ratio of oligonucleotide to cellular component binding reagent during conjugation. In some embodiments, each cellular component binding reagent can be conjugated with a single oligonucleotide molecule. In some embodiments, each cellular component binding reagent can be conjugated with more than one oligonucleotide molecule, for example, at least, or at most, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, or a number or a range between any two of these values, oligonucleotide molecules wherein each of the oligonucleotide molecule comprises the same, or different, unique identifiers. In some embodiments, each cellular component binding reagent can be conjugated with more than one oligonucleotide molecule, for example, at least, or at most, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, oligonucleotide molecules, wherein each of the oligonucleotide molecule comprises the same, or different, unique identifiers. 
     In some embodiments, the plurality of cellular component binding reagents is capable of specifically binding to a plurality of cellular component targets in a sample, such as a single cell, a plurality of cells, a tissue sample, a tumor sample, a blood sample, or the like. In some embodiments, the plurality of cellular component targets comprises a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, an antibody, a major histocompatibility complex, a tumor antigen, a receptor, or any combination thereof. In some embodiments, the plurality of cellular component targets can comprise intracellular cellular components. In some embodiments, the plurality of cellular component targets can comprise intracellular cellular components. In some embodiments, the plurality of cellular components can be, or be about, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99%, or a number or a range between any two of these values, of all the cellular components (e.g., proteins) in a cell or an organism. In some embodiments, the plurality of cellular components can be at least, or be at most, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, or 99%, of all the cellular components (e.g., proteins) in a cell or an organism. In some embodiments, the plurality of cellular component targets can comprise, or comprise about, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, 10000, or a number or a range between any two of these values, different cellular component targets. In some embodiments, the plurality of cellular component targets can comprise at least, or comprise at most, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, 10000, different cellular component targets. 
       FIG.  4    shows a schematic illustration of an exemplary cellular component binding reagent (e.g., an antibody) that is associated (e.g., conjugated) with an oligonucleotide comprising a unique identifier sequence for the antibody. An oligonucleotide-conjugated with a cellular component binding reagent, an oligonucleotide for conjugation with a cellular component binding reagent, or an oligonucleotide previously conjugated with a cellular component binding reagent can be referred to herein as an antibody oligonucleotide (abbreviated as a binding reagent oligonucleotide). An oligonucleotide-conjugated with an antibody, an oligonucleotide for conjugation with an antibody, or an oligonucleotide previously conjugated with an antibody can be referred to herein as an antibody oligonucleotide (abbreviated as an “AbOligo” or “AbO”). The oligonucleotide can also comprise additional components, including but not limited to, one or more linker, one or more unique identifier for the antibody, optionally one or more barcode sequences (e.g., molecular labels), and a poly(A) tail. In some embodiments, the oligonucleotide can comprise, from 5′ to 3′, a linker, a unique identifier, a barcode sequence (e.g., a molecular label), and a poly(A) tail. An antibody oligonucleotide can be an mRNA mimic. 
       FIG.  5    shows a schematic illustration of an exemplary cellular component binding reagent (e.g., an antibody) that is associated (e.g., conjugated) with an oligonucleotide comprising a unique identifier sequence for the antibody. The cellular component binding reagent can be capable of specifically binding to at least one cellular component target, such as an antigen target or a protein target. A binding reagent oligonucleotide (e.g., a sample indexing oligonucleotide, or an antibody oligonucleotide) can comprise a sequence (e.g., a sample indexing sequence) for performing the methods of the disclosure. For example, a sample indexing oligonucleotide can comprise a sample indexing sequence for identifying sample origin of one or more cells of a sample. Indexing sequences (e.g., sample indexing sequences) of at least two compositions comprising two cellular component binding reagents (e.g., sample indexing compositions) of the plurality of compositions comprising cellular component binding reagents can comprise different sequences. In some embodiments, the binding reagent oligonucleotide is not homologous to genomic sequences of a species. The binding reagent oligonucleotide can be configured to be (or can be) detachable or non-detachable from the cellular component binding reagent. 
     The oligonucleotide conjugated to a cellular component binding reagent can, for example, comprise a barcode sequence (e.g., a molecular label sequence), a poly(A) tail, or a combination thereof. An oligonucleotide conjugated to a cellular component binding reagent can be an mRNA mimic. In some embodiments, the sample indexing oligonucleotide comprises a sequence complementary to a capture sequence of at least one barcode of the plurality of barcodes. A target binding region of the barcode can comprise the capture sequence. The target binding region can, for example, comprise a poly(dT) region. In some embodiments, the sequence of the sample indexing oligonucleotide complementary to the capture sequence of the barcode can comprise a poly(A) tail. The sample indexing oligonucleotide can comprise a molecular label. 
     In some embodiments, the binding reagent oligonucleotide (e.g., the sample oligonucleotide) comprises a nucleotide sequence of, or a nucleotide sequence of about, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 128, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, or a number or a range between any two of these values, nucleotides in length. In some embodiments, the binding reagent oligonucleotide comprises a nucleotide sequence of at least, or of at most, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 128, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, or 1000, nucleotides in length. 
     In some embodiments, the cellular component binding reagent comprises an antibody, a tetramer, an aptamer, a protein scaffold, or a combination thereof. The binding reagent oligonucleotide can be conjugated to the cellular component binding reagent, for example, through a linker. The binding reagent oligonucleotide can comprise the linker. The linker can comprise a chemical group. The chemical group can be reversibly, or irreversibly, attached to the molecule of the cellular component binding reagent. The chemical group can be selected from the group consisting of a UV photocleavable group, a disulfide bond, a streptavidin, a biotin, an amine, and any combination thereof. 
     In some embodiments, the cellular component binding reagent can bind to ADAM10, CD156c, ANO6, ATP1B2, ATP1B3, BSG, CD147, CD109, CD230, CD29, CD298, ATP1B3, CD44, CD45, CD47, CD51, CD59, CD63, CD97, CD98, SLC3A2, CLDND1, HLA-ABC, ICAM1, ITFG3, MPZL1, NA K ATPase alpha1, ATP1A1, NPTN, PMCA ATPase, ATP2B1, SLC1A5, SLC29A1, SLC2A1, SLC44A2, or any combination thereof. 
     In some embodiments, the protein target is, or comprises, an extracellular protein, an intracellular protein, or any combination thereof. In some embodiments, the antigen or protein target is, or comprises, a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, a major histocompatibility complex, a tumor antigen, a receptor, an integrin, or any combination thereof. The antigen or protein target can be, or comprise, a lipid, a carbohydrate, or any combination thereof. The protein target can be selected from a group comprising a number of protein targets. The number of antigen target or protein targets can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, or a number or a range between any two of these values. The number of protein targets can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or 10000. 
     The cellular component binding reagent (e.g., a protein binding reagent) can be associated with two or more binding reagent oligonucleotide (e.g., sample indexing oligonucleotides) with an identical sequence. The cellular component binding reagent can be associated with two or more binding reagent oligonucleotides with different sequences. The number of binding reagent oligonucleotides associated with the cellular component binding reagent can be different in different implementations. In some embodiments, the number of binding reagent oligonucleotides, whether having an identical sequence, or different sequences, can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, or a number or a range between any two of these values. In some embodiments, the number of binding reagent oligonucleotides can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000. 
     The plurality of compositions comprising cellular component binding reagents (e.g., the plurality of sample indexing compositions) can comprise one or more additional cellular component binding reagents not conjugated with the binding reagent oligonucleotide (such as sample indexing oligonucleotide), which is also referred to herein as the binding reagent oligonucleotide-free cellular component binding reagent (such as sample indexing oligonucleotide-free cellular component binding reagent). The number of additional cellular component binding reagents in the plurality of compositions can be different in different implementations. In some embodiments, the number of additional cellular component binding reagents can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any two of these values. In some embodiments, the number of additional cellular component binding reagents can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. The cellular component binding reagent and any of the additional cellular component binding reagents can be identical, in some embodiments. 
     In some embodiments, a mixture comprising cellular component binding reagent(s) that is conjugated with one or more binding reagent oligonucleotides (e.g., sample indexing oligonucleotides) and cellular component binding reagent(s) that is not conjugated with binding reagent oligonucleotides is provided. The mixture can be used in some embodiments of the methods disclosed herein, for example, to contact the sample(s) and/or cell(s). The ratio of (1) the number of a cellular component binding reagent conjugated with a binding reagent oligonucleotide and (2) the number of another cellular component binding reagent (e.g., the same cellular component binding reagent) not conjugated with the binding reagent oligonucleotide (e.g., sample indexing oligonucleotide) or other binding reagent oligonucleotide(s) in the mixture can be different in different implementations. In some embodiments, the ratio can be, or be about, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.5, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29, 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39, 1:40, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:48, 1:49, 1:50, 1:51, 1:52, 1:53, 1:54, 1:55, 1:56, 1:57, 1:58, 1:59, 1:60, 1:61, 1:62, 1:63, 1:64, 1:65, 1:66, 1:67, 1:68, 1:69, 1:70, 1:71, 1:72, 1:73, 1:74, 1:75, 1:76, 1:77, 1:78, 1:79, 1:80, 1:81, 1:82, 1:83, 1:84, 1:85, 1:86, 1:87, 1:88, 1:89, 1:90, 1:91, 1:92, 1:93, 1:94, 1:95, 1:96, 1:97, 1:98, 1:99, 1:100, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800, 1:900, 1:1000, 1:2000, 1:3000, 1:4000, 1:5000, 1:6000, 1:7000, 1:8000, 1:9000, 1:10000, or a number or a range between any two of the values. In some embodiments, the ratio can be at least, or be at most, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.5, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, 1:21, 1:22, 1:23, 1:24, 1:25, 1:26, 1:27, 1:28, 1:29, 1:30, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39, 1:40, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:48, 1:49, 1:50, 1:51, 1:52, 1:53, 1:54, 1:55, 1:56, 1:57, 1:58, 1:59, 1:60, 1:61, 1:62, 1:63, 1:64, 1:65, 1:66, 1:67, 1:68, 1:69, 1:70, 1:71, 1:72, 1:73, 1:74, 1:75, 1:76, 1:77, 1:78, 1:79, 1:80, 1:81, 1:82, 1:83, 1:84, 1:85, 1:86, 1:87, 1:88, 1:89, 1:90, 1:91, 1:92, 1:93, 1:94, 1:95, 1:96, 1:97, 1:98, 1:99, 1:100, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800, 1:900, 1:1000, 1:2000, 1:3000, 1:4000, 1:5000, 1:6000, 1:7000, 1:8000, 1:9000, or 1:10000. 
     In some embodiments, the ratio can be, or be about, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, 35:1, 36:1, 37:1, 38:1, 39:1, 40:1, 41:1, 42:1, 43:1, 44:1, 45:1, 46:1, 47:1, 48:1, 49:1, 50:1, 51:1, 52:1, 53:1, 54:1, 55:1, 56:1, 57:1, 58:1, 59:1, 60:1, 61:1, 62:1, 63:1, 64:1, 65:1, 66:1, 67:1, 68:1, 69:1, 70:1, 71:1, 72:1, 73:1, 74:1, 75:1, 76:1, 77:1, 78:1, 79:1, 80:1, 81:1, 82:1, 83:1, 84:1, 85:1, 86:1, 87:1, 88:1, 89:1, 90:1, 91:1, 92:1, 93:1, 94:1, 95:1, 96:1, 97:1, 98:1, 99:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 2000:1, 3000:1, 4000:1, 5000:1, 6000:1, 7000:1, 8000:1, 9000:1, 10000:1, or a number or a range between any two of the values. In some embodiments, the ratio can be at least, or be at most, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.5:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, 35:1, 36:1, 37:1, 38:1, 39:1, 40:1, 41:1, 42:1, 43:1, 44:1, 45:1, 46:1, 47:1, 48:1, 49:1, 50:1, 51:1, 52:1, 53:1, 54:1, 55:1, 56:1, 57:1, 58:1, 59:1, 60:1, 61:1, 62:1, 63:1, 64:1, 65:1, 66:1, 67:1, 68:1, 69:1, 70:1, 71:1, 72:1, 73:1, 74:1, 75:1, 76:1, 77:1, 78:1, 79:1, 80:1, 81:1, 82:1, 83:1, 84:1, 85:1, 86:1, 87:1, 88:1, 89:1, 90:1, 91:1, 92:1, 93:1, 94:1, 95:1, 96:1, 97:1, 98:1, 99:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 2000:1, 3000:1, 4000:1, 5000:1, 6000:1, 7000:1, 8000:1, 9000:1, or 10000:1. 
     A cellular component binding reagent can be conjugated with a binding reagent oligonucleotide (e.g., a sample indexing oligonucleotide), or not. In some embodiments, the percentage of the cellular component binding reagent conjugated with a binding reagent oligonucleotide (e.g., a sample indexing oligonucleotide) in a mixture comprising the cellular component binding reagent that is conjugated with the binding reagent oligonucleotide and the cellular component binding reagent(s) that is not conjugated with the binding reagent oligonucleotide can be, or be about, 0.000000001%, 0.00000001%, 0.0000001%, 0.000001%, 0.00001%, 0.0001%, 0.001%, 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a number or a range between any two of these values. In some embodiments, the percentage of the cellular component binding reagent conjugated with a sample indexing oligonucleotide in a mixture can be at least, or be at most, 0.000000001%, 0.00000001%, 0.0000001%, 0.000001%, 0.00001%, 0.0001%, 0.001%, 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%. 
     In some embodiments, the percentage of the cellular component binding reagent not conjugated with a binding reagent oligonucleotide (e.g., a sample indexing oligonucleotide) in a mixture comprising a cellular component binding reagent conjugated with a binding reagent oligonucleotide (e.g., a sample indexing oligonucleotide) and the cellular component binding reagent that is not conjugated with the sample indexing oligonucleotide can be, or be about, 0.000000001%, 0.00000001%, 0.0000001%, 0.000001%, 0.00001%, 0.0001%, 0.001%, 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 3500, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, or a number or a range between any two of these values. In some embodiments, the percentage of the cellular component binding reagent not conjugated with a binding reagent oligonucleotide in a mixture can be at least, or be at most, 0.000000001%, 0.00000001%, 0.0000001%, 0.000001%, 0.00001%, 0.0001%, 0.001%, 0.01%, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% 40%, 41%, 42%, 43%, 44% 45% 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%. 
     Cellular Component Cocktails 
     In some embodiments, a cocktail of cellular component binding reagents (e.g., an antibody cocktail) can be used to increase labeling sensitivity in the methods disclosed herein. Without being bound by any particular theory, it is believed that this may be because cellular component expression or protein expression can vary between cell types and cell states, making finding a universal cellular component binding reagent or antibody that labels all cell types challenging. For example, cocktail of cellular component binding reagents can be used to allow for more sensitive and efficient labeling of more sample types. The cocktail of cellular component binding reagents can include two or more different types of cellular component binding reagents, for example a wider range of cellular component binding reagents or antibodies. Cellular component binding reagents that label different cellular component targets can be pooled together to create a cocktail that sufficiently labels all cell types, or one or more cell types of interest. 
     In some embodiments, each of the plurality of compositions (e.g., sample indexing compositions) comprises a cellular component binding reagent. In some embodiments, a composition of the plurality of compositions comprises two or more cellular component binding reagents, wherein each of the two or more cellular component binding reagents is associated with a binding reagent oligonucleotide (e.g., a sample indexing oligonucleotide), wherein at least one of the two or more cellular component binding reagents is capable of specifically binding to at least one of the one or more cellular component targets. The sequences of the binding reagent oligonucleotides associated with the two or more cellular component binding reagents can be identical. The sequences of the binding reagent oligonucleotides associated with the two or more cellular component binding reagents can comprise different sequences. Each of the plurality of compositions can comprise the two or more cellular component binding reagents. 
     The number of different types of cellular component binding reagents (e.g., a CD147 antibody and a CD47 antibody) in a composition can be different in different implementations. A composition with two or more different types of cellular component binding reagents can be referred to herein as a cellular component binding reagent cocktail (e.g., a sample indexing composition cocktail). The number of different types of cellular component binding reagents in a cocktail can vary. In some embodiments, the number of different types of cellular component binding reagents in cocktail can be, or be about 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, or a number or a range between any two of these values. In some embodiments, the number of different types of cellular component binding reagents in cocktail can be at least, or be at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, or 100000. The different types of cellular component binding reagents can be conjugated to binding reagent oligonucleotides with the same or different sequences (e.g., sample indexing sequences). 
     Methods of Quantitative Analysis of Cellular Component Targets 
     In some embodiments, the methods disclosed herein can also be used for quantitative analysis of a plurality of cellular component targets (for example, protein targets) in a sample using the compositions disclosed herein and oligonucleotide probes that can associate a barcode sequence (e.g., a molecular label sequence) to the oligonucleotides of the cellular component binding reagents (e.g., protein binding reagents). The oligonucleotides of the cellular component binding reagents can be, or comprise, an antibody oligonucleotide, a sample indexing oligonucleotide, a cell identification oligonucleotide, a control particle oligonucleotide, a control oligonucleotide, an interaction determination oligonucleotide, etc. In some embodiments, the sample can be a single cell, a plurality of cells, a tissue sample, a tumor sample, a blood sample, or the like. In some embodiments, the sample can comprise a mixture of cell types, such as normal cells, tumor cells, blood cells, B cells, T cells, maternal cells, fetal cells, etc., or a mixture of cells from different subjects. 
     In some embodiments, the sample can comprise a plurality of single cells separated into individual compartments, such as microwells in a microwell array. 
     In some embodiments, the binding target of the plurality of cellular component target (i.e., the cellular component target) can be, or comprise, a carbohydrate, a lipid, a protein, an extracellular protein, a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, a major histocompatibility complex, a tumor antigen, a receptor, an integrin, an intracellular protein, or any combination thereof. In some embodiments, the cellular component target is a protein target. In some embodiments, the plurality of cellular component targets comprises a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, an antibody, a major histocompatibility complex, a tumor antigen, a receptor, or any combination thereof. In some embodiments, the plurality of cellular component targets can comprise intracellular cellular components. In some embodiments, the plurality of cellular components can be at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 98%, at least 99%, or more, of all the encoded cellular components in an organism. In some embodiments, the plurality of cellular component targets can comprise at least 2, at least 3, at least 4, at least 5, at least 10, at least 20, at least 30, at least 40, at least 50, at least 100, at least 1000, at least 10000, or more different cellular component targets. 
     In some embodiments, the plurality of cellular component binding reagents is contacted with the sample for specific binding with the plurality of cellular component targets. Unbound cellular component binding reagents can be removed, for example, by washing. In embodiments where the sample comprises cells, any cellular component binding reagents not specifically bound to the cells can be removed. 
     In some instances, cells from a population of cells can be separated (e.g., isolated) into wells of a substrate of the disclosure. The population of cells can be diluted prior to separating. The population of cells can be diluted such that at least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, of wells of the substrate receive a single cell. The population of cells can be diluted such that at most 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, of wells of the substrate receive a single cell. The population of cells can be diluted such that the number of cells in the diluted population is, or is at least, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, of the number of wells on the substrate. The population of cells can be diluted such that the number of cells in the diluted population is, or is at least, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%, of the number of wells on the substrate. In some instances, the population of cells is diluted such that the number of cell is about 10% of the number of wells in the substrate. 
     Distribution of single cells into wells of the substrate can follow a Poisson distribution. For example, there can be at least a 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or more probability that a well of the substrate has more than one cell. There can be at least a 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or more probability that a well of the substrate has more than one cell. Distribution of single cells into wells of the substrate can be random. Distribution of single cells into wells of the substrate can be non-random. The cells can be separated such that a well of the substrate receives only one cell. 
     In some embodiments, the cellular component binding reagents can be additionally conjugated with fluorescent molecules to enable flow sorting of cells into individual compartments. 
     In some embodiments, the methods disclosed herein provide contacting a plurality of compositions with the sample for specific binding with the plurality of cellular component targets. It would be appreciated that the conditions used may allow specific binding of the cellular component binding reagents, e.g., antibodies, to the cellular component targets. Following the contacting step, unbound compositions can be removed. For example, in embodiments where the sample comprises cells, and the compositions specifically bind to cellular component targets are cell-surface cellular components, such as cell-surface proteins, unbound compositions can be removed by washing the cells with buffer such that only compositions that specifically bind to the cellular component targets remain with the cells. 
     In some embodiments, the methods disclosed herein can comprise associating an oligonucleotide (e.g., a barcode, or a stochastic barcode), including a barcode sequence (such as a molecular label), a cell label, a sample label, etc., or any combination thereof, to the plurality of oligonucleotides associated with the cellular component binding reagents. For example, a plurality of oligonucleotide probes comprising a barcode can be used to hybridize to the plurality of oligonucleotides of the compositions. 
     In some embodiments, the plurality of oligonucleotide probes can be immobilized on solid supports. The solid supports can be free floating, e.g., beads in a solution. The solid supports can be embedded in a semi-solid or solid array. In some embodiments, the plurality of oligonucleotide probes may not be immobilized on solid supports. When the plurality of oligonucleotide probes are in close proximity to the plurality associated with oligonucleotides of the cellular component binding reagents, the plurality of oligonucleotides of the cellular component binding reagents can hybridize to the oligonucleotide probes. The oligonucleotide probes can be contacted at a non-depletable ratio such that each distinct oligonucleotide of the cellular component binding reagents can associate with oligonucleotide probes having different barcode sequences (e.g., molecular labels) of the disclosure. 
     In some embodiments, the methods disclosed herein provide detaching the oligonucleotides from the cellular component binding reagents that are specifically bound to the cellular component targets. Detachment can be performed in a variety of ways to separate the chemical group from the cellular component binding reagent, such as UV photocleaving, chemical treatment (e.g., dithiothreitol treatment), heating, enzyme treatment, or any combination thereof. Detaching the oligonucleotide from the cellular component binding reagent can be performed either before, after, or during the step of hybridizing the plurality of oligonucleotide probes to the plurality of oligonucleotides of the compositions. 
     Methods of Simultaneous Quantitative Analysis of Cellular Component and Nucleic Acid Targets 
     In some embodiments, the methods disclosed herein can also be used for simultaneous quantitative analysis of a plurality of cellular component targets (e.g., protein targets) and a plurality of nucleic acid target molecules in a sample using the compositions disclosed herein and oligonucleotide probes that can associate a barcode sequence (e.g., a molecular label sequence) to both the oligonucleotides of the cellular component binding reagents and nucleic acid target molecules. Other methods of simultaneous quantitative analysis of a plurality of cellular component targets and a plurality of nucleic acid target molecules are described in U.S. Patent Application Publication Nos. US2018/0088112 and US2018/0346970; the content of each of these is incorporated herein by reference in its entirety. In some embodiments, the sample can be a single cell, a plurality of cells, a tissue sample, a tumor sample, a blood sample, or the like. In some embodiments, the sample can comprise a mixture of cell types, such as normal cells, tumor cells, blood cells, B cells, T cells, maternal cells, fetal cells, or a mixture of cells from different subjects. 
     In some embodiments, the sample can comprise a plurality of single cells separated into individual compartments, such as microwells in a microwell array. 
     In some embodiments, the plurality of cellular component targets comprises a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, an antibody, a major histocompatibility complex, a tumor antigen, a receptor, or any combination thereof. In some embodiments, the plurality of cellular component targets can comprise intracellular cellular components. In some embodiments, the plurality of cellular components can be, or be about, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99%, or a number or a range between any two of these values, of all the cellular components, such as expressed proteins, in an organism, or one or more cells of the organism. In some embodiments, the plurality of cellular components can be at least, or be at most, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, or 99%, of all the cellular components, such as proteins could be expressed, in an organism, or one or more cells of the organism. In some embodiments, the plurality of cellular component targets can comprise, or comprise about, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, 10000, or a number or a range between any two of these values, different cellular component targets. In some embodiments, the plurality of cellular component targets can comprise at least, or comprise at most, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, or 10000, different cellular component targets. 
     In some embodiments, the plurality of cellular component binding reagents is contacted with the sample for specific binding with the plurality of cellular component targets. Unbound cellular component binding reagents can be removed, for example, by washing. In embodiments where the sample comprises cells, any cellular component binding reagents not specifically bound to the cells can be removed. 
     In some instances, cells from a population of cells can be separated (e.g., isolated) into wells of a substrate of the disclosure. The population of cells can be diluted prior to separating. The population of cells can be diluted such that at least 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of wells of the substrate receive a single cell. The population of cells can be diluted such that at most 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of wells of the substrate receive a single cell. The population of cells can be diluted such that the number of cells in the diluted population is, or is at least, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the number of wells on the substrate. The population of cells can be diluted such that the number of cells in the diluted population is, or is at least, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of the number of wells on the substrate. In some instances, the population of cells is diluted such that the number of cell is about 10% of the number of wells in the substrate. 
     Distribution of single cells into wells of the substrate can follow a Poisson distribution. For example, there can be at least a 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or more probability that a well of the substrate has more than one cell. There can be at least a 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or more probability that a well of the substrate has more than one cell. Distribution of single cells into wells of the substrate can be random. Distribution of single cells into wells of the substrate can be non-random. The cells can be separated such that a well of the substrate receives only one cell. 
     In some embodiments, the cellular component binding reagents can be additionally conjugated with fluorescent molecules to enable flow sorting of cells into individual compartments. 
     In some embodiments, the methods disclosed herein provide contacting a plurality of compositions with the sample for specific binding with the plurality of cellular component targets. It would be appreciated that the conditions used may allow specific binding of the cellular component binding reagents, e.g., antibodies, to the cellular component targets. Following the contacting step, unbound compositions can be removed. For example, in embodiments where the sample comprises cells, and the compositions specifically bind to cellular component targets are on the cell surface, such as cell-surface proteins, unbound compositions can be removed by washing the cells with buffer such that only compositions that specifically bind to the cellular component targets remain with the cells. 
     In some embodiments, the methods disclosed herein can provide releasing the plurality of nucleic acid target molecules from the sample, e.g., cells. For example, the cells can be lysed to release the plurality of nucleic acid target molecules. Cell lysis may be accomplished by any of a variety of means, for example, by chemical treatment, osmotic shock, thermal treatment, mechanical treatment, optical treatment, or any combination thereof. Cells may be lysed by addition of a cell lysis buffer comprising a detergent (e.g., SDS, Li dodecyl sulfate, Triton X-100, Tween-20, or NP-40), an organic solvent (e.g., methanol or acetone), or digestive enzymes (e.g., proteinase K, pepsin, or trypsin), or any combination thereof. 
     It would be appreciated by one of ordinary skill in the art that the plurality of nucleic acid molecules can comprise a variety of nucleic acid molecules. In some embodiments, the plurality of nucleic acid molecules can comprise, DNA molecules, RNA molecules, genomic DNA molecules, mRNA molecules, rRNA molecules, siRNA molecules, or a combination thereof, and can be double-stranded or single-stranded. In some embodiments, the plurality of nucleic acid molecules comprises, or comprises about, 100, 1000, 10000, 20000, 30000, 40000, 50000, 100000, 1000000, or a number or a range between any two of these values, species. In some embodiments, the plurality of nucleic acid molecules comprises at least, or comprises at most, 100, 1000, 10000, 20000, 30000, 40000, 50000, 100000, or 1000000, species. In some embodiments, the plurality of nucleic acid molecules can be from a sample, such as a single cell, or a plurality of cells. In some embodiments, the plurality of nucleic acid molecules can be pooled from a plurality of samples, such as a plurality of single cells. 
     In some embodiments, the methods disclosed herein can comprise associating a barcode (e.g., a stochastic barcode), which can include a barcode sequence (such as a molecular label), a cell label, a sample label, or any combination thereof, to the plurality of nucleic acid target molecules and the plurality of oligonucleotides of the cellular component binding reagents. For example, a plurality of oligonucleotide probes comprising a stochastic barcode can be used to hybridize to the plurality of nucleic acid target molecules and the plurality of oligonucleotides of the compositions. 
     In some embodiments, the plurality of oligonucleotide probes can be immobilized on solid supports. The solid supports can be free floating, e.g., beads in a solution. The solid supports can be embedded in a semi-solid or solid array. In some embodiments, the plurality of oligonucleotide probes may not be immobilized on solid supports. When the plurality of oligonucleotide probes are in close proximity to the plurality of nucleic acid target molecules and the plurality of oligonucleotides of the cellular component binding reagents, the plurality of nucleic acid target molecules and the plurality of oligonucleotides of the cellular component binding reagents can hybridize to the oligonucleotide probes. The oligonucleotide probes can be contacted at a non-depletable ratio such that each distinct nucleic acid target molecules and oligonucleotides of the cellular component binding reagents can associate with oligonucleotide probes having different barcode sequences (e.g., molecular labels) of the disclosure. 
     In some embodiments, the methods disclosed herein provide detaching the oligonucleotides from the cellular component binding reagents that are specifically bound to the cellular component targets. Detachment can be performed in a variety of ways to separate the chemical group from the cellular component binding reagent, such as UV photocleaving, chemical treatment (e.g., dithiothreitol treatment), heating, enzyme treatment, or any combination thereof. Detaching the oligonucleotide from the cellular component binding reagent can be performed either before, after, or during the step of hybridizing the plurality of oligonucleotide probes to the plurality of nucleic acid target molecules and the plurality of oligonucleotides of the compositions. 
     Simultaneous Quantitative Analysis of Protein and Nucleic Acid Targets 
     In some embodiments, the methods disclosed herein also can be used for simultaneous quantitative analysis of multiple types of target molecules, for example protein and nucleic acid targets. For example, the target molecules can be, or comprise, cellular components.  FIG.  6    shows a schematic illustration of an exemplary method of simultaneous quantitative analysis of both nucleic acid targets and other cellular component targets (e.g., proteins) in single cells. In some embodiments, a plurality of compositions  605 ,  605   b ,  605   c , etc., each comprising a cellular component binding reagent, such as an antibody, is provided. Different cellular component binding reagents, such as antibodies, which bind to different cellular component targets are conjugated with different unique identifiers. Next, the cellular component binding reagents can be incubated with a sample containing a plurality of cells  610 . The different cellular component binding reagents can specifically bind to cellular components on the cell surface, such as a cell marker, a B-cell receptor, a T-cell receptor, an antibody, a major histocompatibility complex, a tumor antigen, a receptor, or any combination thereof. Unbound cellular component binding reagents can be removed, e.g., by washing the cells with a buffer. The cells with the cellular component binding reagents can be then separated into a plurality of compartments, such as a microwell array, wherein a single compartment  615  is sized to fit a single cell and a single bead  620 . Each bead can comprise a plurality of oligonucleotide probes, which can comprise a cell label that is common to all oligonucleotide probes on a bead, and barcode sequences (e.g., molecular label sequences). In some embodiments, each oligonucleotide probe can comprise a target binding region, for example, a poly(dT) sequence. The oligonucleotides  625  conjugated to the cellular component binding reagent can be detached from the cellular component binding reagent using chemical, optical or other means. The cell can be lysed  635  to release nucleic acids within the cell, such as genomic DNA or cellular mRNA  630 . Cellular mRNA  630 , oligonucleotides  625  or both can be captured by the oligonucleotide probes on bead  620 , for example, by hybridizing to the poly(dT) sequence. A reverse transcriptase can be used to extend the oligonucleotide probes hybridized to the cellular mRNA  630  and the oligonucleotides  625  using the cellular mRNA  630  and the oligonucleotides  625  as templates. The extension products produced by the reverse transcriptase can be subject to amplification and sequencing. Sequencing reads can be subject to demultiplexing of sequences or identifies of cell labels, barcodes (e.g., molecular labels), genes, cellular component binding reagent specific oligonucleotides (e.g., antibody specific oligonucleotides), etc., which can give rise to a digital representation of cellular components and gene expression of each single cell in the sample. 
     Association of Barcodes 
     The oligonucleotides associated with the cellular component binding reagents (e.g., antigen binding reagents or protein binding reagents) and/or the nucleic acid molecules may randomly associate with the oligonucleotide probes (e.g., barcodes, such as stochastic barcodes). The oligonucleotides associated with the cellular component binding reagents, referred to herein as binding reagent oligonucleotides, can be, or comprise oligonucleotides of the disclosure, such as an antibody oligonucleotide, a sample indexing oligonucleotide, a cell identification oligonucleotide, a control particle oligonucleotide, a control oligonucleotide, an interaction determination oligonucleotide, etc. Association can, for example, comprise hybridization of an oligonucleotide probe&#39;s target binding region to a complementary portion of the target nucleic acid molecule and/or the oligonucleotides of the protein binding reagents. For example, a oligo(dT) region of a barcode (e.g., a stochastic barcode) can interact with a poly(A) tail of a target nucleic acid molecule and/or a poly(A) tail of an oligonucleotide of a protein binding reagent. The assay conditions used for hybridization (e.g., buffer pH, ionic strength, temperature, etc.) can be chosen to promote formation of specific, stable hybrids. 
     The disclosure provides for methods of associating a molecular label with a target nucleic acid and/or an oligonucleotide associated with a cellular component binding reagent using reverse transcription. As a reverse transcriptase can use both RNA and DNA as template. For example, the oligonucleotide originally conjugated on the cellular component binding reagent can be either RNA or DNA bases, or both. A binding reagent oligonucleotide can be copied and linked (e.g., covalently linked) to a cell label and a barcode sequence (e.g., a molecular label) in addition to the sequence, or a portion thereof, of the binding reagent sequence. As another example, an mRNA molecule can be copied and linked (e.g., covalently linked) to a cell label and a barcode sequence (e.g., a molecular label) in addition to the sequence of the mRNA molecule, or a portion thereof. 
     In some embodiments, molecular labels can be added by ligation of an oligonucleotide probe target binding region and a portion of the target nucleic acid molecule and/or the oligonucleotides associated with (e.g., currently, or previously, associated with) with cellular component binding reagents. For example, the target binding region may comprise a nucleic acid sequence that can be capable of specific hybridization to a restriction site overhang (e.g., an EcoRI sticky-end overhang). The methods can further comprise treating the target nucleic acids and/or the oligonucleotides associated with cellular component binding reagents with a restriction enzyme (e.g., EcoRI) to create a restriction site overhang. A ligase (e.g., T4 DNA ligase) may be used to join the two fragments. 
     Determining the Number or Presence of Unique Molecular Label Sequences 
     In some embodiments, the methods disclosed herein comprise determining the number or presence of unique molecular label sequences for each unique identifier, each nucleic acid target molecule, and/or each binding reagent oligonucleotides (e.g., antibody oligonucleotides). For example, the sequencing reads can be used to determine the number of unique molecular label sequences for each unique identifier, each nucleic acid target molecule, and/or each binding reagent oligonucleotide. As another example, the sequencing reads can be used to determine the presence or absence of a molecular label sequence (such as a molecular label sequence associated with a target, a binding reagent oligonucleotide, an antibody oligonucleotide, a sample indexing oligonucleotide, a cell identification oligonucleotide, a control particle oligonucleotide, a control oligonucleotide, an interaction determination oligonucleotide, etc. in the sequencing reads). 
     In some embodiments, the number of unique molecular label sequences for each unique identifier, each nucleic acid target molecule, and/or each binding reagent oligonucleotide indicates the quantity of each cellular component target (e.g., an antigen target or a protein target) and/or each nucleic acid target molecule in the sample. In some embodiments, the quantity of a cellular component target and the quantity of its corresponding nucleic acid target molecules, e.g., mRNA molecules, can be compared to each other. In some embodiments, the ratio of the quantity of a cellular component target and the quantity of its corresponding nucleic acid target molecules, e.g., mRNA molecules, can be calculated. The cellular component targets can be, for example, cell surface protein markers. In some embodiments, the ratio between the protein level of a cell surface protein marker and the level of the mRNA of the cell surface protein marker is low. 
     The methods disclosed herein can be used for a variety of applications. For example, the methods disclosed herein can be used for proteome and/or transcriptome analysis of a sample. In some embodiments, the methods disclosed herein can be used to identify a cellular component target and/or a nucleic acid target, i.e., a biomarker, in a sample. In some embodiments, the cellular component target and the nucleic acid target correspond to each other, i.e., the nucleic acid target encodes the cellular component target. In some embodiments, the methods disclosed herein can be used to identify cellular component targets that have a desired ratio between the quantity of the cellular component target and the quantity of its corresponding nucleic acid target molecule in a sample, e.g., mRNA molecule. In some embodiments, the ratio is, or is about, 0.001, 0.01, 0.1, 1, 10, 100, 1000, or a number or a range between any two of the above values. In some embodiments, the ratio is at least, or is at most, 0.001, 0.01, 0.1, 1, 10, 100, or 1000. In some embodiments, the methods disclosed herein can be used to identify cellular component targets in a sample that the quantity of its corresponding nucleic acid target molecule in the sample is, or is about, 1000, 100, 10, 5, 2 1, 0, or a number or a range between any two of these values. In some embodiments, the methods disclosed herein can be used to identify cellular component targets in a sample that the quantity of its corresponding nucleic acid target molecule in the sample is more than, or less than, 1000, 100, 10, 5, 2 1, or 0. 
     Compositions and Kits 
     Some embodiments disclosed herein provide kits and compositions for simultaneous quantitative analysis of a plurality of cellular components (e.g., proteins) and/or a plurality of nucleic acid target molecules in a sample. The kits and compositions can, in some embodiments, comprise a plurality of cellular component binding reagents (e.g., a plurality of protein binding reagents) each conjugated with an oligonucleotide, wherein the oligonucleotide comprises a unique identifier for the cellular component binding reagent, and a plurality of oligonucleotide probes, wherein each of the plurality of oligonucleotide probes comprises a target binding region, a barcode sequence (e.g., a molecular label sequence), wherein the barcode sequence is from a diverse set of unique barcode sequences. In some embodiments, each of the oligonucleotides can comprise a molecular label, a cell label, a sample label, or any combination thereof. In some embodiments, each of the oligonucleotides can comprise a linker. In some embodiments, each of the oligonucleotides can comprise a binding site for an oligonucleotide probe, such as a poly(A) tail. For example, the poly(A) tail can be, e.g., oligodA 18  (unanchored to a solid support) or oligoA 18 V (anchored to a solid support). The oligonucleotides can comprise DNA residues, RNA residues, or both. 
     Disclosed herein include a plurality of sample indexing compositions. Each of the plurality of sample indexing compositions can comprise two or more cellular component binding reagents. Each of the two or more cellular component binding reagents can be associated with a sample indexing oligonucleotide. At least one of the two or more cellular component binding reagents can be capable of specifically binding to at least one cellular component target. The sample indexing oligonucleotide can comprise a sample indexing sequence for identifying sample origin of one or more cells of a sample. Sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions can comprise different sequences. 
     Disclosed herein include kits comprising sample indexing compositions for cell identification. In some embodiments. Each of two sample indexing compositions comprises a cellular component binding reagent (e.g., a protein binding reagent) associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of one or more cellular component targets (e.g., one or more protein targets), wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of the two sample indexing compositions comprise different sequences. In some embodiments, the sample indexing oligonucleotide comprises a molecular label sequence, a binding site for a universal primer, or a combination thereof. 
     Disclosed herein include kits for cell identification. In some embodiments, the kit comprises: two or more sample indexing compositions. Each of the two or more sample indexing compositions can comprise a cellular component binding reagent (e.g., an antigen binding reagent) associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of the two sample indexing compositions comprise different sequences. In some embodiments, the sample indexing oligonucleotide comprises a molecular label sequence, a binding site for a universal primer, or a combination thereof. Disclosed herein include kits for multiplet identification. In some embodiments, the kit comprises two sample indexing compositions. Each of two sample indexing compositions can comprise a cellular component binding reagent (e.g., an antigen binding reagent) associated with a sample indexing oligonucleotide, wherein the antigen binding reagent is capable of specifically binding to at least one of one or more cellular component targets (e.g., antigen targets), wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of the two sample indexing compositions comprise different sequences. 
     The unique identifiers (or oligonucleotides associated with cellular component binding reagents, such as binding reagent oligonucleotides, antibody oligonucleotides, sample indexing oligonucleotides, cell identification oligonucleotides, control particle oligonucleotides, control oligonucleotides, or interaction determination oligonucleotides) can have any suitable length, for example, from about 25 nucleotides to about 45 nucleotides long. In some embodiments, the unique identifier can have a length that is, is about, is less than, is greater than, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, 10 nucleotides, 15 nucleotides, 20 nucleotides, 25 nucleotides, 30 nucleotides, 35 nucleotides, 40 nucleotides, 45 nucleotides, 50 nucleotides, 55 nucleotides, 60 nucleotides, 70 nucleotides, 80 nucleotides, 90 nucleotides, 100 nucleotides, 200 nucleotides, or a range that is between any two of the above values. 
     In some embodiments, the unique identifiers are selected from a diverse set of unique identifiers. The diverse set of unique identifiers can comprise, or comprise about, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 5000, or a number or a range between any two of these values, different unique identifiers. The diverse set of unique identifiers can comprise at least, or comprise at most, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, or 5000, different unique identifiers. In some embodiments, the set of unique identifiers is designed to have minimal sequence homology to the DNA or RNA sequences of the sample to be analyzed. In some embodiments, the sequences of the set of unique identifiers are different from each other, or the complement thereof, by, or by about, 1 nucleotide, 2 nucleotides, 3 nucleotides, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, 10 nucleotides, or a number or a range between any two of these values. In some embodiments, the sequences of the set of unique identifiers are different from each other, or the complement thereof, by at least, or by at most, 1 nucleotide, 2 nucleotides, 3 nucleotides, 4 nucleotides, 5 nucleotides, 6 nucleotides, 7 nucleotides, 8 nucleotides, 9 nucleotides, or 10 nucleotides. 
     In some embodiments, the unique identifiers can comprise a binding site for a primer, such as universal primer. In some embodiments, the unique identifiers can comprise at least two binding sites for a primer, such as a universal primer. In some embodiments, the unique identifiers can comprise at least three binding sites for a primer, such as a universal primer. The primers can be used for amplification of the unique identifiers, for example, by PCR amplification. In some embodiments, the primers can be used for nested PCR reactions. 
     Any suitable cellular component binding reagents are contemplated in this disclosure, such as any protein binding reagents (e.g., antibodies or fragments thereof, aptamers, small molecules, ligands, peptides, oligonucleotides, etc., or any combination thereof). In some embodiments, the cellular component binding reagents can be polyclonal antibodies, monoclonal antibodies, recombinant antibodies, single-chain antibody (scAb), or fragments thereof, such as Fab, Fv, etc. In some embodiments, the plurality of protein binding reagents can comprise, or comprise about, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 5000, or a number or a range between any two of these values, different protein binding reagents. In some embodiments, the plurality of protein binding reagents can comprise at least, or comprise at most, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, or 5000, different protein binding reagents. 
     In some embodiments, the oligonucleotide is conjugated with the cellular component binding reagent through a linker. In some embodiments, the oligonucleotide can be conjugated with the protein binding reagent covalently. In some embodiment, the oligonucleotide can be conjugated with the protein binding reagent non-covalently. In some embodiments, the linker can comprise a chemical group that reversibly or irreversibly attached the oligonucleotide to the protein binding reagents. The chemical group can be conjugated to the linker, for example, through an amine group. In some embodiments, the linker can comprise a chemical group that forms a stable bond with another chemical group conjugated to the protein binding reagent. For example, the chemical group can be a UV photocleavable group, a disulfide bond, a streptavidin, a biotin, an amine, etc. In some embodiments, the chemical group can be conjugated to the protein binding reagent through a primary amine on an amino acid, such as lysine, or the N-terminus. The oligonucleotide can be conjugated to any suitable site of the protein binding reagent, as long as it does not interfere with the specific binding between the protein binding reagent and its protein target. In embodiments where the protein binding reagent is an antibody, the oligonucleotide can be conjugated to the antibody anywhere other than the antigen-binding site, for example, the Fc region, the C H 1 domain, the C H 2 domain, the C H 3 domain, the C L  domain, etc. In some embodiments, each protein binding reagent can be conjugated with a single oligonucleotide molecule. In some embodiments, each protein binding reagent can be conjugated with, or with about, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, or a number or a range between any two of these values, oligonucleotide molecules, wherein each of the oligonucleotide molecule comprises the same unique identifier. In some embodiments, each protein binding reagent can be conjugated with more than one oligonucleotide molecule, for example, at least, or at most, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, or 1000, oligonucleotide molecules, wherein each of the oligonucleotide molecule comprises the same unique identifier. 
     In some embodiments, the plurality of cellular component binding reagents (e.g., protein binding reagents) are capable of specifically binding to a plurality of cellular component targets (e.g., protein targets) in a sample. The sample can be, or comprise, a single cell, a plurality of cells, a tissue sample, a tumor sample, a blood sample, or the like. In some embodiments, the plurality of cellular component targets comprises a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, an antibody, a major histocompatibility complex, a tumor antigen, a receptor, or any combination thereof. In some embodiments, the plurality of cellular component targets can comprise intracellular proteins. In some embodiments, the plurality of cellular component targets can comprise intracellular proteins. In some embodiments, the plurality of cellular component targets can be, or be about, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, 99%, or a number or a range between any two of these values of all cellular component targets (e.g., proteins expressed or could be expressed) in an organism. In some embodiments, the plurality of cellular component targets can be at least, or be at most, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, or 99%, of all cellular component targets (e.g., proteins expressed or could be expressed) in an organism. In some embodiments, the plurality of cellular component targets can comprise, or comprise about, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, 10000, or a number or a range between any two of these values, different cellular component targets. In some embodiments, the plurality of cellular component targets can comprise at least, or comprise at most, 2, 3, 4, 5, 10, 20, 30, 40, 50, 100, 1000, or 10000, different cellular component targets. 
     Sample Indexing Using Oligonucleotide-Conjugated Cellular Component Binding Reagent 
     Disclosed herein include methods for sample identification. In some embodiments, the method comprises: contacting one or more cells from each of a plurality of samples with a sample indexing composition of a plurality of sample indexing compositions, wherein each of the one or more cells comprises one or more cellular component targets, wherein each of the plurality of sample indexing compositions comprises a cellular component binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences; removing unbound sample indexing compositions of the plurality of sample indexing compositions; barcoding (e.g., stochastically barcoding) the sample indexing oligonucleotides using a plurality of barcodes (e.g., stochastic barcodes) to create a plurality of barcoded sample indexing oligonucleotides; obtaining sequencing data of the plurality of barcoded sample indexing oligonucleotides; and identifying sample origin of at least one cell of the one or more cells based on the sample indexing sequence of at least one barcoded sample indexing oligonucleotide of the plurality of barcoded sample indexing oligonucleotides. 
     In some embodiments, barcoding the sample indexing oligonucleotides using the plurality of barcodes comprises: contacting the plurality of barcodes with the sample indexing oligonucleotides to generate barcodes hybridized to the sample indexing oligonucleotides; and extending the barcodes hybridized to the sample indexing oligonucleotides to generate the plurality of barcoded sample indexing oligonucleotides. Extending the barcodes can comprise extending the barcodes using a DNA polymerase to generate the plurality of barcoded sample indexing oligonucleotides. Extending the barcodes can comprise extending the barcodes using a reverse transcriptase to generate the plurality of barcoded sample indexing oligonucleotides. 
     An oligonucleotide-conjugated with an antibody, an oligonucleotide for conjugation with an antibody, or an oligonucleotide previously conjugated with an antibody is referred to herein as an antibody oligonucleotide (“AbOligo”). Antibody oligonucleotides in the context of sample indexing are referred to herein as sample indexing oligonucleotides. An antibody conjugated with an antibody oligonucleotide is referred to herein as a hot antibody or an oligonucleotide antibody. An antibody not conjugated with an antibody oligonucleotide is referred to herein as a cold antibody or an oligonucleotide free antibody. An oligonucleotide-conjugated with a binding reagent (e.g., a protein binding reagent), an oligonucleotide for conjugation with a binding reagent, or an oligonucleotide previously conjugated with a binding reagent is referred to herein as a reagent oligonucleotide. Reagent oligonucleotides in the context of sample indexing are referred to herein as sample indexing oligonucleotides. A binding reagent conjugated with an antibody oligonucleotide is referred to herein as a hot binding reagent or an oligonucleotide binding reagent. A binding reagent not conjugated with an antibody oligonucleotide is referred to herein as a cold binding reagent or an oligonucleotide free binding reagent. 
       FIG.  7    shows a schematic illustration of an exemplary workflow using oligonucleotide-associated cellular component binding reagents for sample indexing. In some embodiments, a plurality of compositions  705   a ,  705   b , etc., each comprising a binding reagent is provided. The binding reagent can be a protein binding reagent, such as an antibody. The cellular component binding reagent can comprise an antibody, a tetramer, an aptamer, a protein scaffold, or a combination thereof. The binding reagents of the plurality of compositions  705   a ,  705   b  can bind to an identical cellular component target. For example, the binding reagents of the plurality of compositions  705 ,  705   b  can be identical (except for the sample indexing oligonucleotides associated with the binding reagents). 
     Different compositions can include binding reagents conjugated with sample indexing oligonucleotides with different sample indexing sequences. The number of different compositions can be different in different implementations. In some embodiments, the number of different compositions can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, or a number or a range between any two of these values. In some embodiments, the number of different compositions can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or 10000. 
     In some embodiments, the sample indexing oligonucleotides of binding reagents in one composition can include an identical sample indexing sequence. The sample indexing oligonucleotides of binding reagents in one composition may not be identical. In some embodiments, the percentage of sample indexing oligonucleotides of binding reagents in one composition with an identical sample indexing sequence can be, or be about, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.9%, or a number or a range between any two of these values. In some embodiments, the percentage of sample indexing oligonucleotides of binding reagents in one composition with an identical sample indexing sequence can be at least, or be at most, 50%, 51%, 52%, 53%, 54% 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 99.9%. 
     The compositions  705   a  and  705   b  can be used to label samples of different samples. For example, the sample indexing oligonucleotides of the cellular component binding reagent in the composition  705   a  can have one sample indexing sequence and can be used to label cells  710   a , shown as black circles, in a sample  707   a , such as a sample of a patient. The sample indexing oligonucleotides of the cellular component binding reagents in the composition  705   b  can have another sample indexing sequence and can be used to label cells  710   b , shown as hatched circles, in a sample  707   b , such as a sample of another patient or another sample of the same patient. The cellular component binding reagents can specifically bind to cellular component targets or proteins on the cell surface, such as a cell marker, a B-cell receptor, a T-cell receptor, an antibody, a major histocompatibility complex, a tumor antigen, a receptor, or any combination thereof. Unbound cellular component binding reagents can be removed, e.g., by washing the cells with a buffer. 
     The cells with the cellular component binding reagents can be then separated into a plurality of compartments, such as a microwell array, wherein a single compartment  715   a ,  715   b  is sized to fit a single cell  710   a  and a single bead  720   a  or a single cell  710   b  and a single bead  720   b . Each bead  720   a ,  720   b  can comprise a plurality of oligonucleotide probes, which can comprise a cell label that is common to all oligonucleotide probes on a bead, and molecular label sequences. In some embodiments, each oligonucleotide probe can comprise a target binding region, for example, a poly(dT) sequence. The sample indexing oligonucleotides  725   a  conjugated to the cellular component binding reagent of the composition  705   a  can be configured to be (or can be) detachable or non-detachable from the cellular component binding reagent. The sample indexing oligonucleotides  725   a  conjugated to the cellular component binding reagent of the composition  705   a  can be detached from the cellular component binding reagent using chemical, optical or other means. The sample indexing oligonucleotides  725   b  conjugated to the cellular component binding reagent of the composition  705   b  can be configured to be (or can be) detachable or non-detachable from the cellular component binding reagent. The sample indexing oligonucleotides  725   b  conjugated to the cellular component binding reagent of the composition  705   b  can be detached from the cellular component binding reagent using chemical, optical or other means. 
     The cell  710   a  can be lysed to release nucleic acids within the cell  710   a , such as genomic DNA or cellular mRNA  730   a . The lysed cell  735   a  is shown as a dotted circle. Cellular mRNA  730   a , sample indexing oligonucleotides  725   a , or both can be captured by the oligonucleotide probes on bead  720   a , for example, by hybridizing to the poly(dT) sequence. A reverse transcriptase can be used to extend the oligonucleotide probes hybridized to the cellular mRNA  730   a  and the oligonucleotides  725   a  using the cellular mRNA  730   a  and the oligonucleotides  725   a  as templates. The extension products produced by the reverse transcriptase can be subject to amplification and sequencing. 
     Similarly, the cell  710   b  can be lysed to release nucleic acids within the cell  710   b , such as genomic DNA or cellular mRNA  730   b . The lysed cell  735   b  is shown as a dotted circle. Cellular mRNA  730   b , sample indexing oligonucleotides  725   b , or both can be captured by the oligonucleotide probes on bead  720   b , for example, by hybridizing to the poly(dT) sequence. A reverse transcriptase can be used to extend the oligonucleotide probes hybridized to the cellular mRNA  730   b  and the oligonucleotides  725   b  using the cellular mRNA  730   b  and the oligonucleotides  725   b  as templates. The extension products produced by the reverse transcriptase can be subject to amplification and sequencing. 
     Sequencing reads can be subject to demultiplexing of cell labels, molecular labels, gene identities, and sample identities (e.g., in terms of sample indexing sequences of sample indexing oligonucleotides  725   a  and  725   b ). Demultiplexing of cell labels, molecular labels, and gene identities can give rise to a digital representation of gene expression of each single cell in the sample. Demultiplexing of cell labels, molecular labels, and sample identities, using sample indexing sequences of sample indexing oligonucleotides, can be used to determine a sample origin. 
     In some embodiments, cellular component binding reagents against cellular component binding reagents on the cell surface can be conjugated to a library of unique sample indexing oligonucleotides to allow cells to retain sample identity. For example, antibodies against cell surface markers can be conjugated to a library of unique sample indexing oligonucleotides to allow cells to retain sample identity. This will enable multiple samples to be loaded onto the same Rhapsody™ cartridge as information pertaining sample source is retained throughout library preparation and sequencing. Sample indexing can allow multiple samples to be run together in a single experiment, simplifying and shortening experiment time, and eliminating batch effect. 
     Disclosed herein include methods for sample identification. In some embodiments, the method comprise: contacting one or more cells from each of a plurality of samples with a sample indexing composition of a plurality of sample indexing compositions, wherein each of the one or more cells comprises one or more cellular component targets, wherein each of the plurality of sample indexing compositions comprises a cellular component binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences; removing unbound sample indexing compositions of the plurality of sample indexing compositions. The method can include barcoding (e.g., stochastically barcoding) the sample indexing oligonucleotides using a plurality of barcodes (e.g., stochastic barcodes) to create a plurality of barcoded sample indexing oligonucleotides; obtaining sequencing data of the plurality of barcoded sample indexing oligonucleotides; and identifying sample origin of at least one cell of the one or more cells based on the sample indexing sequence of at least one barcoded sample indexing oligonucleotide of the plurality of barcoded sample indexing oligonucleotides. 
     In some embodiments, the method for sample identification comprises: contacting one or more cells from each of a plurality of samples with a sample indexing composition of a plurality of sample indexing compositions, wherein each of the one or more cells comprises one or more cellular component targets, wherein each of the plurality of sample indexing compositions comprises a cellular component binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences; removing unbound sample indexing compositions of the plurality of sample indexing compositions; and identifying sample origin of at least one cell of the one or more cells based on the sample indexing sequence of at least one sample indexing oligonucleotide of the plurality of sample indexing compositions. 
     In some embodiments, identifying the sample origin of the at least one cell comprises: barcoding (e.g., stochastically barcoding) sample indexing oligonucleotides of the plurality of sample indexing compositions using a plurality of barcodes (e.g., stochastic barcodes) to create a plurality of barcoded sample indexing oligonucleotides; obtaining sequencing data of the plurality of barcoded sample indexing oligonucleotides; and identifying the sample origin of the cell based on the sample indexing sequence of at least one barcoded sample indexing oligonucleotide of the plurality of barcoded sample indexing oligonucleotides. In some embodiments, barcoding the sample indexing oligonucleotides using the plurality of barcodes to create the plurality of barcoded sample indexing oligonucleotides comprises stochastically barcoding the sample indexing oligonucleotides using a plurality of stochastic barcodes to create a plurality of stochastically barcoded sample indexing oligonucleotides. 
     In some embodiments, identifying the sample origin of the at least one cell can comprise identifying the presence or absence of the sample indexing sequence of at least one sample indexing oligonucleotide of the plurality of sample indexing compositions. Identifying the presence or absence of the sample indexing sequence can comprise: replicating the at least one sample indexing oligonucleotide to generate a plurality of replicated sample indexing oligonucleotides; obtaining sequencing data of the plurality of replicated sample indexing oligonucleotides; and identifying the sample origin of the cell based on the sample indexing sequence of a replicated sample indexing oligonucleotide of the plurality of sample indexing oligonucleotides that correspond to the least one barcoded sample indexing oligonucleotide in the sequencing data. 
     In some embodiments, replicating the at least one sample indexing oligonucleotide to generate the plurality of replicated sample indexing oligonucleotides comprises: prior to replicating the at least one barcoded sample indexing oligonucleotide, ligating a replicating adaptor to the at least one barcoded sample indexing oligonucleotide. Replicating the at least one barcoded sample indexing oligonucleotide can comprise replicating the at least one barcoded sample indexing oligonucleotide using the replicating adaptor ligated to the at least one barcoded sample indexing oligonucleotide to generate the plurality of replicated sample indexing oligonucleotides. 
     In some embodiments, replicating the at least one sample indexing oligonucleotide to generate the plurality of replicated sample indexing oligonucleotides comprises: prior to replicating the at least one barcoded sample indexing oligonucleotide, contacting a capture probe with the at least one sample indexing oligonucleotide to generate a capture probe hybridized to the sample indexing oligonucleotide; and extending the capture probe hybridized to the sample indexing oligonucleotide to generate a sample indexing oligonucleotide associated with the capture probe. Replicating the at least one sample indexing oligonucleotide can comprise replicating the sample indexing oligonucleotide associated with the capture probe to generate the plurality of replicated sample indexing oligonucleotides. 
     Cell Overloading and Multiplet Identification 
     Also disclosed herein include methods, kits and systems for identifying cell overloading and multiplet. Such methods, kits and systems can be used in, or in combination with, any suitable methods, kits and systems disclosed herein, for example the methods, kits and systems for measuring cellular component expression level (such as protein expression level) using cellular component binding reagents associated with oligonucleotides. 
     Using current cell-loading technology, when about 20000 cells are loaded into a microwell cartridge or array with 60000 microwells, the number of microwells or droplets with two or more cells (referred to as doublets or multiplets) can be minimal. However, when the number of cells loaded increases, the number of microwells or droplets with multiple cells can increase significantly. For example, when about 50000 cells are loaded into about 60000 microwells of a microwell cartridge or array, the percentage of microwells with multiple cells can be quite high, such as 11-14%. Such loading of high number of cells into microwells can be referred to as cell overloading. However, if the cells are divided into a number of groups (e.g., 5), and cells in each group are labeled with sample indexing oligonucleotides with distinct sample indexing sequences, a cell label (e.g., a cell label of a barcode, such as a stochastic barcode) associated with two or more sample indexing sequences can be identified in sequencing data and removed from subsequent processing. In some embodiments, the cells are divided into a large number of groups (e.g., 10000), and cells in each group are labeled with sample indexing oligonucleotides with distinct sample indexing sequences, a sample label associated with two or more sample indexing sequences can be identified in sequencing data and removed from subsequent processing. In some embodiments, different cells are labeled with cell identification oligonucleotides with distinct cell identification sequences, a cell identification sequence associated with two or more cell identification oligonucleotides can be identified in sequencing data and removed from subsequent processing. Such higher number of cells can be loaded into microwells relative to the number of microwells in a microwell cartridge or array. 
     Disclosed herein include methods for sample identification. In some embodiments, the method comprises: contacting a first plurality of cells and a second plurality of cells with two sample indexing compositions respectively, wherein each of the first plurality of cells and each of the second plurality of cells comprise one or more cellular components, wherein each of the two sample indexing compositions comprises a cellular component binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular components, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of the two sample indexing compositions comprise different sequences; barcoding the sample indexing oligonucleotides using a plurality of barcodes to create a plurality of barcoded sample indexing oligonucleotides, wherein each of the plurality of barcodes comprises a cell label sequence, a barcode sequence (e.g., a molecular label sequence), and a target-binding region, wherein the barcode sequences of at least two barcodes of the plurality of barcodes comprise different sequences, and wherein at least two barcodes of the plurality of barcodes comprise an identical cell label sequence; obtaining sequencing data of the plurality of barcoded sample indexing oligonucleotides; and identifying one or more cell label sequences that is each associated with two or more sample indexing sequences in the sequencing data obtained; and removing the sequencing data associated with the one or more cell label sequences that is each associated with two or more sample indexing sequences from the sequencing data obtained and/or excluding the sequencing data associated with the one or more cell label sequences that is each associated with two or more sample indexing sequences from subsequent analysis (e.g., single cell mRNA profiling, or whole transcriptome analysis). In some embodiments, the sample indexing oligonucleotide comprises a barcode sequence (e.g., a molecular label sequence), a binding site for a universal primer, or a combination thereof. 
     For example, the method can be used to load 50000 or more cells (compared to 10000-20000 cells) using sample indexing. Sample indexing can use oligonucleotide-conjugated cellular component binding reagents (e.g., antibodies) or cellular component binding reagents against a cellular component (e.g., a universal protein marker) to label cells from different samples with a unique sample index. When two or more cells from different samples, two or more cells from different populations of cells of a sample, or two or more cells of a sample, are captured in the same microwell or droplet, the combined “cell” (or contents of the two or more cells) can be associated with sample indexing oligonucleotides with different sample indexing sequences (or cell identification oligonucleotides with different cell identification sequences). The number of different populations of cells can be different in different implementations. In some embodiments, the number of different populations can be, or be about, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any two of these values. In some embodiments, the number of different populations can be at least, or be at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. The number, or the average number, of cells in each population can be different in different implementations. In some embodiments, the number, or the average number, of cells in each population can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a number or a range between any two of these values. In some embodiments, the number, or the average number, of cells in each population can be at least, or be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100. When the number, or the average number, of cells in each population is sufficiently small (e.g., equal to, or fewer than, 50, 25, 10, 5, 4, 3, 2, or 1 cell(s) per population), the sample indexing composition for cell overloading and multiplet identification can be referred to as cell identification compositions. 
     Cells of a sample can be divided into multiple populations by aliquoting the cells of the sample into the multiple populations. A “cell” associated with more than one sample indexing sequence in the sequencing data can be identified as a “multiplet” based on two or more sample indexing sequences associated with one cell label sequence (e.g., a cell label sequence of a barcode, such as a stochastic barcode) in the sequencing data. The sequencing data of a combined “cell” is also referred to herein as a multiplet. A multiplet can be a doublet, a triplet, a quartet, a quintet, a sextet, a septet, an octet, a nonet, or any combination thereof. A multiplet can be any n-plet. In some embodiments, n is, or is about, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range between any two of these values. In some embodiments, n is at least, or is at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20. 
     When determining expression profiles of single cells, two cells may be identified as one cell and the expression profiles of the two cells may be identified as the expression profile for one cell (referred to as a doublet expression profile). For example, when determining expression profiles of two cells using barcoding (e.g., stochastic barcoding), the mRNA molecules of the two cells may be associated with barcodes having the same cell label. As another example, two cells may be associated with one particle (e.g., a bead). The particle can include barcodes with the same cell label. After lysing the cells, the mRNA molecules in the two cells can be associated with the barcodes of the particle, thus the same cell label. Doublet expression profiles can skew the interpretation of the expression profiles. 
     A doublet can refer to a combined “cell” associated with two sample indexing oligonucleotides with different sample indexing sequences. A doublet can also refer to a combined “cell” associated with sample indexing oligonucleotides with two sample indexing sequences. A doublet can occur when two cells associated with two sample indexing oligonucleotides of different sequences (or two or more cells associated with sample indexing oligonucleotides with two different sample indexing sequences) are captured in the same microwell or droplet, the combined “cell” can be associated with two sample indexing oligonucleotides with different sample indexing sequences. A triplet can refer to a combined “cell” associated with three sample indexing oligonucleotides all with different sample indexing sequences, or a combined“cell” associated with sample indexing oligonucleotides with three different sample indexing sequences. A quartet can refer to a combined “cell” associated with four sample indexing oligonucleotides all with different sample indexing sequences, or a combined “cell” associated with sample indexing oligonucleotides with four different sample indexing sequences. A quintet can refer to a combined “cell” associated with five sample indexing oligonucleotides all with different sample indexing sequences, or a combined “cell” associated with sample indexing oligonucleotides with five different sample indexing sequences. A sextet can refer to a combined “cell” associated with six sample indexing oligonucleotides all with different sample indexing sequences, or a combined“cell” associated with sample indexing oligonucleotides with six different sample indexing sequences. A septet can refer to a combined “cell” associated with seven sample indexing oligonucleotides all with different sample indexing sequences, or a combined “cell” associated with sample indexing oligonucleotides with seven different sample indexing sequences. An octet can refer to a combined“cell” associated with eight sample indexing oligonucleotides all with different sample indexing sequences, or a combined “cell” associated with sample indexing oligonucleotides with eight different sample indexing sequences. A nonet can refer to a combined “cell” associated with nine sample indexing oligonucleotides all with different sample indexing sequences, or a combined“cell” associated with sample indexing oligonucleotides with nine different sample indexing sequences. A multiplet can occur when two or more cells associated with two or more sample indexing oligonucleotides of different sequences (or two or more cells associated with sample indexing oligonucleotides with two or more different sample indexing sequences) are captured in the same microwell or droplet, the combined “cell” can be associated with sample indexing oligonucleotides with two or more different sample indexing sequences. 
     As another example, the method can be used for multiplet identification, whether in the context of sample overloading or in the context of loading cells onto microwells of a microwell array or generating droplets containing cells. When two or more cells are loaded into one microwell, the resulting data from the combined “cell” (or contents of the two or more cells) is a multiplet with aberrant gene expression profile. By using sample indexing, one can recognize some of these multiplets by looking for cell labels that are each associated with or assigned to two or more sample indexing oligonucleotides with different sample indexing sequences (or sample indexing oligonucleotides with two or more sample indexing sequences). With sample indexing sequence, the methods disclosed herein can be used for multiplet identification (whether in the context of sample overloading or not, or in the context of loading cells onto microwells of a microwell array or generating droplets containing cells). In some embodiments, the method comprises: contacting a first plurality of cells and a second plurality of cells with two sample indexing compositions respectively, wherein each of the first plurality of cells and each of the second plurality of cells comprise one or more cellular components, wherein each of the two sample indexing compositions comprises a cellular component binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular components, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of the two sample indexing compositions comprise different sequences; barcoding the sample indexing oligonucleotides using a plurality of barcodes to create a plurality of barcoded sample indexing oligonucleotides, wherein each of the plurality of barcodes comprises a cell label sequence, a barcode sequence (e.g., a molecular label sequence), and a target-binding region, wherein barcode sequences of at least two barcodes of the plurality of barcodes comprise different sequences, and wherein at least two barcodes of the plurality of barcodes comprise an identical cell label sequence; obtaining sequencing data of the plurality of barcoded sample indexing oligonucleotides; and identifying one or more multiplet cell label sequences that is each associated with two or more sample indexing sequences in the sequencing data obtained. 
     The number of cells that can be loaded onto microwells of a microwell cartridge or into droplets generated using a microfluidics device can be limited by the multiplet rate. Loading more cells can result in more multiplets, which can be hard to identify and create noise in the single cell data. With sample indexing, the method can be used to more accurately label or identify multiplets and remove the multiplets from the sequencing data or subsequent analysis. Being able to identify multiplets with higher confidence can increase user tolerance for the multiplet rate and load more cells onto each microwell cartridge or generating droplets with at least one cell each. 
     In some embodiments, contacting the first plurality of cells and the second plurality of cells with the two sample indexing compositions respectively comprises: contacting the first plurality of cells with a first sample indexing compositions of the two sample indexing compositions; and contacting the first plurality of cells with a second sample indexing compositions of the two sample indexing compositions. The number of pluralities of cells and the number of pluralities of sample indexing compositions can be different in different implementations. In some embodiments, the number of pluralities of cells and/or sample indexing compositions can be, or be about, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, 1000000, or a number or a range between any two of these values. In some embodiments, the number of pluralities of cells and/or sample indexing compositions can be at least, or be at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, or 1000000. The number of cells can be different in different implementations. In some embodiments, the number, or the average number, of cells can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, 1000000, or a number or a range between any two of these values. In some embodiments, the number, or the average number, or cells can be at least, or be at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, or 1000000. 
     In some embodiments, the method comprises: removing unbound sample indexing compositions of the two sample indexing compositions. Removing the unbound sample indexing compositions can comprise washing cells of the first plurality of cells and the second plurality of cells with a washing buffer. Removing the unbound sample indexing compositions can comprise selecting cells bound to at least one cellular component binding reagent of the two sample indexing compositions using flow cytometry. In some embodiments, the method comprises: lysing the one or more cells from each of the plurality of samples. 
     In some embodiments, the sample indexing oligonucleotide is configured to be (or can be) detachable or non-detachable from the cellular component binding reagent. The method can comprise detaching the sample indexing oligonucleotide from the cellular component binding reagent. Detaching the sample indexing oligonucleotide can comprise detaching the sample indexing oligonucleotide from the cellular component binding reagent by UV photocleaving, chemical treatment (e.g., using reducing reagent, such as dithiothreitol), heating, enzyme treatment, or any combination thereof. 
     In some embodiments, barcoding the sample indexing oligonucleotides using the plurality of barcodes comprises: contacting the plurality of barcodes with the sample indexing oligonucleotides to generate barcodes hybridized to the sample indexing oligonucleotides; and extending the barcodes hybridized to the sample indexing oligonucleotides to generate the plurality of barcoded sample indexing oligonucleotides. Extending the barcodes can comprise extending the barcodes using a DNA polymerase to generate the plurality of barcoded sample indexing oligonucleotides. Extending the barcodes can comprise extending the barcodes using a reverse transcriptase to generate the plurality of barcoded sample indexing oligonucleotides. 
     In some embodiments, the method comprises: amplifying the plurality of barcoded sample indexing oligonucleotides to produce a plurality of amplicons. Amplifying the plurality of barcoded sample indexing oligonucleotides can comprise amplifying, using polymerase chain reaction (PCR), at least a portion of barcode sequence (e.g., the molecular label sequence) and at least a portion of the sample indexing oligonucleotide. In some embodiments, obtaining the sequencing data of the plurality of barcoded sample indexing oligonucleotides can comprise obtaining sequencing data of the plurality of amplicons. Obtaining the sequencing data comprises sequencing at least a portion of the barcode sequence and at least a portion of the sample indexing oligonucleotide. In some embodiments, identifying the sample origin of the at least one cell comprises identifying sample origin of the plurality of barcoded targets based on the sample indexing sequence of the at least one barcoded sample indexing oligonucleotide. 
     In some embodiments, barcoding the sample indexing oligonucleotides using the plurality of barcodes to create the plurality of barcoded sample indexing oligonucleotides comprises stochastically barcoding the sample indexing oligonucleotides using a plurality of stochastic barcodes to create a plurality of stochastically barcoded sample indexing oligonucleotides. 
     In some embodiments, the method includes: barcoding a plurality of targets of the cell using the plurality of barcodes to create a plurality of barcoded targets, wherein each of the plurality of barcodes comprises a cell label sequence, and wherein at least two barcodes of the plurality of barcodes comprise an identical cell label sequence; and obtaining sequencing data of the barcoded targets. Barcoding the plurality of targets using the plurality of barcodes to create the plurality of barcoded targets can include: contacting copies of the targets with target-binding regions of the barcodes; and reverse transcribing the plurality targets using the plurality of barcodes to create a plurality of reverse transcribed targets. 
     In some embodiments, the method comprises: prior to obtaining the sequencing data of the plurality of barcoded targets, amplifying the barcoded targets to create a plurality of amplified barcoded targets. Amplifying the barcoded targets to generate the plurality of amplified barcoded targets can comprise: amplifying the barcoded targets by polymerase chain reaction (PCR). Barcoding the plurality of targets of the cell using the plurality of barcodes to create the plurality of barcoded targets can comprise stochastically barcoding the plurality of targets of the cell using a plurality of stochastic barcodes to create a plurality of stochastically barcoded targets. 
     In some embodiments, the method for cell identification comprise: contacting a first plurality of one or more cells and a second plurality of one or more cells with two cell identification compositions respectively, wherein each of the first plurality of one or more cells and each of the second plurality of one or more cells comprise one or more cellular components, wherein each of the two cell identification compositions comprises a cellular component binding reagent associated with a cell identification oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular components, wherein the cell identification oligonucleotide comprises a cell identification sequence, and wherein cell identification sequences of the two cell identification compositions comprise different sequences; barcoding the cell identification oligonucleotides using a plurality of barcodes to create a plurality of barcoded cell identification oligonucleotides, wherein each of the plurality of barcodes comprises a cell label sequence, a barcode sequence (e.g., a molecular label sequence), and a target-binding region, wherein the barcode sequences of at least two barcodes of the plurality of barcodes comprise different sequences, and wherein at least two barcodes of the plurality of barcodes comprise an identical cell label sequence; obtaining sequencing data of the plurality of barcoded cell identification oligonucleotides; and identifying one or more cell label sequences that is each associated with two or more cell identification sequences in the sequencing data obtained; and removing the sequencing data associated with the one or more cell label sequences that is each associated with two or more cell identification sequences from the sequencing data obtained and/or excluding the sequencing data associated with the one or more cell label sequences that is each associated with two or more cell identification sequences from subsequent analysis (e.g., single cell mRNA profiling, or whole transcriptome analysis). In some embodiments, the cell identification oligonucleotide comprises a barcode sequence (e.g., a molecular label sequence), a binding site for a universal primer, or a combination thereof. 
     A multiplet (e.g., doublet or triplet) can occur when two or more cells associated with two or more cell identification oligonucleotides of different sequences (or two or more cells associated with cell identification oligonucleotides with two or more different cell identification sequences) are captured in the same microwell or droplet, the combined “cell” can be associated with cell identification oligonucleotides with two or more different cell identification sequences. 
     Cell identification compositions can be used for multiplet identification, whether in the context of cell overloading or in the context of loading cells onto microwells of a microwell array or generating droplets containing cells. When two or more cells are loaded into one microwell, the resulting data from the combined “cell” (or contents of the two or more cells) is a multiplet with aberrant gene expression profile. By using cell identification, one can recognize some of these multiplets by looking for cell labels (e.g., cell labels of barcodes, such as stochastic barcodes) that are each associated with or assigned to two or more cell identification oligonucleotides with different cell identification sequences (or cell identification oligonucleotides with two or more cell identification sequences). With cell identification sequence, the methods disclosed herein can be used for multiplet identification (whether in the context of sample overloading or not, or in the context of loading cells onto microwells of a microwell array or generating droplets containing cells). In some embodiments, the method comprises: contacting a first plurality of one or more cells and a second plurality of one or more cells with two cell identification compositions respectively, wherein each of the first plurality of one or more cells and each of the second plurality of one or more cells comprise one or more cellular components, wherein each of the two cell identification compositions comprises a cellular component binding reagent associated with a cell identification oligonucleotide, wherein the cellular component binding reagent is capable of specifically binding to at least one of the one or more cellular components, wherein the cell identification oligonucleotide comprises a cell identification sequence, and wherein cell identification sequences of the two cell identification compositions comprise different sequences; barcoding the cell identification oligonucleotides using a plurality of barcodes to create a plurality of barcoded cell identification oligonucleotides, wherein each of the plurality of barcodes comprises a cell label sequence, a barcode sequence (e.g., a molecular label sequence), and a target-binding region, wherein barcode sequences of at least two barcodes of the plurality of barcodes comprise different sequences, and wherein at least two barcodes of the plurality of barcodes comprise an identical cell label sequence; obtaining sequencing data of the plurality of barcoded cell identification oligonucleotides; and identifying one or more multiplet cell label sequences that is each associated with two or more cell identification sequences in the sequencing data obtained. 
     The number of cells that can be loaded onto microwells of a microwell cartridge or into droplets generated using a microfluidics device can be limited by the multiplet rate. Loading more cells can result in more multiplets, which can be hard to identify and create noise in the single cell data. With cell identification, the method can be used to more accurately label or identify multiplets and remove the multiplets from the sequencing data or subsequent analysis. Being able to identify multiplets with higher confidence can increase user tolerance for the multiplet rate and load more cells onto each microwell cartridge or generating droplets with at least one cell each. 
     In some embodiments, contacting the first plurality of one or more cells and the second plurality of one or more cells with the two cell identification compositions respectively comprises: contacting the first plurality of one or more cells with a first cell identification compositions of the two cell identification compositions; and contacting the first plurality of one or more cells with a second cell identification compositions of the two cell identification compositions. The number of pluralities of cell identification compositions can be different in different implementations. In some embodiments, the number of cell identification compositions can be, or be about, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, 1000000, or a number or a range between any two of these values. In some embodiments, the number of cell identification compositions can be at least, or be at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, or 1000000. The number, or average number, of cells in each plurality of one or more cells can be different in different implementations. In some embodiments, the number, or average number, of cells in each plurality of one or more cells can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, 1000000, or a number or a range between any two of these values. In some embodiments, the number, or average number, of cells in each plurality of one or more cells can be at least, or be at most, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 10000, 100000, or 1000000. 
     In some embodiments, the method comprises: removing unbound cell identification compositions of the two cell identification compositions. Removing the unbound cell identification compositions can comprise washing cells of the first plurality of one or more cells and the second plurality of one or more cells with a washing buffer. Removing the unbound cell identification compositions can comprise selecting cells bound to at least one cellular component binding reagent of the two cell identification compositions using flow cytometry. In some embodiments, the method comprises: lysing the one or more cells from each of the plurality of samples. 
     In some embodiments, the cell identification oligonucleotide is configured to be (or can be) detachable or non-detachable from the cellular component binding reagent. The method can comprise detaching the cell identification oligonucleotide from the cellular component binding reagent. Detaching the cell identification oligonucleotide can comprise detaching the cell identification oligonucleotide from the cellular component binding reagent by UV photocleaving, chemical treatment (e.g., using reducing reagent, such as dithiothreitol), heating, enzyme treatment, or any combination thereof. 
     In some embodiments, barcoding the cell identification oligonucleotides using the plurality of barcodes comprises: contacting the plurality of barcodes with the cell identification oligonucleotides to generate barcodes hybridized to the cell identification oligonucleotides; and extending the barcodes hybridized to the cell identification oligonucleotides to generate the plurality of barcoded cell identification oligonucleotides. Extending the barcodes can comprise extending the barcodes using a DNA polymerase to generate the plurality of barcoded cell identification oligonucleotides. Extending the barcodes can comprise extending the barcodes using a reverse transcriptase to generate the plurality of barcoded cell identification oligonucleotides. 
     In some embodiments, the method comprises: amplifying the plurality of barcoded cell identification oligonucleotides to produce a plurality of amplicons. Amplifying the plurality of barcoded cell identification oligonucleotides can comprise amplifying, using polymerase chain reaction (PCR), at least a portion of barcode sequence (e.g., the molecular label sequence) and at least a portion of the cell identification oligonucleotide. In some embodiments, obtaining the sequencing data of the plurality of barcoded cell identification oligonucleotides can comprise obtaining sequencing data of the plurality of amplicons. Obtaining the sequencing data comprises sequencing at least a portion of the barcode sequence and at least a portion of the cell identification oligonucleotide. In some embodiments, identifying the sample origin of the at least one cell comprises identifying sample origin of the plurality of barcoded targets based on the cell identification sequence of the at least one barcoded cell identification oligonucleotide. 
     In some embodiments, barcoding the cell identification oligonucleotides using the plurality of barcodes to create the plurality of barcoded cell identification oligonucleotides comprises stochastically barcoding the cell identification oligonucleotides using a plurality of stochastic barcodes to create a plurality of stochastically barcoded cell identification oligonucleotides. 
     Oligonucleotide-Conjugated Antibodies 
     Unique Molecular Label Sequence 
     In some embodiments, the methods and compositions provided herein comprise an oligonucleotide associated with a cellular component-binding reagent (e.g., antibody oligonucleotide (“AbOligo” or “AbO”), binding reagent oligonucleotide, cellular component-binding reagent specific oligonucleotides, sample indexing oligonucleotides) as described in U.S. Application No. 62/796,018, filed on Jan. 23, 2019, the content of which is incorporated herein by reference in its entirety. In some embodiments, the oligonucleotide associated with a cellular component-binding reagent (e.g., antibody oligonucleotide (“AbOligo” or “AbO”), binding reagent oligonucleotide, cellular component-binding reagent specific oligonucleotides, sample indexing oligonucleotides) comprises a unique molecular label sequence (also referred to as a molecular index (MI), “molecular barcode,” or Unique Molecular Identifier (UMI)). In some embodiments, binding reagent oligonucleotide species comprising molecule barcodes as described herein reduce bias by increasing sensitivity, decreasing relative standard error, or increasing sensitivity and/or reducing standard error. The molecule barcode can comprise a unique sequence, so that when multiple sample nucleic acids (which can be the same and/or different from each other) are associated one-to-one with molecule barcodes, different sample nucleic acids can be differentiated from each other by the molecule barcodes. As such, even if a sample comprises two nucleic acids having the same sequence, each of these two nucleic acids can be labeled with a different molecule barcode, so that nucleic acids in the population can be quantified, even after amplification. The molecule barcode can comprise a nucleic acid sequence of at least 5 nucleotides, for example at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides, including ranges between any two of the listed values, for example 5-50, 5-45, 5-40, 5-35, 5-30, 5-25, 5-20, 5-15, 5-14, 5-13, 5-12, 5-11, 5-10, 5-9, 5-8, 5-7, 5-6, 6-50, 6-45, 6-40, 6-35, 6-30, 6-25, 6-20, 6-15, 6-14, 6-13, 6-12, 6-11, 6-10, 6-9, 6-8, 6-7, 7-50, 7-45, 7-40, 7-35, 7-30, 7-25, 7-20, 7-15, 7-14, 7-13, 7-12, 7-11, 7-10, 7-9, 7-8, 8-50, 8-45, 8-40, 8-35, 8-30, 8-25, 8-20, 8-15, 8-14, 8-13, 8-12, 8-11, 8-10, 8-9, 9-50, 9-45, 9-40, 9-35, 9-30, 9-25, 9-20, 9-15, 9-14, 9-13, 9-12, 9-11, 9-10, 10-50, 10-45, 10-40, 10-35, 10-30, 10-25, 10-20, 10-15, 10-14, 10-13, 10-12, or 10-11 nucleotides. In some embodiments, the nucleic acid sequence of the molecule barcode comprises a unique sequence, for example, so that each unique oligonucleotide species in a composition comprises a different molecule barcode. In some embodiments, two or more unique oligonucleotide species can comprise the same molecule barcode, but still differ from each other. For example, if the unique oligonucleotide species include sample barcodes, each unique oligonucleotide species with a particular sample barcode can comprise a different molecule barcode. In some embodiments, a composition comprising unique oligonucleotide species comprises a molecule barcode diversity of at least 1000 different molecule barcodes, and thus at least 1000 unique oligonucleotide species. In some embodiments, a composition comprising unique oligonucleotide species comprises a molecule barcode diversity of at least 6500 different molecule barcodes, and thus at least 6500 unique oligonucleotide species. In some embodiments, a composition comprising unique oligonucleotide species comprises a molecule barcode diversity of at least 65000 different molecule barcodes, and thus at least 65,000 unique oligonucleotide species. 
     In some embodiments, the unique molecular label sequence is positioned 5′ of the unique identifier sequence without any intervening sequences between the unique molecular label sequence and the unique identifier sequence. In some embodiments, the unique molecular label sequence is positioned 5′ of a spacer, which is positioned 5′ of the unique identifier sequence, so that a spacer is between the unique molecular label sequence and the unique identifier sequence. In some embodiments, the unique identifier sequence is positioned 5′ of the unique molecular label sequence without any intervening sequences between the unique identifier sequence and the unique molecular label sequence. In some embodiments, the unique identifier sequence is positioned 5′ of a spacer, which is positioned 5′ of the unique molecular label sequence, so that a spacer is between the unique identifier sequence and the unique molecular label sequence. 
     The unique molecular label sequence can comprise a nucleic acid sequence of at least 3 nucleotides, for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 nucleotides, including ranges between any two of the listed values, for example 3-50, 3-45, 3-40, 3-35, 3-30, 3-25, 3-20, 3-15, 3-14, 3-13, 3-12, 3-11, 3-10, 3-9, 3-8, 3-7, 3-6, 3-5, 3-4, 4-50, 4-45, 4-40, 4-35, 4-30, 4-25, 4-20, 4-15, 4-14, 4-13, 4-12, 4-11, 4-10, 4-9, 4-8, 4-7, 4-6, 4-5, 5-50, 5-45, 5-40, 5-35, 5-30, 5-25, 5-20, 5-15, 5-14, 5-13, 5-12, 5-11, 5-10, 5-9, 5-8, 5-7, 5-6, 6-50, 6-45, 6-40, 6-35, 6-30, 6-25, 6-20, 6-15, 6-14, 6-13, 6-12, 6-11, 6-10, 6-9, 6-8, 6-7, 7-50, 7-45, 7-40, 7-35, 7-30, 7-25, 7-20, 7-15, 7-14, 7-13, 7-12, 7-11, 7-10, 7-9, 7-8, 8-50, 8-45, 8-40, 8-35, 8-30, 8-25, 8-20, 8-15, 8-14, 8-13, 8-12, 8-11, 8-10, 8-9, 9-50, 9-45, 9-40, 9-35, 9-30, 9-25, 9-20, 9-15, 9-14, 9-13, 9-12, 9-11, 9-10, 10-50, 10-45, 10-40, 10-35, 10-30, 10-25, 10-20, 10-15, 10-14, 10-13, 10-12, or 10-11 nucleotides. In some embodiments, the unique molecular label sequence is 2-20 nucleotides in length. 
     In some embodiments, the unique molecular label sequence of the binding reagent oligonucleotide comprises the sequence of at least three repeats of the doublets “VN” and/or “NV” (in which each “V” is any of A, C, or G, and in which “N” is any of A, G, C, or T), for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. Examples of multiple repeats of the doublet “VN” include VN, VNVN, VNVNVN, and VNVNVNVN. It is noted that while the formulas “VN” and “NV” describe constraints on the base content, not every V or every N has to be the same or different. For example, if the molecule barcodes of unique oligonucleotide species in a composition comprised VNVNVN, one molecule barcode can comprise the sequence ACGGCA, while another molecule barcode can comprise the sequence ATACAT, while another molecule barcode could comprise the sequence ATACAC. It is noted that any number of repeats of the doublet “VN” would have a T content of no more than 50%. In some embodiments, at least 95% of the unique oligonucleotide species of a composition comprising at least 1000 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 99% of the unique oligonucleotide species of a composition comprising at least 1000 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 99.9% of the unique oligonucleotide species of a composition comprising at least 1000 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 95% of the unique oligonucleotide species of a composition comprising at least 6500 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 99% of the unique oligonucleotide species of a composition comprising at least 6500 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 99.9% of the unique oligonucleotide species of a composition comprising at least 6500 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 95% of the unique oligonucleotide species of a composition comprising at least 65,000 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 99% of the unique oligonucleotide species of a of composition comprising at least 65,000 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, at least 99.9% of the unique oligonucleotide species of a composition comprising at least 65,000 unique oligonucleotide species comprise molecule barcodes comprising at least three repeats of the doublets “VN” and/or “NV,” for example at least 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 repeats, including ranges between any two of the listed values. In some embodiments, the composition consists of or consists essentially of at least 1000, 6500, or 65,000 unique oligonucleotide species that each have a molecule barcode comprising the sequence VNVNVN. In some embodiments, the composition consists of or consists essentially of at least 1000, 6500, or 65000 unique oligonucleotide species that each has a molecule barcode comprising the sequence VNVNVNVN. In some embodiments, at least 95%, 99%, or 99.9% of the barcode regions of the composition as described herein comprise at least three repeats of the doublets “VN” and/or “NV,” as described herein. In some embodiments, unique molecular label sequences comprising repeated “doublets “VN” and/or “NV” can yield low bias, while providing a compromise between reducing bias and maintaining a relatively large quantity of available nucleotide sequences, so that relatively high diversity can be obtained in a relatively short sequence, while still minimizing bias. In some embodiments, unique molecular label sequences comprising repeated “doublets “VN” and/or “NV” can reduce bias by increasing sensitivity, decreasing relative standard error, or increasing sensitivity and reducing standard error. In some embodiments, unique molecular label sequences comprising repeated “doublets “VN” and/or “NV” improve informatics analysis by serving as a geomarker. In some embodiments, the repeated doublets “VN” and/or “NV” described herein reduce the incidence of homopolymers within the unique molecular label sequences. In some embodiments, the repeated doublets “VN” and/or “NV” described herein break up homopolymers. 
     In some embodiments, the sample indexing oligonucleotide comprises a first molecular label sequence. In some embodiments, the first molecular label sequences of at least two sample indexing oligonucleotides are different, and the sample indexing sequences of the at least two sample indexing oligonucleotides are identical. In some embodiments, the first molecular label sequences of at least two sample indexing oligonucleotides are different, and the sample indexing sequences of the at least two sample indexing oligonucleotides are different. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a second molecular label sequence. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are identical. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are different. In some embodiments, the number of unique second molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. In some embodiment, a combination (e.g., minimum, average, and maximum) of (1) the number of unique first molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data and (2) the number of unique second molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. 
     Alignment Sequence 
     In some embodiments, the binding reagent oligonucleotide comprises an alignment sequence (e.g., the alignment sequence  825   bb  described with reference to  FIG.  9   ) adjacent to the poly(dA) region. The alignment sequence can be 1 or more nucleotides in length. The alignment sequence can be 2 nucleotides in length. The alignment sequence can comprise a guanine, a cytosine, a thymine, a uracil, or a combination thereof. The alignment sequence can comprise a poly(dT) region, a poly(dG) region, a poly(dC) region, a poly(dU) region, or a combination thereof. In some embodiments, the alignment sequence is 5′ to the poly(dA) region. Advantageously, in some embodiments, the presence of the alignment sequence enables the poly(A) tail of each of the binding reagent oligonucleotides to have the same length, leading to greater uniformity of performance. In some embodiments, the percentage of binding reagent oligonucleotides with an identical poly(dA) region length within a plurality of binding reagent oligonucleotides, each of which comprise an alignment sequence, can be, or be about, 80%, 90%, 91%, 93%, 95%, 97%, 99.9%, 99.9%, 99.99%, or 100%, or a number or a range between any two of these values. In some embodiments, the percentage of binding reagent oligonucleotides with an identical poly(dA) region length within the plurality of binding reagent oligonucleotides, each of which comprise an alignment sequence, can be at least, or be at most, 80%, 90%, 91%, 93%, 95%, 97%, 99.9%, 99.9%, 99.99%, or 100%. 
     The length of the alignment sequence can be different in different implementations. In some embodiments, the length of the alignment sequence can be, or can be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, or a number or a range between any two of these values. In some embodiments, the length of the alignment sequence can be at least, or can be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100. The number of guanine(s), cytosine(s), thymine(s), or uracil(s) in the alignment sequence can be different in different implementations. The number of guanine(s), cytosine(s), thymine(s), or uracil(s) can be, or can be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, or a number or a range between any two of these values. The number of guanine(s), cytosine(s), thymine(s), or uracil(s) can be at least, or can be at most, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100. In some embodiments, the sample indexing oligonucleotide comprises an alignment sequence. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises an alignment sequence. 
     Linker 
     The binding reagent oligonucleotide can be conjugated with the cellular component binding reagent through various mechanisms. In some embodiments, the binding reagent oligonucleotide can be conjugated with the cellular component binding reagent covalently. In some embodiments, the binding reagent oligonucleotide can be conjugated with the cellular component binding reagent non-covalently. In some embodiments, the binding reagent oligonucleotide is conjugated with the cellular component binding reagent through a linker. In some embodiments, the binding reagent oligonucleotide can comprise the linker. The linker can comprise a chemical group. The chemical group can be reversibly, or irreversibly, attached to the molecule of the cellular component binding reagent. The chemical group can be selected from the group consisting of a UV photocleavable group, a disulfide bond, a streptavidin, a biotin, an amine, and any combination thereof. The linker can comprise a carbon chain. The carbon chain can comprise, for example, 5-50 carbon atoms. The carbon chain can have different numbers of carbon atoms in different embodiments. In some embodiments, the number of carbon atoms in the carbon chain can be, or can be about, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, or a number or a range between any two of these values. In some embodiments, the number of carbon atoms in the carbon chain can be at least, or can be at most, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50. In some embodiments, the carbon chain comprises 2-30 carbons. In some embodiments, the carbon chain comprises 12 carbons. In some embodiments, amino modifiers employed for binding reagent oligonucleotide can be conjugated to the cellular component binding reagent. In some embodiments, the linker comprises 5′ amino modifier C6 (5AmMC6). In some embodiments, the linker comprises 5′ amino modifier C12 (5AmMC12). In some embodiments, the linker comprises a derivative of 5AmMC12. In some embodiments, a longer linker achieves a higher efficiency of conjugation. In some embodiments, a longer linker achieves a higher efficiency of modification prior to conjugation. In some embodiments, increasing the distance between the functional amine and the DNA sequence yields a higher efficiency of conjugation. In some embodiments, increasing the distance between the functional amine and the DNA sequence yields a higher efficiency of modification prior to conjugation. In some embodiments, the use of 5AmMC12 as a linker yields a higher efficiency of modification (prior to conjugation) than the use of 5AmMC6 as a linker. In some embodiments the use of 5AmMC12 as a linker yields a higher efficiency of conjugation than the use of 5AmMC6 as a linker. In some embodiments, the sample indexing oligonucleotide is associated with the cellular component-binding reagent through a linker. In some embodiments, the cellular component-binding reagent specific oligonucleotide is associated with the cellular component-binding reagent through a linker. 
     Antibody-Specific Barcode Sequence 
     Disclosed herein, in several embodiments, are improvements to the design of the unique identifier sequence (e.g., antibody-specific barcode sequence) of a binding reagent oligonucleotide. In some embodiments the unique identifier sequence (e.g, sample indexing sequence, cellular component-binding reagent specific oligonucleotide) is designed to have a Hamming distance greater than 3. In some embodiments, the Hamming distance of the unique identifier sequence can be, or be about, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a number or a range between any two of these values. In some embodiments, the unique identifier sequences has a GC content in the range of 40% to 60% and does not have a predicted secondary structure (e.g., hairpin). In some embodiments, the unique identifier sequence does not comprise any sequences predicted in silico to bind to the mouse and/or human transcripts. In some embodiments, the unique identifier sequence does not comprise any sequences predicted in silico to bind to Rhapsody and/or SCMK system primers. In some embodiments, the unique identifier sequence does not comprise homopolymers. 
     Primer Adapter 
     In some embodiments, the binding reagent oligonucleotide comprises a primer adapter. In some embodiments, the primer adapter comprises the sequence of a first universal primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof. In some embodiments, the first universal primer comprises an amplification primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof. In some embodiments, the first universal primer comprises a sequencing primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof. In some embodiments, the sequencing primer comprises an Illumina sequencing primer. In some embodiments, the sequencing primer comprises a portion of an Illumina sequencing primer. In some embodiments, the sequencing primer comprises a P7 sequencing primer. In some embodiments, the sequencing primer comprises a portion of P7 sequencing primer. In some embodiments, the primer adapter comprises an adapter for Illumina P7. In some embodiments, the primer adapter comprises a partial adapter for Illumina P7. In some embodiments, the amplification primer is an Illumina P7 sequence or a subsequence thereof. In some embodiments, the sequencing primer is an Illumina R2 sequence or a subsequence thereof. In some embodiments, the first universal primer is 5-50 nucleotides in length. In some embodiments, The primer adapter can comprise a nucleic acid sequence of at least 5 nucleotides, for example at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides, including ranges between any two of the listed values, for example 5-50, 5-45, 5-40, 5-35, 5-30, 5-25, 5-20, 5-15, 5-14, 5-13, 5-12, 5-11, 5-10, 5-9, 5-8, 5-7, 5-6, 6-50, 6-45, 6-40, 6-35, 6-30, 6-25, 6-20, 6-15, 6-14, 6-13, 6-12, 6-11, 6-10, 6-9, 6-8, 6-7, 7-50, 7-45, 7-40, 7-35, 7-30, 7-25, 7-20, 7-15, 7-14, 7-13, 7-12, 7-11, 7-10, 7-9, 7-8, 8-50, 8-45, 8-40, 8-35, 8-30, 8-25, 8-20, 8-15, 8-14, 8-13, 8-12, 8-11, 8-10, 8-9, 9-50, 9-45, 9-40, 9-35, 9-30, 9-25, 9-20, 9-15, 9-14, 9-13, 9-12, 9-11, 9-10, 10-50, 10-45, 10-40, 10-35, 10-30, 10-25, 10-20, 10-15, 10-14, 10-13, 10-12, or 10-11 nucleotides. The primer adapter can comprise a nucleic acid sequence of at least 5 nucleotides of the sequence of a first universal primer, an amplification primer, a sequencing primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof, for example at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 nucleotides, including ranges between any two of the listed values, for example 5-50, 5-45, 5-40, 5-35, 5-30, 5-25, 5-20, 5-15, 5-14, 5-13, 5-12, 5-11, 5-10, 5-9, 5-8, 5-7, 5-6, 6-50, 6-45, 6-40, 6-35, 6-30, 6-25, 6-20, 6-15, 6-14, 6-13, 6-12, 6-11, 6-10, 6-9, 6-8, 6-7, 7-50, 7-45, 7-40, 7-35, 7-30, 7-25, 7-20, 7-15, 7-14, 7-13, 7-12, 7-11, 7-10, 7-9, 7-8, 8-50, 8-45, 8-40, 8-35, 8-30, 8-25, 8-20, 8-15, 8-14, 8-13, 8-12, 8-11, 8-10, 8-9, 9-50, 9-45, 9-40, 9-35, 9-30, 9-25, 9-20, 9-15, 9-14, 9-13, 9-12, 9-11, 9-10, 10-50, 10-45, 10-40, 10-35, 10-30, 10-25, 10-20, 10-15, 10-14, 10-13, 10-12, or 10-11 nucleotides of the sequence of a first universal primer, an amplification primer, a sequencing primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof. 
     A conventional amplification workflow for sequencing library preparation can employ three rounds of PCR, such as, for example: a first round (“PCR 1”) employing a target-specific primer and a primer against the universal Illumina sequencing primer 1 sequence; a second round (“PCR 2”) using a nested target-specific primer flanked by Illumina sequencing primer 2 sequence, and a primer against the universal Illumina sequencing primer 1 sequence; and a third round (“PCR 3”) adding Illumina P5 and P7 and sample index. Advantageously, in some embodiments, the primer adapter disclosed herein enables a shorter and simpler workflow in library preparation as compared to if the starting template (e.g., a sample indexing oligonucleotide attached to a bead) does not have a primer adapter. In some embodiments, the primer adapter reduces pre-sequencing PCR amplification of a template by one round (as compared to if the template does not comprise a primer adapter). In some embodiments, the primer adapter reduces pre-sequencing PCR amplification of the template to one round (as compared to if the template does not comprise a primer adapter). In some embodiments, a template comprising the primer adapter does not require a PCR amplification step for attachment of Illumina sequencing adapters that would require pre-sequencing if the template did not comprise a primer adapter. In some embodiments, the primer adapter sequence (or a subsequence thereof) is not part of the sequencing readout of a sequencing template comprising a primer adapter sequence and therefore does not affect read quality of a template comprising a primer adapter. In some embodiments, a template comprising the primer adapter has decreased sequencing diversity as compared to if the template does not comprise a primer adapter. 
     In some embodiments, the sample indexing oligonucleotide comprises a primer adapter. In some embodiments, replicating a sample indexing oligonucleotide, a barcoded sample indexing oligonucleotide, or a product thereof, comprises using a first universal primer, a first primer comprising the sequence of the first universal primer, or a combination thereof, to generate a plurality of replicated sample indexing oligonucleotides. In some embodiments, replicating a one sample indexing oligonucleotide, a barcoded sample indexing oligonucleotide, or a product thereof, comprises using a first universal primer, a first primer comprising the sequence of the first universal primer, a second universal primer, a second primer comprising the sequence of the second universal primer, or a combination thereof, to generate the plurality of replicated sample indexing oligonucleotides. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises a primer adapter. In some embodiments, the cellular component-binding reagent specific oligonucleotide comprises the sequence of a first universal primer, a complementary sequence thereof, a partial sequence thereof, or a combination thereof 
     Binding Reagent Oligonucleotide Barcoding 
       FIG.  8    shows a schematic illustration of a non-limiting exemplary workflow of barcoding of a binding reagent oligonucleotide  825  (antibody oligonucleotide illustrated here) that is associated with a binding reagent  805  (antibody illustrated here). The binding reagent oligonucleotide  825  can be associated with binding reagent  805  through linker  825   l . The binding reagent oligonucleotide  825  can be detached from the binding reagent using chemical, optical or other means. The binding reagent oligonucleotide  825  can be an mRNA mimic. The binding reagent oligonucleotide  825  can include a primer adapter  825   pa , an antibody molecular label  825   am  (e.g., a unique molecular label sequence), an antibody barcode  825   ab  (e.g., a unique identifier sequence), an alignment sequence  825   bb , and a poly(A) tail  825   a . In some embodiments, the primer adapter  825   pa  comprises the sequence of a first universal primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof. In some embodiments, the primer adapter  825   pa  can be the same for all or some of binding reagent oligonucleotides  825 . In some embodiments, the antibody barcode  825   ab  can be the same for all or some of binding reagent oligonucleotides  825 . In some embodiments, the antibody barcode  825   ab  of different binding reagent oligonucleotides  825  are different. In some embodiments, the antibody molecular label  825   am  of different binding reagent oligonucleotides  825  are different. 
     The binding reagent oligonucleotides  825  can be barcoded using a plurality of barcodes  815  (e.g., barcodes  815  associated with a particle, such as a bead  810 ) to create a plurality of barcoded binding reagent oligonucleotides  840 . In some embodiments, a barcode  815  can include a poly(dT) region  815   t  for binding to a binding reagent oligonucleotide  825 , optionally a molecular label  815   m  (e.g., for determining the number of occurrences of the binding reagent oligonucleotides), a cell label  815   c , and a universal label  815   u . In some embodiments the barcode  815  is hybridized to the poly(dT) region  815   t  of binding reagent oligonucleotides  825 . In some embodiments barcoded binding reagent oligonucleotides  840  are generated by extending (e.g., by reverse transcription) the barcode  815  hybridized to the binding reagent oligonucleotide  825 . In some embodiments, barcoded binding reagent oligonucleotides  840  comprise primer adapter  825   pa , an antibody molecular label  825   am  (e.g., a unique molecular label sequence), an antibody barcode  825   ab  (e.g., a unique identifier sequence), an alignment sequence  825   bb , poly(dT) region  815   t , molecular label  815   m , cell label  815   c , and universal label  815   u.    
     In some embodiments, the barcoded binding reagent oligonucleotides disclosed herein comprises two unique molecular label sequences: a molecular label sequence derived from the barcode (e.g., molecular label  815   m ) and a molecular label sequence derived from a binding reagent oligonucleotide (e.g., antibody molecular label  825   am , the first molecular label sequence of a sample indexing oligonucleotide, the second molecular label sequence of a cellular component-binding reagent specific oligonucleotide). As used herein, “dual molecular indexing” refers to methods and compositions disclosed herein employing barcoded binding reagent oligonucleotides (or products thereof) that comprise a first unique molecular label sequence and second unique molecular label sequence (or complementary sequences thereof). In some embodiments, the methods of sample identification and of quantitative analysis of cellular component targets disclosed herein can comprise obtaining the sequence of information of the barcode molecular label sequence and/or the binding reagent oligonucleotide molecular label sequence. In some embodiments, the number of barcode molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. In some embodiments, the number of binding reagent oligonucleotide molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells. In some embodiments, the number of both the binding reagent oligonucleotide molecular label sequences and barcode molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data indicates the number of copies of the at least one cellular component target in the one or more of the plurality of cells 
     The use of PCR to amplify the amount of material before starting the sequencing protocol adds the potential for artifacts, such as artifactual recombination during amplification occurs when premature termination products prime a subsequent round of synthesis). In some embodiments, the methods of dual molecular indexing provided herein allow the identification of PCR chimeras given sufficient sequencing depth. Additionally, in some embodiments, the addition of the unique molecular label sequence to the binding reagent oligonucleotide increases stochastic labelling complexity. Thus, in some embodiments, the presence of the unique molecular label sequence in the binding reagent oligonucleotide can overcome UMI diversity limitations. In some embodiments the methods of dual molecular indexing provided herein decrease the number of cellular component targets flagged as “Saturated” during post-sequencing molecular coverage calculations by at least about 2% (e.g., 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30%, 40%, 50%, 75%, 100%, 150%, 200%, 250%, 500%, 1000%, or higher and overlapping ranges therein) compared to if the methods and compositions are not used. 
     Methods and Compositions for Labeling Nucleic Acid Targets 
     There are provided, in some embodiments, optimal DNA oligonucleotide design for protein quantitation using antibody-oligonucleotides to allow separate PCR workflows for protein quantitation and RNA quantitation. There are provided DNA oligonucleotide designs for protein quantitation using antibody-oligonucleotides in AbSeq. Some embodiments provided herein enable a separate, but parallel workflow for protein quantitation and mRNA quantitation from exactly the same beads. After cDNA synthesis, the ab-oligo that can now contain a UMI and cell label can be denatured off and used in a solution-phase only PCR reaction, while the beads can be used in a separate PCR reaction for amplifying the cDNA. Some of the methods and compositions provided herein rely on the finding provided herein that a DNA oligonucleotide can be used as a primer for cDNA synthesis by the reverse transcriptase enzyme, with the resulting product able to be used as a template in downstream PCR steps that an mRNA template cannot. 
     In RNA quantitation using UMIs, the mRNA sequence is copied onto the bead that contains the cell label and the UMI. Such a workflow is employed because the oligodT sequence used to capture the mRNA is the “primer” for cDNA synthesis of the RNA template by the reverse transcriptase enzyme. Even though the polyA tail of the RNA could conceivably also be used as a primer to copy the UMI and the cell label onto the RNA, that RNA/DNA chimera would not survive in PCR since most polymerases used in PCR do not use RNA as a template. The DNA oligonucleotide used in AbSeq is a full DNA molecule that is released during cell lysis and is bound to the magnetic bead containing the cell label, UMI and oligo dT sequence. As disclosed herein, the 3′ polyA end of the AbO oligonucleotide can be used as a “primer” by the reverse transcriptase enzyme to actually copy the UMI and the cell label onto the DNA oligonucleotide sequence. The reverse transcriptase thus is now making a template that can be used in PCR, that is not covalently attached to the capture bead. In some embodiments of the methods provided herein, this template can be denatured from the bead (using heat or chemical means) and used in a PCR reaction for protein quantitation that is separate from the bead-containing PCR reaction used for mRNA quantitation.  FIG.  12    shows a non-limiting exemplary workflow of separate PCR workflows for protein quantitation and RNA quantitation. In some embodiments, the method comprises separating the antibody bound to the extended oligonucleotide (extended with the molecular index and stochastic label). In some embodiments, sensitivity is improved by practicing beadless PCR. There are further provided, in some embodiments, methods of optimizing the design of the DNA oligonucleotide (the length of the polyA tail, the use of modified bases) to ensure high fidelity copying of the UMI and cell label onto the 3′ end of the DNA oligo. 
     In some embodiments, the enzyme used for cDNA synthesis onto the bead is reverse transcriptase, which, in some embodiments, can also use DNA as a template. In some embodiments, another DNA polymerase such as Klenow exo—is added to extend the 3′ end of the oligonucleotide to be used for protein quantitation. 
     An advantage of the methods and compositions provided herein employing separate PCR workflows for mRNA and protein quantification is that the currently practiced workflow copies the mRNA sequence onto the bead that contains the cell label and UMI and the bead must therefore go into the PCR1 reaction. Magnetic beads are often inhibitory to PCR in some manner, often by adsorption of enzyme by the beads themselves. However, the approach provided herein copies the UMI and cell label onto the AbSeq oligonucleotide. Thus, after the reverse transcription step the AbSeq oligonucleotide can be denatured off of the bead and the supernatant containing the extended Ab-oligo, UMI and cell label, can go through a separate but parallel PCR workflow (without beads) to do the protein quantitation. This solution solves the problem that the mRNA molecule captured by beads cannot serve as a template for PCR after reverse transcription. As provided herein, the DNA oligonucleotide can serve as a primer for RT and subsequently as a template for PCR downstream, so it can successfully be used to add a complementary sequence copy of the UMI and cell label on to an AbSeq antibody-oligo. 
     In some embodiments of the methods and compositions provided herein, the oligonucleotide barcode comprises a cleavage region (comprising, for example, one or more cleavage sites such as a non-canonical nucleotide (e.g., deoxyuridine) or a restriction enzyme recognition sequence) as described in U.S. Provisional Patent Application Ser. No. 62/960,609, filed Jan. 13, 2020, entitled “IMPROVED CELL CAPTURE USING DU CONTAINING OLIGONUCLEOTIDES”, the content of which is incorporated herein by reference in its entirety. 
       FIG.  13 A  shows schematic illustrations of non-limiting exemplary compositions for labeling nucleic acid targets. A barcode (e.g., a stochastic barcode, an oligonucleotide barcode  1340 ) can comprise a target binding region (e.g., a poly(dT)  1312 ) that can bind to nucleic acid targets (e.g., poly-adenylated RNA transcripts or other nucleic acid targets, such as for example, antibody oligonucleotides  1342 , whether associated with antibodies or have dissociated from antibodies) via a poly(dA) tail  1318 , or other nucleic acid targets, for labeling or barcoding (e.g., unique labeling). The target-binding region can comprise a gene-specific sequence, an oligo(dT) sequence, a random multimer, or any combination thereof. The oligonucleotide barcode  1340  can also comprise a number of labels. The oligonucleotide barcode  1340  can include first molecular label (ML)  1310  and a sample label (e.g, partition label, cell label (CL)  1308 ) for labeling the transcripts and/or tracking sample origins of the RNA transcripts (or nucleic acid targets, such as for example, antibody oligonucleotides  1342 , whether associated with antibodies or have dissociated from antibodies), respectively, along with one or more additional sequences flanking the first molecular label  1310 /cell label  1308  region of each barcode  1340  for subsequent reactions, such as, for example, a first universal sequence  1306  (e.g., Read 1 sequence). The cell label  1308  can comprise a cell label1  1308   a , linker1  1308   b , cell label2  1308   c , linker2  1308   d , and/or cell label3  1308   e . The repertoire of sequences of the molecular labels in the oligonucleotide barcodes per sample can be sufficiently large for stochastic labeling of RNA transcripts. In some embodiments, the sample label is a partition label. In some embodiments, the sample label is a cell label. In some embodiments the barcode is associated with a solid support (e.g., a particle). Cellular component binding reagent specific oligonucleotide  1342  (e.g., an antibody oligonucleotide, Ab-oligo, AbSeq oligonucleotide) can comprise a second universal sequence  1322 , a molecule label (e.g., a second molecular label  1324 ) a unique identifier sequence  1326 , a sequence complementary to the target binding region (e.g., a poly(A) tail  1318 ), and/or an alignment sequence  1344 . The target specific (e.g., gene specific) reverse primers that can be employed during PCR1 amplification are also depicted in  FIG.  13 A . 
       FIG.  13 B  shows schematic illustrations of non-limiting exemplary sequences and complements attached to the bead after extension (e.g., reverse transcription) according to the methods and compositions provided herein. An extended cellular component-binding reagent specific oligonucleotide  1332  can comprise a complement of the first molecular label  1310   rc , a complement of the cell label  1308   rc , and a complement of the first universal sequence  1306   rc . A first barcoded nucleic acid molecule  1330  can comprise a complement of the unique identifier sequence  1326   rc , a complement of the second molecular label  1324   rc , and a complement of the second universal sequence  1322   rc . A second barcoded nucleic acid molecule  1304  can comprise cDNA  1316   c  (the reverse complementary sequence of RNA sequence  1316   r  of poly-adenylated transcript  1314 ). In some embodiments, cellular component binding reagent specific oligonucleotide is associated with a cellular component binding reagent (e.g., antibody  1328 ). 
       FIG.  13 C  shows schematic illustrations of non-limiting soluble material that can be denatured off after extension (e.g., reverse transcription) according to the methods and compositions provided herein. such as, for example, Ab-oligo extended in RT, or amplification product  1334 , Ab-oligo not extended in RT  1336 , and/or a complement to the bead oligonucleotide  1338  (e.g., undenatured product from bead manufacturer). 
       FIGS.  14 A- 14 C  show schematic illustrations of non-limiting exemplary workflows for labeling nucleic acid targets. A barcode (e.g., a stochastic barcode, an oligonucleotide barcode  1402 ) can comprise a target binding region (e.g., a poly(dT)  1410 ) that can bind to nucleic acid targets (e.g., poly-adenylated RNA transcripts or other nucleic acid targets, such as for example, antibody oligonucleotides  1414 , whether associated with antibodies or have dissociated from antibodies) via a poly(dA) tail  1422 , or other nucleic acid targets, for labeling or barcoding (e.g., unique labeling). The target-binding region can comprise a gene-specific sequence, an oligo(dT) sequence, a random multimer, or any combination thereof. The oligonucleotide barcode  1402  can also comprise a number of labels. The oligonucleotide barcode  1402  can include first molecular label (ML)  1408  and a sample label (e.g, partition label, cell label (CL)  1406 ) for labeling the transcripts and/or tracking sample origins of the RNA transcripts (or nucleic acid targets, such as for example, antibody oligonucleotides  1414 , whether associated with antibodies or have dissociated from antibodies), respectively, along with one or more additional sequences flanking the first molecular label  1408 /cell label  1406  region of each barcode  1402  for subsequent reactions, such as, for example, a first universal sequence  1404  (e.g., Read 1 sequence). The repertoire of sequences of the molecular labels in the oligonucleotide barcodes per sample can be sufficiently large for stochastic labeling of RNA transcripts. In some embodiments, the sample label is a partition label. In some embodiments, the sample label is a cell label. In some embodiments the barcode is associated with a solid support (e.g., a particle  1412 ). A plurality of barcodes  1402  can be associated with particle  1412 . In some embodiments, the particle is a bead. The bead can be a polymeric bead, for example a deformable bead or a gel bead, functionalized with barcodes or stochastic barcodes (such as gel beads from 10× Genomics (San Francisco, Calif.)). In some implementation, a gel bead can comprise a polymer-based gels. Gel beads can be generated, for example, by encapsulating one or more polymeric precursors into droplets. Upon exposure of the polymeric precursors to an accelerator (e.g., tetramethylethylenediamine (TEMED)), a gel bead may be generated. Cellular component binding reagent specific oligonucleotide  1414  can comprise a second universal sequence  1416 , a molecule label (e.g., a second molecular label  1418 ) a unique identifier sequence  1420 , a sequence complementary to the target binding region (e.g., a poly(A) tail  1422 ), or complements thereof. In some embodiments, cellular component binding reagent specific oligonucleotide  1414  is associated with a cellular component binding reagent (e.g., antibody  1424 ). 
     The workflow can comprise hybridization  1400   a  of the cellular component binding reagent specific oligonucleotide  1414  and oligonucleotide barcode  1402 . The workflow can comprise extending  1400   b  the cellular component-binding reagent specific oligonucleotides  1414  hybridized to the oligonucleotide barcode  1402  to generate an extended cellular component-binding reagent specific oligonucleotide  1426  comprising a complement of the first molecular label  1408   rc , a complement of the cell label  1406   rc , and a complement of the first universal sequence  1404   rc . In some embodiments, the extension reaction  1400   b  can comprise extending the oligonucleotide barcode  1402  hybridized to the cellular component binding reagent specific oligonucleotide  1414  to generate a first barcoded nucleic acid molecule  1428  comprising a complement of the unique identifier sequence  1420   rc , a complement of the second molecular label  1418   rc , and a complement of the second universal sequence  1416   rc.    
     The workflow can comprise denaturing  1400   c  (e.g., heating and/or alkaline denaturation) the extended cellular component-binding reagent specific oligonucleotide  1426  to generate denatured extended cellular component-binding reagent specific oligonucleotide  1430 . In some embodiments denaturing  1400   c  generates denatured first barcoded nucleic acid molecule  1432 . The workflow can comprise separating  1400   d  the denatured extended cellular component-binding reagent specific oligonucleotide  1430  from the particle  1412  (and/or oligonucleotide barcodes  1402 ) to generate separated extended cellular component-binding reagent specific oligonucleotide  1434 . 
     Separated extended cellular component-binding reagent specific oligonucleotide  1434  can serve as a template for one or more extension reactions (e.g., random priming and extension) and/or amplification reactions (e.g., PCR). For example, separated extended cellular component-binding reagent specific oligonucleotide  1434  can undergo a first round of amplification (“PCR1”)  1400   e  employing amplification primers  1436  and  1438  that can anneal to first universal sequence and second universal sequence (or complements thereof), respectively. PCR1  1400   e  can generate amplified separated extended cellular component-binding reagent specific oligonucleotide  1440 . PCR1  1400   e  can comprise 1-30 cycles (e.g., 15 cycles). The workflow can comprise library amplification (“Index PCR”)  1400   f . Index PCR  1400   f  can comprise library amplification of amplified separated extended cellular component-binding reagent specific oligonucleotide  1440  with sequencing library amplification primers  1442  and  1444 . Sequencing library amplification primers  1442  and  1444  can anneal to first universal sequence and second universal sequence (or complements thereof), respectively. Library PCR  1400   f  can add sequencing adapters (e.g., P5  1448  and P7  1452 ) and sample index  1450  (e.g., i5, i7) via overhangs in sequencing library amplification primers  1442  and  1444 . Library PCR amplicons  1446  can be sequenced and subjected to downstream methods of the disclosure. Sequencing  1400   f  using 150 bp×2 sequencing can reveal the cell label, the first molecular label and/or unique identifier sequence (or a partial sequence of the unique identifier sequence) on read 1, the unique identifier sequence (or a partial sequence of the unique identifier sequence) and/or the second molecular label on read 2, and the sample index on index 1 read and/or index 2 read. Library PCR  1400   f  can comprise 1-30 cycles (e.g., 15 cycles). 
       FIGS.  15 A- 15 D  show schematic illustrations of non-limiting exemplary workflows for simultaneous measurement of protein and gene expressions in cells. A barcode (e.g., a stochastic barcode, an oligonucleotide barcode  1502 ) can comprise a target binding region (e.g., a poly(dT)  1510 ) that can bind to nucleic acid targets (e.g., poly-adenylated RNA transcripts  1514  or other nucleic acid targets, such as for example, antibody oligonucleotides  1520 , whether associated with antibodies or have dissociated from antibodies) via a poly(dA) tail  1518  or  1528  or other nucleic acid targets, for labeling or barcoding (e.g., unique labeling). Poly-adenylated RNA transcripts  1514  can comprise RNA sequence  1516   r  and poly(dA) tail  1518 . The target-binding region can comprise a gene-specific sequence, an oligo(dT) sequence, a random multimer, or any combination thereof. The oligonucleotide barcode  1502  can also comprise a number of labels. The oligonucleotide barcode  1502  can include first molecular label (ML)  1508  and a sample label (e.g, partition label, cell label (CL)  1506 ) for labeling the transcripts and/or tracking sample origins of the RNA transcripts  1514  (or nucleic acid targets, such as for example, antibody oligonucleotides  1520 , whether associated with antibodies or have dissociated from antibodies), respectively, along with one or more additional sequences flanking the first molecular label  1508 /cell label  1506  region of each barcode  1502  for subsequent reactions, such as, for example, a first universal sequence  1504  (e.g., Read 1 sequence). The repertoire of sequences of the molecular labels in the oligonucleotide barcodes per sample can be sufficiently large for stochastic labeling of RNA transcripts. In some embodiments, the sample label is a partition label. In some embodiments, the sample label is a cell label. In some embodiments the barcode is associated with a solid support (e.g., a particle  1512 ). A plurality of barcodes  1502  can be associated with particle  1512 . In some embodiments, the particle is a bead. The bead can be a polymeric bead, for example a deformable bead or a gel bead, functionalized with barcodes or stochastic barcodes (such as gel beads from 10× Genomics (San Francisco, Calif.)). In some implementation, a gel bead can comprise a polymer-based gels. Gel beads can be generated, for example, by encapsulating one or more polymeric precursors into droplets. Upon exposure of the polymeric precursors to an accelerator (e.g., tetramethylethylenediamine (TEMED)), a gel bead may be generated. Cellular component binding reagent specific oligonucleotide  1520  can comprise a second universal sequence  1522 , a molecule label (e.g., a second molecular label  1524 ) a unique identifier sequence  1526 , a sequence complementary to the target binding region (e.g., a poly(A) tail  1528 ), or complements thereof. In some embodiments, cellular component binding reagent specific oligonucleotide  1520  is associated with a cellular component binding reagent (e.g., antibody  1530 ). 
     The workflow can comprise hybridization  1500   a  of the cellular component binding reagent specific oligonucleotide  1520  and oligonucleotide barcode  1502 . The workflow can comprise hybridization  1500   a  of the poly-adenylated RNA transcript  1514  and oligonucleotide barcode  1502 . The workflow can comprise extending  1500   b  the cellular component-binding reagent specific oligonucleotides  1520  hybridized to the oligonucleotide barcode  1502  to generate an extended cellular component-binding reagent specific oligonucleotide  1532  comprising a complement of the first molecular label  1508   rc , a complement of the cell label  1506   rc , and a complement of the first universal sequence  1504   rc . In some embodiments, the extension reaction  1500   b  can comprise extending the oligonucleotide barcode  1502  hybridized to the cellular component binding reagent specific oligonucleotide  1520  to generate a first barcoded nucleic acid molecule  1534  comprising a complement of the unique identifier sequence  1526   rc , a complement of the second molecular label  1524   rc , and a complement of the second universal sequence  1522   rc . In some embodiments, the extension reaction  1500   b  can comprise extending the oligonucleotide barcode  1502  hybridized to the poly-adenylated RNA transcript  1514  to generate a second barcoded nucleic acid molecule  1536  comprising cDNA  1516   c  (the reverse complementary sequence of RNA sequence  1516   r ). 
     The workflow can comprise denaturing  1500   c  (e.g., heating and/or alkaline denaturation) the extended cellular component-binding reagent specific oligonucleotide  1532  to generate denatured extended cellular component-binding reagent specific oligonucleotide  1538 . The workflow can comprise separating  1500   d  the denatured extended cellular component-binding reagent specific oligonucleotide  1538  from the particle  1512  (and/or oligonucleotide barcodes  1502  and/or first barcoded nucleic acid molecule  1534  and/or second barcoded nucleic acid molecule  1536 ) to generate separated extended cellular component-binding reagent specific oligonucleotide  1544 , first barcoded nucleic acid molecule  1542  and/or second barcoded nucleic acid molecule  1540 . 
     First barcoded nucleic acid molecule  1542  and second barcoded nucleic acid molecule  1540  can serve as a template for one or more extension reactions (e.g., random priming and extension) and/or amplification reactions (e.g., PCR) and/or sequencing reactions  1500   e . Separated extended cellular component-binding reagent specific oligonucleotide  1544  can serve as a template for one or more extension reactions (e.g., random priming and extension) and/or amplification reactions (e.g., PCR) and/or sequencing reactions  1500   f.    
     Disclosed herein include methods for labeling nucleic acid targets in a sample (e.g., intact cells, permeabilized cells, lysed cells). In some embodiments, the method comprises: contacting copies of a nucleic acid target in the sample with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target, wherein the nucleic acid target comprises DNA and is associated with a cellular component binding reagent; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     Disclosed herein include methods for labeling nucleic acid targets in a sample (e.g., intact cells, permeabilized cells, lysed cells). In some embodiments, the method comprises: contacting copies of a nucleic acid target comprising a poly(dA) sequence with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target, wherein the target-binding region comprises a poly(dT) sequence; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     Disclosed herein include methods for labeling nucleic acid targets in a sample (e.g., intact cells, permeabilized cells, lysed cells). In some embodiments, the method comprises: contacting copies of a nucleic acid target with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the nucleic acid target; extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase to generate a plurality of extended nucleic acid targets each comprising a complement of the first molecular label; and denaturing the plurality of extended nucleic acid targets hybridized to the plurality of oligonucleotide barcodes. 
     The nucleic acid target can be associated with a cellular component binding reagent. The cellular component-binding reagent can be capable of specifically binding to at least one of a plurality of cellular component targets. The method can comprise: dissociating the nucleic acid target and the cellular component binding reagent, such as before contacting the copies of a nucleic acid target with the plurality of oligonucleotide barcodes. The method can comprise separating the plurality of extended nucleic acid targets from the plurality of oligonucleotide barcodes to generate a plurality of separated extended nucleic acid targets. Separating the plurality of extended nucleic acid targets from the plurality of oligonucleotide barcodes can comprise magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. 
     The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of extended nucleic acid targets, or products thereof. The method can comprise: amplifying the plurality of extended nucleic acid targets to generate a plurality of amplified extended nucleic acid targets, wherein determining the copy number of the nucleic acid target in the sample comprises: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of amplified extended nucleic acid targets, or products thereof. The method can comprise: amplifying the plurality of separated extended nucleic acid targets to generate a plurality of amplified separated extended nucleic acid targets, wherein determining the copy number of the nucleic acid target in the sample comprises: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of amplified separated extended nucleic acid targets, or products thereof. Determining the copy number of the nucleic acid target can comprise determining the copy number of each of the plurality of nucleic acid targets in the sample based on the number of first molecular labels with distinct sequences associated with amplified extended nucleic acid targets of the plurality of amplified extended nucleic acid targets comprising a sequence of the each of the plurality of nucleic acid targets. Determining the copy number of the nucleic acid target can comprise determining the copy number of each of the plurality of nucleic acid targets in the sample based on the number of first molecular labels with distinct sequences associated with amplified separated extended nucleic acid targets of the plurality of amplified extended nucleic acid targets comprising a sequence of the each of the plurality of nucleic acid targets. The sequence of the each of the plurality of nucleic acid targets can comprise a subsequence of the each of the plurality of nucleic acid targets. The sequence of the nucleic acid target in the plurality of extended nucleic acid targets can comprise a subsequence of the nucleic acid target. 
     The method can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target in the presence of a polymerase to generate a plurality of barcoded nucleic acid molecules each comprising a sequence complementary to the at least a portion of the nucleic acid target and a first molecular label. Extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target using a reverse transcriptase and/or a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. In some embodiments, extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes can comprise extending the copies of the nucleic acid target hybridized to the plurality of oligonucleotide barcodes using reverse transcriptase and/or a DNA polymerase (e.g., a Klenow Fragment) lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. The reverse transcriptase can comprise a viral reverse transcriptase (e.g., a murine leukemia virus (MLV) reverse transcriptase and/or a Moloney murine leukemia virus (MMLV) reverse transcriptase. The step of extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target and the step of extending the plurality of oligonucleotide barcodes hybridized to the copies of the nucleic acid target are performed simultaneously. 
     The target-binding region can comprise a poly(dT) sequence and/or the nucleic acid target can comprise a poly(dA) sequence. The nucleic acid target can comprise an alignment sequence adjacent to the poly(dA) sequence. The nucleic acid target can be associated with the cellular component-binding reagent through a linker. The nucleic acid target can be configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the nucleic acid target from the cellular component-binding reagent. The plurality of extended nucleic acid targets can comprise barcoded deoxyribonucleic acid (DNA) molecules. 
     The nucleic acid target can comprise a nucleic acid molecule (e.g., ribonucleic acid (RNA), messenger RNA (mRNA), microRNA, small interfering RNA (siRNA), RNA degradation product, RNA comprising a poly(A) tail, or any combination thereof). The nucleic acid target can comprise a sample indexing oligonucleotide, and optionally the sample indexing oligonucleotide can comprise a sample indexing sequence, and sample indexing sequences of at least two sample indexing compositions of a plurality of sample indexing compositions can comprise different sequences. The nucleic acid target can comprise a cellular component-binding reagent specific oligonucleotide. A cellular component-binding reagent specific oligonucleotide can comprise a unique identifier sequence for the cellular component-binding reagent. 
     Each oligonucleotide barcode can comprise a first universal sequence. The plurality of extended nucleic acid targets can comprise a complement of the first universal sequence. Amplifying the plurality of extended nucleic acid targets and/or amplifying the plurality of separated extended nucleic acid targets can comprise using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and an amplification primer. The amplification primer can be a target-specific primer. The nucleic acid target can comprise a second universal sequence. Amplifying the plurality of extended nucleic acid targets and/or amplifying the plurality of separated extended nucleic acid targets can comprise using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof. The method can comprise: obtaining sequence information of the plurality of extended nucleic acid molecules, or products thereof. Obtaining the sequence information can comprise attaching sequencing adaptors to the plurality of extended nucleic acid targets, or products thereof. The sample can comprise a single cell, a plurality of cells (e.g., intact cells, permeabilized cells, lysed cells), a plurality of single cells, a tissue, a tumor sample, or any combination thereof. The method can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target to generate a plurality of barcoded nucleic acid molecules each comprising a sequence complementary to the at least a portion of the nucleic acid target and the first molecular label. The method can comprise obtaining sequence information of the plurality of barcoded nucleic acid molecules, or products thereof, to determine the copy number of the nucleic acid target in one or more of the plurality of cells 
     The method can comprise: contacting random primers with the plurality of barcoded nucleic acid molecules, wherein each of the random primers comprises a third universal sequence, or a complement thereof, and extending the random primers hybridized to the plurality of barcoded nucleic acid molecules to generate a plurality of extension products. The method can comprise: amplifying the plurality of extension products using primers capable of hybridizing to the first universal sequence or complements thereof, and primers capable of hybridizing the third universal sequence or complements thereof, thereby generating a first plurality of barcoded amplicons. Amplifying the plurality of extension products can comprise adding sequences of binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof, to the plurality of extension products. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the first plurality of barcoded amplicons, or products thereof. Determining the copy number of the nucleic acid target in the sample can comprise determining the number of each of the plurality of nucleic acid targets in the sample based on the number of the first molecular labels with distinct sequences associated with barcoded amplicons of the first plurality of barcoded amplicons comprising a sequence of the each of the plurality of nucleic acid targets. The sequence of the each of the plurality of nucleic acid targets can comprise a subsequence of the each of the plurality of nucleic acid targets. The sequence of the nucleic acid target in the first plurality of barcoded amplicons can comprise a subsequence of the nucleic acid target. The method can comprise: amplifying the first plurality of barcoded amplicons using primers capable of hybridizing to the first universal sequence or complements thereof, and primers capable of hybridizing the third universal sequence or complements thereof, thereby generating a second plurality of barcoded amplicons. Amplifying the first plurality of barcoded amplicons can comprise adding sequences of binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof, to the first plurality of barcoded amplicons. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the second plurality of barcoded amplicons, or products thereof. The first plurality of barcoded amplicons and/or the second plurality of barcoded amplicons can comprise whole transcriptome amplification (WTA) products. 
     In some embodiments, denaturing can comprise heating and/or alkaline denaturation. In some embodiments, the first universal sequence, the second universal sequence, and/or the third universal sequence can be the same or different. In some embodiments, the first universal sequence, the second universal sequence, and/or the third universal sequence can comprise the binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof. The sequencing adaptors can comprise a P5 sequence, a P7 sequence, complementary sequences thereof, and/or portions thereof. The sequencing primers can comprise a Read 1 sequencing primer, a Read 2 sequencing primer, complementary sequences thereof, and/or portions thereof. 
     The alignment sequence can be one or more nucleotides in length, or two or more nucleotides in length. The alignment sequence can comprise a guanine, a cytosine, a thymine, a uracil, or a combination thereof. The alignment sequence can comprise a poly(dT) sequence, a poly(dG) sequence, a poly(dC) sequence, a poly(dU) sequence, or a combination thereof. The alignment sequence can be 5′ to the poly(dA) region. The linker can comprise a carbon chain, optionally the carbon chain can comprise 2-30 carbons, and further optionally the carbon chain can comprise 12 carbons. The linker can comprise 5′ amino modifier C12 (5AmMC12), or a derivative thereof. The cellular component target can comprise a protein target. The cellular component target can comprise a carbohydrate, a lipid, a protein, an extracellular protein, a cell-surface protein, a cell marker, a B-cell receptor, a T-cell receptor, a major histocompatibility complex, a tumor antigen, a receptor, an intracellular protein, or any combination thereof. The cellular component target can be on a cell surface. 
     At least 10 of the plurality of oligonucleotide barcodes can comprise different first molecular label sequences. The plurality of oligonucleotide barcodes can be associated with a solid support. The plurality of oligonucleotide barcodes each can comprise a cell label. Each cell label of the plurality of oligonucleotide barcodes can comprise at least 6 nucleotides. Oligonucleotide barcodes associated with the same solid support can comprise the same cell label or different cell labels. The solid support can comprise a synthetic particle or a planar surface. The sample can comprise a single cell, and the method can comprise associating a synthetic particle comprising the plurality of the oligonucleotide barcodes with the single cell in the sample. The synthetic particle and the single cell can be in the same partition (e.g., a well or a droplet). At least one of the plurality of oligonucleotide barcodes can be immobilized on, partially immobilized, enclosed in, or partially enclosed in the synthetic particle. 
     The synthetic particle can be disruptable (e.g., a disruptable hydrogel particle). The synthetic particle can comprise a bead (e.g., a Sepharose bead, a streptavidin bead, an agarose bead, a magnetic bead, a conjugated bead, a protein A conjugated bead, a protein G conjugated bead, a protein A/G conjugated bead, a protein L conjugated bead, an oligo(dT) conjugated bead, a silica bead, a silica-like bead, an anti-biotin microbead, an anti-fluorochrome microbead, or any combination thereof). The synthetic particle can comprise a material selected from the group consisting of polydimethylsiloxane (PDMS), polystyrene, glass, polypropylene, agarose, gelatin, hydrogel, paramagnetic, ceramic, plastic, glass, methylstyrene, acrylic polymer, titanium, latex, Sepharose, cellulose, nylon, silicone, and any combination thereof. 
     Methods for Measuring Cellular Component Expression in Cells 
     Disclosed herein include methods for measuring cellular component expression in cells. In some embodiments, the method comprises: contacting a plurality of cellular component-binding reagents with a plurality of cells (e.g., intact cells, permeabilized cells, lysed cells) comprising a plurality of cellular component targets, wherein each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier sequence for the cellular component-binding reagent, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets; and contacting the cellular component-binding reagent specific oligonucleotides with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the cellular component-binding reagent specific oligonucleotide. The method can comprise extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended cellular component-binding reagent specific oligonucleotides each comprising a complement of the first molecular label. The method can comprise denaturing the plurality of extended cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes. The method can comprise obtaining sequence information of the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, to determine the number of copies of at least one cellular component target of the plurality of cellular component targets in one or more of the plurality of cells. In some embodiments, the plurality of cells can comprise T cells, B cells, tumor cells, myeloid cells, blood cells, normal cells, fetal cells, maternal cells, or a mixture thereof. 
     The method can comprise: prior to extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes: partitioning the plurality of cells associated with the plurality of cellular component-binding reagents to a plurality of partitions, wherein a partition of the plurality of partitions comprises a single cell from the plurality of cells associated with the cellular component-binding reagents; in the partition comprising the single cell, contacting the cellular component-binding reagent specific oligonucleotides with the plurality of oligonucleotide barcodes. The plurality of oligonucleotide barcodes are associated with a solid support, and wherein a partition of the plurality of partitions can comprise a single solid support. The method can comprise separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended cellular component-binding reagent specific oligonucleotides. Separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes can comprise magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. Partitioning the plurality of cells can comprise partitioning the plurality of cells associated with the plurality of cellular component-binding reagents and a plurality of solid supports comprising the solid support to the plurality of partitions (e.g., wells or droplets), wherein the partition of the plurality of partitions can comprise the single cell from the plurality of cells associated with the cellular component-binding reagent and the solid support. 
     Each oligonucleotide barcode can comprise a first universal sequence. The plurality of extended cellular component-binding reagent specific oligonucleotides can comprise a complement of the first universal sequence. The cellular component-binding reagent specific oligonucleotide can comprise a second universal sequence. In some embodiments, obtaining sequence information of the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, comprises: amplifying the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof, using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof, to generate a plurality of amplified extended cellular component-binding reagent specific oligonucleotides; and obtaining sequencing data of the plurality of amplified extended cellular component-binding reagent specific oligonucleotides, or products thereof. The method can comprise: after contacting the plurality of cellular component-binding reagents with the plurality of cells, removing one or more cellular component-binding reagents of the plurality of cellular component-binding reagents that are not contacted with the plurality of cells, such as removing the one or more cellular component-binding reagents not contacted with the respective at least one of the plurality of cellular component targets. 
     The cellular component-binding reagent specific oligonucleotide can comprise a second molecular label. At least ten of the plurality of cellular component-binding reagent specific oligonucleotides can comprise different second molecular label sequences. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and wherein the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are identical. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and wherein the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are different. 
     The number of unique first molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data can indicate the number of copies of the at least one cellular component target in the one or more of the plurality of cells. The number of unique second molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data can indicate the number of copies of the at least one cellular component target in the one or more of the plurality of cells. 
     Obtaining the sequence information can comprise attaching sequencing adaptors to the plurality of extended cellular component-binding reagent specific oligonucleotides, or products thereof. In some embodiments, extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes can comprise extending cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase and/or a DNA polymerase (e.g., a Klenow Fragment) lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. 
     The target-binding region can comprise a poly(dT) sequence. The cellular component-binding reagent specific oligonucleotide can comprise a poly(dA) region, optionally the cellular component-binding reagent specific oligonucleotide can comprise an alignment sequence adjacent to the poly(dA) region. The cellular component-binding reagent specific oligonucleotide can be associated with the cellular component-binding reagent through a linker. The cellular component-binding reagent specific oligonucleotide can be configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the cellular component-binding reagent specific oligonucleotide from the cellular component-binding reagent. 
     Disclosed herein include compositions (e.g., kits) for measuring cellular component expression in cells. In some embodiments, the composition comprises a plurality of cellular component-binding reagents. In some embodiments, each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier sequence for the cellular component-binding reagent. In some embodiments, cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets. The composition can comprise oligonucleotide barcodes described herein. Oligonucleotide barcodes can comprise a first molecular label and a target-binding region capable of hybridizing to the cellular component-binding reagent specific oligonucleotide. 
     Methods for Simultaneous Measurement of Protein and Gene Expressions 
     Disclosed herein include methods for simultaneous measurement of protein and gene expressions in cells. In some embodiments, the method comprises: contacting a plurality of cellular component-binding reagents with a plurality of cells (e.g., intact cells, permeabilized cells, lysed cells) comprising a plurality of cellular component targets and copies of a nucleic acid target, wherein the nucleic acid target comprises mRNA, wherein each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier for the cellular component-binding reagent and a poly(A) sequence, wherein the cellular component-binding reagent specific oligonucleotide comprises DNA, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets; partitioning the plurality of cells associated with the cellular component-binding reagents to a plurality of partitions, wherein a partition of the plurality of partitions comprises a single cell from the plurality of cells associated with the cellular component-binding reagents; and in the partition comprising the single cell, contacting a plurality of oligonucleotide barcodes with the cellular component-binding reagent specific oligonucleotides and the copies of the nucleic acid target for hybridization, wherein the oligonucleotide barcodes each comprise a poly(T) sequence, a first universal sequence, and a first molecular label. The method can comprise extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended cellular component-binding reagent specific oligonucleotides each comprising a complement of the first molecular label and a complement of the first universal sequence. The method can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target to generate a plurality of barcoded nucleic acid molecules each comprising a sequence complementary to the at least a portion of the nucleic acid target and the first molecular label. The method can comprise separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended cellular component-binding reagent specific oligonucleotides. The method can comprise obtaining sequence information of the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, to determine the number of copies of at least one cellular component target of the plurality of cellular component targets in one or more of the plurality of cells. The method can comprise obtaining sequence information of the plurality of barcoded nucleic acid molecules, or products thereof, to determine the copy number of the nucleic acid target in one or more of the plurality of cells. 
     Separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes can comprise denaturing the plurality of extended cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes. Separating the plurality of extended cellular component-binding reagent specific oligonucleotides from the plurality of oligonucleotide barcodes can comprise magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. 
     The cellular component-binding reagent specific oligonucleotide can comprise a second universal sequence. Obtaining sequence information of the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, can comprise: amplifying the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof, to generate a plurality of amplified separated extended cellular component-binding reagent specific oligonucleotides; and obtaining sequencing data of the plurality of amplified separated extended cellular component-binding reagent specific oligonucleotides, or products thereof. 
     The cellular component-binding reagent specific oligonucleotide can comprise a second molecular label. At least ten of the plurality of cellular component-binding reagent specific oligonucleotides can comprise different second molecular label sequences. In some embodiments, the second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides are different, and the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides are identical. The second molecular label sequences of at least two cellular component-binding reagent specific oligonucleotides can be different and the unique identifier sequences of the at least two cellular component-binding reagent specific oligonucleotides can be different. The number of unique first molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data can indicate the number of copies of the at least one cellular component target in the one or more of the plurality of cells. The number of unique second molecular label sequences associated with the unique identifier sequence for the cellular component-binding reagent capable of specifically binding to the at least one cellular component target in the sequencing data can indicate the number of copies of the at least one cellular component target in the one or more of the plurality of cells. Obtaining the sequence information can comprise attaching sequencing adaptors to the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, and/or the plurality of barcoded nucleic acid molecules, or products thereof. Determining the copy number of the nucleic acid target in one or more of the plurality of cells can comprise determining the copy number of the nucleic acid target in the plurality of cells based on the number of first molecular labels with distinct sequences, complements thereof, or a combination thereof, associated with the plurality of barcoded nucleic acid molecules, or products thereof. 
     The method can comprise: contacting random primers with the plurality of barcoded nucleic acid molecules, wherein each of the random primers comprises a third universal sequence, or a complement thereof, and extending the random primers hybridized to the plurality of barcoded nucleic acid molecules to generate a plurality of extension products. The method can comprise: amplifying the plurality of extension products using primers capable of hybridizing to the first universal sequence or complements thereof, and primers capable of hybridizing the third universal sequence or complements thereof, thereby generating a first plurality of barcoded amplicons. Amplifying the plurality of extension products can comprise adding sequences of binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof, to the plurality of extension products. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the first plurality of barcoded amplicons, or products thereof. Determining the copy number of the nucleic acid target in the sample can comprise determining the number of each of the plurality of nucleic acid targets in the sample based on the number of the first molecular labels with distinct sequences associated with barcoded amplicons of the first plurality of barcoded amplicons comprising a sequence of the each of the plurality of nucleic acid targets. The sequence of the each of the plurality of nucleic acid targets can comprise a subsequence of the each of the plurality of nucleic acid targets. The sequence of the nucleic acid target in the first plurality of barcoded amplicons can comprise a subsequence of the nucleic acid target. The method can comprise: amplifying the first plurality of barcoded amplicons using primers capable of hybridizing to the first universal sequence or complements thereof, and primers capable of hybridizing the third universal sequence or complements thereof, thereby generating a second plurality of barcoded amplicons. Amplifying the first plurality of barcoded amplicons can comprise adding sequences of binding sites of sequencing primers and/or sequencing adaptors, complementary sequences thereof, and/or portions thereof, to the first plurality of barcoded amplicons. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the second plurality of barcoded amplicons, or products thereof. The first plurality of barcoded amplicons and/or the second plurality of barcoded amplicons can comprise whole transcriptome amplification (WTA) products. 
     The method can comprise: synthesizing a third plurality of barcoded amplicons using the plurality of barcoded nucleic acid molecules as templates to generate a third plurality of barcoded amplicons. Synthesizing a third plurality of barcoded amplicons can comprise performing polymerase chain reaction (PCR) amplification of the plurality of the barcoded nucleic acid molecules. Synthesizing a third plurality of barcoded amplicons can comprise PCR amplification using primers capable of hybridizing to the first universal sequence, or a complement thereof, and a target-specific primer. The method can comprise: obtaining sequence information of the third plurality of barcoded amplicons, or products thereof. Obtaining the sequence information can comprise attaching sequencing adaptors to the third plurality of barcoded amplicons, or products thereof. The method can comprise: determining the copy number of the nucleic acid target in the sample based on the number of first molecular labels with distinct sequences associated with the third plurality of barcoded amplicons, or products thereof. In some embodiments, (i) amplifying the plurality of separated extended cellular component-binding reagent specific oligonucleotides, or products thereof, (ii) extending the random primers hybridized to the plurality of barcoded nucleic acid molecules to generate a plurality of extension products and/or (iii) synthesizing a third plurality of barcoded amplicons are performed separately. 
     Extending the random primers hybridized to the plurality of barcoded nucleic acid molecules can comprise extending the random primers hybridized to the plurality of barcoded nucleic acid molecules using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. Extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes can comprise extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. Extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target using a DNA polymerase lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. The DNA polymerase can comprise a Klenow Fragment. Extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes can comprise extending the cellular component-binding reagent specific oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase. Extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target can comprise extending the plurality of oligonucleotide barcodes hybridized to the copies of a nucleic acid target using a reverse transcriptase. The reverse transcriptase can comprise a viral reverse transcriptase (e.g., murine leukemia virus (MLV) reverse transcriptase and/or a Moloney murine leukemia virus (MMLV) reverse transcriptase). 
     The cellular component-binding reagent specific oligonucleotide can comprise an alignment sequence adjacent to the poly(dA) sequence. The cellular component-binding reagent specific oligonucleotide can be associated with the cellular component-binding reagent through a linker. The cellular component-binding reagent specific oligonucleotide can be configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the cellular component-binding reagent specific oligonucleotide from the cellular component-binding reagent, optionally dissociating the cellular component-binding reagent specific oligonucleotide and the cellular component binding reagent before contacting a plurality of oligonucleotide barcodes with the cellular component-binding reagent specific oligonucleotides. The plurality of oligonucleotide barcodes can be associated with a solid support. A partition of the plurality of partitions can comprise a single solid support. Partitioning the plurality of cells can comprise partitioning the plurality of cells associated with the plurality of cellular component-binding reagents and a plurality of solid supports comprising the solid support to the plurality of partitions. A partition (e.g., a well or a droplet) of the plurality of partitions can comprise the single cell from the plurality of cells associated with the cellular component-binding reagent and the solid support. The method can comprise: after contacting the plurality of cellular component-binding reagents with the plurality of cells, removing one or more cellular component-binding reagents of the plurality of cellular component-binding reagents that are not contacted with the plurality of cells. Removing the one or more cellular component-binding reagents not contacted with the plurality of cells can comprise removing the one or more cellular component-binding reagents not contacted with the respective at least one of the plurality of cellular component targets. The plurality of cells can comprise T cells, B cells, tumor cells, myeloid cells, blood cells, normal cells, fetal cells, maternal cells, or a mixture thereof. 
     Disclosed herein include compositions (e.g., kits) for simultaneous measurement of protein and gene expressions in cells. In some embodiments, the composition comprises: a plurality of cellular component-binding reagents. In some embodiments, each of the plurality of cellular component-binding reagents comprises a cellular component-binding reagent specific oligonucleotide comprising a unique identifier for the cellular component-binding reagent and a poly(A) sequence, wherein the cellular component-binding reagent specific oligonucleotide comprises DNA, and wherein the cellular component-binding reagent is capable of specifically binding to at least one of the plurality of cellular component targets. The composition can comprise a plurality of oligonucleotide barcodes provided herein. 
     Methods for Sample Identification 
     Disclosed herein include methods for sample identification. In some embodiments, the method comprises: contacting each of a plurality of samples with a sample indexing composition of a plurality of sample indexing compositions, respectively, wherein each of the plurality of samples comprises one or more cells each comprising one or more cellular component targets, wherein the sample indexing composition comprises a cellular component-binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component-binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences. The method can comprise contacting the sample indexing oligonucleotides of the plurality of sample indexing compositions with a plurality of oligonucleotide barcodes, wherein each oligonucleotide barcode comprises a first molecular label and a target-binding region capable of hybridizing to the sample indexing oligonucleotide. The method can comprise extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes to generate a plurality of extended sample indexing oligonucleotides each comprising a complement of the first molecular label. The method can comprise denaturing the plurality of extended sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes. The method can comprise obtaining sequencing data of the plurality of extended sample indexing oligonucleotides, or products thereof. The method can comprise identifying the sample origin of at least one cell of the plurality of cells based on the sample indexing sequence of at least one extended sample indexing oligonucleotide, or product thereof, of the plurality of extended sample indexing oligonucleotides, or products thereof, in the sequencing data. 
     The method can comprise separating the plurality of extended sample indexing oligonucleotides from the plurality of oligonucleotide barcodes to generate a plurality of separated extended sample indexing oligonucleotides. Separating the plurality of extended sample indexing oligonucleotides from the plurality of oligonucleotide barcodes can comprise magnetic removal, centrifugation, filtration, chromatography, precipitation, or any combination thereof. Each oligonucleotide barcode can comprise a first universal sequence. The plurality of extended sample indexing oligonucleotides can comprise a complement of the first universal sequence. The sample indexing oligonucleotide can comprise a second molecular label. In some embodiments, the second molecular label sequences of at least two sample indexing oligonucleotides are different, and wherein the sample indexing sequences of the at least two sample indexing oligonucleotides are identical. In some embodiments, the second molecular label sequences of at least two sample indexing oligonucleotides are different, and wherein the sample indexing sequences of the at least two sample indexing oligonucleotides are different. Sample indexing sequences of at least 10, 100, or 1000 sample indexing compositions of the plurality of sample indexing compositions can comprise different sequences. The sample indexing oligonucleotide can comprise a second universal sequence. 
     Identifying the sample origin of the at least one cell can comprise identifying the presence or absence of the sample indexing sequence of at least one extended sample indexing oligonucleotide, or product thereof, in the sequencing data. In some embodiments, identifying the presence or absence of the sample indexing sequence comprises: amplifying the at least one extended sample indexing oligonucleotides, or products thereof, using a primer capable of hybridizing to the first universal sequence, or a complement thereof, and a primer capable of hybridizing to the second universal sequence, or a complement thereof, to generate a plurality of amplified extended sample indexing oligonucleotides; obtaining sequencing data of the plurality of amplified extended sample indexing oligonucleotides, or products thereof, and identifying the sample origin of the cell based on the sample indexing sequence of an amplified extended sample indexing oligonucleotide, or product thereof, of the plurality of amplified extended sample indexing oligonucleotides, or products thereof, that correspond to the at least one extended sample indexing oligonucleotide, or product thereof, in the sequencing data. Amplifying the at least one extended sample indexing oligonucleotides, or products thereof, can comprise attaching sequencing adaptors to the plurality of extended sample indexing oligonucleotides, or products thereof. In some embodiments, extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes can comprise extending sample indexing oligonucleotides hybridized to the plurality of oligonucleotide barcodes using a reverse transcriptase and/or a DNA polymerase (e.g., a Klenow Fragment) lacking at least one of 5′ to 3′ exonuclease activity and 3′ to 5′ exonuclease activity. 
     The method can comprise: removing unbound sample indexing compositions of the plurality of sample indexing compositions. Removing the unbound sample indexing compositions can comprise washing the one or more cells from each of the plurality of samples with a washing buffer. Removing the unbound sample indexing compositions can comprise selecting cells bound to at least one cellular component-binding reagent using flow cytometry. The sample indexing oligonucleotide can be configured to be detachable from the cellular component-binding reagent. The method can comprise: dissociating the sample indexing oligonucleotide from the cellular component-binding reagent. In The target-binding region can comprise a poly(dT) sequence. The sample indexing oligonucleotide can comprise a poly(dA) region. The sample indexing oligonucleotide can comprise an alignment sequence adjacent to the poly(dA) region. The sample indexing oligonucleotide can be associated with the cellular component-binding reagent through a linker. A sample of the plurality of samples can comprise a plurality of cells, a plurality of single cells, a tissue, a tumor sample, or any combination thereof. 
     Disclosed herein include compositions (e.g., kits) for sample identification. In some embodiments, the composition comprises a plurality of sample indexing compositions. In some embodiments, the sample indexing composition comprises a cellular component-binding reagent associated with a sample indexing oligonucleotide, wherein the cellular component-binding reagent is capable of specifically binding to at least one of the one or more cellular component targets, wherein the sample indexing oligonucleotide comprises a sample indexing sequence, and wherein sample indexing sequences of at least two sample indexing compositions of the plurality of sample indexing compositions comprise different sequences. The composition can comprise a plurality of oligonucleotide barcodes provided herein. 
     EXAMPLES 
     Some aspects of the embodiments discussed above are disclosed in further detail in the following examples, which are not in any way intended to limit the scope of the present disclosure. 
     Example 1 
     Oligonucleotides for Associating with Protein Binding Reagents 
     This example demonstrates designing of oligonucleotides that can be conjugated with protein binding reagents. The oligonucleotides can be used to determine protein expression and gene expression simultaneously. The oligonucleotides can also be used for sample indexing to determine cells of the same or different samples. 
     95mer Oligonucleotide Design 
     The following method was used to generate candidate oligonucleotide sequences and corresponding primer sequences for simultaneous determination of protein expression and gene expression or sample indexing. 
     1. Sequence Generation and Elimination 
     The following process was used to generate candidate oligonucleotide sequences for simultaneous determination of protein expression and gene expression or sample indexing. 
     Step 1a. Randomly generate a number of candidate sequences (50000 sequences) with the desired length (45 bps). 
     Step 1b. Append the transcriptional regulator LSRR sequence to the 5′ end of the sequences generated and a poly(A) sequence (25 bps) to the 3′ end of the sequences generated. 
     Step 1c. Remove sequences generated and appended that do not have GC contents in the range of 40% to 50%. 
     Step 1d. Remove remaining sequences with one or more hairpin structures each. 
     The number of remaining candidate oligonucleotide sequences was 423. 
     2. Primer Design 
     The following method was used to design primers for the remaining 423 candidate oligonucleotide sequences. 
     2.1 N1 Primer: Use the universal N1 sequence: 5′-GTTGTCAAGATGCTACCGTTCAGAG-3′ (LSRR sequence; SEQ ID NO. 3) as the N1 primer. 
     2.2 N2 Primer (for amplifying specific sample index oligonucleotides; e.g., N2 primer in  FIGS.  9 B- 9 D ): 
     2.2a. Remove candidate N2 primers that do not start downstream of the N1 sequence. 
     2.2b. Remove candidate N2 primers that overlap in the last 35 bps of the candidate oligonucleotide sequence. 
     2.2c. Remove the primer candidates that are aligned to the transcriptome of the species of cells being studied using the oligonucleotides (e.g., the human transcriptome or the mousetranscriptome). 
     2.2d. Use the ILR2 sequence as the default control (ACACGACGCTCTTCCGATCT; SEQ ID NO. 4) to minimize or avoid primer-primer interactions. 
     Of the 423 candidate oligonucleotide sequences, N2 primers for 390 candidates were designed. 
     3. Filtering 
     The following process was used to filter the remaining 390 candidate primer sequences. 
     3a. Eliminate any candidate oligonucleotide sequence with a random sequence ending in As (i.e., the effective length of the poly(A) sequence is greater than 25 bps) to keep poly(A) tail the same length for all barcodes. 
     3b. Eliminate any candidate oligonucleotide sequences with 4 or more consecutive Gs (&gt;3Gs) because of extra cost and potentially lower yield in oligo synthesis of runs of Gs. 
       FIG.  9 A  shows a non-limiting exemplary candidate oligonucleotide sequence generated using the method above. 
     200mer Oligonucleotide Design 
     The following method was used to generate candidate oligonucleotide sequences and corresponding primer sequences for simultaneous determination of protein expression and gene expression and sample indexing. 
     1. Sequence Generation and Elimination 
     The following was used to generate candidate oligonucleotide sequences for simultaneous determination of protein expression and gene expression and sample indexing. 
     1a. Randomly generate a number of candidate sequences (100000 sequences) with the desired length (128 bps). 
     1b. Append the transcriptional regulator LSRR sequence and an additional anchor sequence that is non-human, non-mouse to the 5′ end of the sequences generated and a poly(A) sequence (25 bps) to the 3′ end of the sequences generated. 
     1c. Remove sequences generated and appended that do not have GC contents in the range of 40% to 50%. 
     1d. Sort remaining candidate oligonucleotide sequences based on hairpin structure scores. 
     1e. Select 1000 remaining candidate oligonucleotide sequences with the lowest hairpin scores. 
     2. Primer Design 
     The following method was used to design primers for 400 candidate oligonucleotide sequences with the lowest hairpin scores. 
     2.1 N1 Primer: Use the universal N1 sequence: 5′-GTTGTCAAGATGCTACCGTTCAGAG-3′ (LSRR sequence; SEQ ID NO. 3) as the N1 primer. 
     2.2 N2 Primer (for amplifying specific sample index oligonucleotides; e.g., N2 primer in  FIGS.  9 B and  9 C ): 
     2.2a. Remove candidate N2 primers that do not start 23 nts downstream of the N1 sequence (The anchor sequence was universal across all candidate oligonucleotide sequences). 
     2.2b. Remove candidate N2 primers that overlap in the last 100 bps of the target sequence. The resulting primer candidates can be between the 48th nucleotide and 100th nucleotide of the target sequence. 
     2.2c. Remove the primer candidates that are aligned to the transcriptome of the species of cells being studied using the oligonucleotides (e.g., the human transcriptome or the mouse transcriptome). 
     2.2d. Use the ILR2 sequence, 5′-ACACGACGCTCTTCCGATCT-3′ (SEQ ID NO. 4) as the default control to minimize or avoid primer-primer interactions. 
     2.2e. Remove N2 primer candidates that overlap in the last 100 bps of the target sequence. 
     Of the 400 candidate oligonucleotide sequences, N2 primers for 392 candidates were designed. 
     3. Filtering 
     The following was used to filter the remaining 392 candidate primer sequences. 
     3a. Eliminate any candidate oligonucleotide sequence with a random sequence ending in As (i.e., the effective length of the poly(A) sequence is greater than 25 bps) to keep poly(A) tail the same length for all barcodes. 
     3b. Eliminate any candidate oligonucleotide sequences with 4 or more consecutive Gs (&gt;3Gs) because of extra cost and potentially lower yield in oligo synthesis of runs of Gs. 
       FIG.  9 B  shows a non-limiting exemplary candidate oligonucleotide sequence generated using the method above. The nested N2 primer shown in  FIG.  9 B  can bind to the antibody or sample specific sequence for targeted amplification.  FIG.  9 C  shows the same non-limiting exemplary candidate oligonucleotide sequence with a nested universal N2 primer that corresponds to the anchor sequence for targeted amplification.  FIG.  9 D  shows the same non-limiting exemplary candidate oligonucleotide sequence with a N2 primer for one step targeted amplification. 
     Altogether, these data indicate that oligonucleotide sequences of different lengths can be designed for simultaneous determination of protein expression and gene expression or sample indexing. The oligonucleotide sequences can include a universal primer sequence, an antibody specific oligonucleotide sequence or a sample indexing sequence, and a poly(A) sequence. 
     Example 2 
     Oligonucleotide-Associated Antibody Workflow 
     This example demonstrates a workflow of using an oligonucleotide-conjugated antibody for determining the expression profile of a protein target. 
     Frozen cells (e.g., frozen peripheral blood mononuclear cells (PBMCs)) of a subject are thawed. The thawed cells are stained with an oligonucleotide-conjugated antibody (e.g., an anti-CD4 antibody at 0.06 μg/100 μl (1:333 dilution of an oligonucleotide-conjugated antibody stock)) at a temperature for a duration (e.g., room temperature for 20 minutes). The oligonucleotide-conjugated antibody is conjugated with 1, 2, or 3 oligonucleotides (“antibody oligonucleotides”). The sequence of the antibody oligonucleotide is shown in  FIG.  10   . The cells are washed to remove unbound oligonucleotide-conjugated antibody. The cells are optionally stained with Calcein AM (BD (Franklin Lake, N.J.)) and Draq7™ (Abcam (Cambridge, United Kingdom)) for sorting with flow cytometry to obtain cells of interest (e.g., live cells). The cells are optionally washed to remove excess Calcein AM and Draq7™. Single cells stained with Calcein AM (live cells) and not Draq7™ (cells that are not dead or permeabilized) are sorted, using flow cytometry, into a BD Rhapsody™ cartridge. 
     Of the wells containing a single cell and a bead, the single cells in the wells (e.g., 3500 live cells) are lysed in a lysis buffer (e.g., a lysis buffer with 5 mM DTT). The mRNA expression profile of a target (e.g., CD4) is determined using BD Rhapsody™ beads. The protein expression profile of a target (e.g., CD4) is determined using BD Rhapsody™ beads and the antibody oligonucleotides. Briefly, the mRNA molecules are released after cell lysis. The Rhapsody™ beads are associated with barcodes (e.g., stochastic barcodes) each containing a molecular label, a cell label, and an oligo(dT) region. The poly(A) regions of the mRNA molecules released from the lysed cells hybridize to the poly(T) regions of the stochastic barcodes. The poly(dA) regions of the antibody oligonucleotides hybridize to the oligo(dT) regions of the barcodes. The mRNA molecules were reverse transcribed using the barcodes. The antibody oligonucleotides are replicated using the barcodes. The reverse transcription and replication optionally occur in one sample aliquot at the same time. 
     The reverse transcribed products and replicated products are PCR amplified using primers for determining mRNA expression profiles of genes of interest, using N1 primers, and the protein expression profile of a target, using the antibody oligonucleotide N1 primer. For example, the reverse transcribe products and replicated products can be PCR amplified for 15 cycles at 60 degrees annealing temperature using primers for determining the mRNA expression profiles of 488 blood panel genes, using blood panel N1 primers, and the expression profile of CD4 protein, using the antibody oligonucleotide N1 primer (“PCR 1”). Excess barcodes are optionally removed with Ampure cleanup. The products from PCR 1 are optionally divided into two aliquots, one aliquot for determining the mRNA expression profiles of the genes of interest, using the N2 primers for the genes of interest, and one aliquot for determining the protein expression profile of the target of interest, using the antibody oligonucleotide N2 primer (“PCR 2”). Both aliquots are PCR amplified (e.g., for 15 cycles at 60 degrees annealing temperature). The protein expression of the target in the cells are determined based on the antibody oligonucleotides as illustrated in  FIG.  10    (“PCR 2”). Sequencing data is obtained and analyzed after sequencing adaptor addition (“PCR 3”), such as sequencing adaptor ligation. Cell types are determined based on the mRNA expression profiles of the genes of interest. 
     Altogether, this example describes using an oligonucleotide-Conjugated antibody for determining the protein expression profile of a target of interest. This example further describes that the protein expression profile of the target of interest and the mRNA expression profiles of genes of interest can be determine simultaneously. 
     Example 3 
     Cellular Component-Binding Reagent Oligonucleotides 
       FIGS.  11 A- 11 B  show non-limiting exemplary designs of oligonucleotides for determining protein expression and gene expression simultaneously and for sample indexing.  FIG.  11 A  shows a non-limiting exemplary cellular component-binding reagent oligonucleotide (SEQ ID NO: 7) comprising a 5′ amino modifier C6 (5AmMC6) linker for antibody conjugation (e.g., can be modified prior to antibody conjugation), a universal PCR handle, an antibody-specific barcode sequence, and a poly(A) tail. While this embodiment depicts a poly(A) tail that is 25 nucleotides long, the length of the poly(A) tail can vary. In some embodiments, the antibody-specific barcode sequence is antibody clone-specific barcode for use in methods of protein expression profiling. In some embodiments, the antibody-specific barcode sequence is a sample tag sequence for use in methods of sample indexing. Exemplary design characteristics of the antibody-specific barcode sequence are, in some embodiments, a Hamming distance greater than 3, a GC content in the range of 40% to 60%, and an absence of predicted secondary structures (e.g., hairpin). In some embodiments, the universal PCR handle is employed for targeted PCR amplification during library preparation that attaches Illumina sequencing adapters to the amplicons. In some embodiments, high quality sequencing reads can be achieved by reducing sequencing diversity. 
       FIG.  11 B  shows a non-limiting exemplary cellular component-binding reagent oligonucleotide (SEQ ID NO: 8) comprising a 5′ amino modifier C12 (5AmMC12) linker for antibody conjugation, a primer adapter (e.g., a partial adapter for Illumina P7), an antibody unique molecular identifier (UMI), an antibody-specific barcode sequence, an alignment sequence, and a poly(A) tail. While this embodiment depicts a poly(A) tail that is 25 nucleotides long, the length of the poly(A) tail can range, in some embodiments, from 18-30 nucleotides. Exemplary design characteristics of the antibody-specific barcode sequence (wherein “X” indicates any nucleotide), in addition to those described in  FIG.  11 A , include, in some embodiments, an absence of homopolymers and an absence of sequences predicted in silico to bind human transcripts, mouse transcripts, Rhapsody system primers, and/or SCMK system primers. In some embodiments, the alignment sequence comprises the sequence BB (in which B is C, G, or T). Alignment sequences 1 nucleotide in length and more than 2 nucleotides in length are provided in some embodiments. The 5AmMC12 linker, can, in some embodiments, achieve a higher efficiency (e.g., for antibody conjugation or the modification prior to antibody conjugation) as compared to a shorter linker (e.g., 5AmMC6). The antibody UMI sequence can comprise “VN” and/or “NV” doublets (in which each “V” is any of A, C, or G, and in which “N” is any of A, G, C, or T), which, in some embodiments, improve informatics analysis by serving as a geomarker and/or reduce the incidence of homopolymers. In some embodiments, the presence of a unique molecular labeling sequence on the binding reagent oligonucleotide increases stochastic labelling complexity. In some embodiments, the primer adapter comprises the sequence of a first universal primer, a complimentary sequence thereof, a partial sequence thereof, or a combination thereof. In some embodiments, the primer adapter eliminates the need for a PCR amplification step for attachment of Illumina sequencing adapters that would typically be required before sequencing. In some embodiments, the primer adapter sequence (or a subsequence thereof) is not part of the sequencing readout of a sequencing template comprising a primer adapter sequence and therefore does not affect read quality of a template comprising a primer adapter. 
     Example 4 
     mRNA Whole Transcriptome Analysis (WTA) and AbSeq Library Preparation Protocol 
     This example provides an non-limiting exemplary protocol employed for creating single cell whole transcriptome mRNA and AbSeq libraries after cell capture on the BD Rhapsody™ Single-Cell Analysis System or the BD Rhapsody™ Express Single-Cell Analysis System for sequencing on Illumina sequencers. For complete instrument procedures and safety information, see the BD Rhapsody™ Single-Cell Analysis System Instrument User Guide (Doc ID 214062) or the BD Rhapsody™ Express Single-Cell Analysis System Instrument User Guide (Doc ID 214063). 
     The cDNA of mRNA targets can be first encoded on BD Rhapsody™ Cell Capture Beads as described in the instrument user guides. At the same time, the barcode information from BD Rhapsody Cell Capture Beads can also added to AbOligos during reverse transcription, which enables amplification of AbOligos in solution. To generate the AbSeq sequencing libraries, the extended AbOligos can be first denatured from the BD Rhapsody Cell Capture Beads, which are later amplified through a series of PCR steps. Meanwhile, the whole transcriptome amplification library is generated directly from the BD Rhapsody Cell Capture Beads using a random priming approach, followed by an index PCR step. Both the whole transcriptome mRNA and AbSeq libraries can be combined together for sequencing on various Illumina sequencers. 
     The protocol can be employed to screen RNA expression of single cells using a 3′ whole transcriptome analysis (WTA) approach through the BD Rhapsody™ WTA Amplification Kit for samples that have been labeled using BD® AbSeq. The data set generated from this protocol can be used to generate a custom panel for subsequent 3′ targeted mRNA sequencing. Specifically, the protocol outlines how to generate whole transcriptome libraries for BD Rhapsody Cell Capture Beads inputs between 1,000 to 10,000 resting PBMCs per sample for library generation. For BD Rhapsody Cell Capture Beads inputs between 1,000 to &lt;5,000 cells per sample, there are additional sections in the protocol (e.g., Purifying RPE product and Purification of the WTA Index PCR product (dual-sided cleanup)). In some embodiments, the protocol is useful for resting cell types other than resting PBMCs and can require protocol optimization in some embodiments.  FIGS.  16 - 17    provide non-limiting exemplary workflows for the methods provided herein. 
     Materials 
     Exonuclease I-treated beads containing sample and BD Rhapsody WTA Amplification Kit (Cat. No. 633801), depicted in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 BD RHAPSODY WTA AMPLIFICATION KIT 
               
            
           
           
               
               
               
            
               
                   
                 Component 
                 Part number 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 Nuclease-free water 
                 650000076 
               
               
                   
                 WTA Extension Buffer 
                 91-1114 
               
               
                   
                 WTA Extension Primers 
                 91-1115 
               
               
                   
                 10 mM dNTP 
                 650000077 
               
               
                   
                 Bead RT/PCR Enhancer 
                 91-1082 
               
               
                   
                 WTA Extension Enzyme 
                 91-1117 
               
               
                   
                 PCR MasterMix 
                 91-1118 
               
               
                   
                 Universal Oligo 
                 650000074 
               
               
                   
                 BD ™ AbSeq Primer 
                 91-1086 
               
               
                   
                 WTA Amplification Primer 
                 91-1116 
               
               
                   
                 Elution Buffer 
                 91-1084 
               
               
                   
                 Bead Resuspension Buffer 
                 650000066 
               
               
                   
                 Library Forward Primer 
                 91-1085 
               
               
                   
                 Library Reverse Primer 1 
                 650000080 
               
               
                   
                 Library Reverse Primer 2 
                 650000091 
               
               
                   
                 Library Reverse Primer 3 
                 650000092 
               
               
                   
                 Library Reverse Primer 4 
                 650000093 
               
               
                   
                 Sample Tag PCR1 Primer 
                 91-1088 
               
               
                   
                 Sample Tag PCR2 Primer 
                 91-1089 
               
               
                   
                   
               
            
           
         
       
     
     Additional materials include: Agencourt® AMPure® XP magnetic beads (Beckman Coulter Life Sciences, Cat. No. A63880); Absolute ethyl alcohol, molecular biology grade (major supplier); and nuclease-free water (major supplier); 6-Tube Magnetic Separation Rack for 1.5-mL tubes (New England Biolabs, Cat. No. S1506S); Qubit™ dsDNA HS Assay Kit (Thermo Fisher Scientific, Cat. No. Q32851); Agilent® DNA High Sensitivity Kit (Agilent Technologies, Cat. No. 5067-4626) OR Agilent® High Sensitivity D5000 ScreenTape (Agilent Technologies, Cat. No. 5067-5592); Agilent® High Sensitivity D5000 Reagents (Agilent Technologies, Cat. No. 5067-5593) OR Agilent® High Sensitivity D1000 ScreenTape (Agilent Technologies, Cat. No. 5067-5584) Agilent® High Sensitivity D1000 Reagents (Agilent Technologies, Cat. No. 5067-5585). 
     Initial Steps 
     Exonuclease I-treated and inactivated BD Rhapsody Cell Capture Beads were obtained. Cell Capture Beads were used within 48 hours of performing Exonuclease I treatment. Reagents in the BD Rhapsody WTA Amplification Kit were thawed at room temperature (15° C. to 25° C.), then immediately placed on ice. In some embodiments, low-retention filtered pipette tips were used. In some embodiments, when working with Cell Capture Beads, low-retention filtered tips and LoBind Tubes were used. In some embodiments, the beads pipet-mixed only and not vortexed. In some embodiments, the AMPure XP magnetic beads were brought to room temperature before use. In some embodiments the supernatants were removed without disturbing AMPure XP magnetic beads. 
     Performing Random Priming and Extension (RPE) on BD Rhapsody Cell Capture Beads with cDNA 
     Random priming products were generated as described herein. First, AbOligos with barcode information from BD Rhapsody Cell Capture Beads were denatured off of the beads and saved for AbSeq amplification. Then, random primers were hybridized to the cDNA on the BD Rhapsody Cell Capture Beads, followed by extension with an enzyme. The procedure was performed in a pre-amplification workspace. 
     1. A heat block was set to 95° C., one thermomixer was set to 37° C., and one thermomixer was set to 25° C. 
     2. In a new 1.5-mL LoBind tube, the reagents depicted in Table 2 were pipetted: 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 RANDOM PRIMER MIX 
               
            
           
           
               
               
               
               
            
               
                   
                 For 1 
                 For 1 library 
                 For 2 libraries 
               
               
                   
                 Library 
                 with 20% 
                 with 10% 
               
               
                 Kit Component 
                 (μL) 
                 overage (μL) 
                 overage (μL) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 WTA Extension Buffer 
                 20 
                 24 
                 44 
               
               
                 (Cat. No. 91-1114) 
                   
                   
                   
               
               
                 WTA Extension Primers 
                 20 
                 24 
                 44 
               
               
                 (Cat. No. 91-1115) 
                   
                   
                   
               
               
                 Nuclease-free water 
                 134 
                 160.8 
                 294.8 
               
               
                 (Cat. No. 650000076) 
                   
                   
                   
               
               
                 Total 
                 174 
                 208.8 
                 382.8 
               
               
                   
               
            
           
         
       
     
     3. The Random Primer Mix was pipet-mixed and kept at room temperature. 
     4. The tube of Exonuclease I-treated beads in Bead Resuspension buffer was placed on the 1.5-mL magnet for &lt;2 minutes. The supernatant was removed. 
     5. The tube was removed from the magnet and the beads were resuspended in 80 μL of Elution Buffer. Pipet-mixing 10 times was performed to resuspend the beads. 
     6. The tube was placed with beads in a 95° C. heat block for 5 minutes (no shaking). 
     7. A new 1.5-mL tube was labeled as AbSeq supernatant products. 
     8. The tube was briefly centrifuged, then the tube was immediately placed on a 1.5-mL magnet for &lt;2 minutes. The supernatant was removed and transferred to the AbSeq supernatant products tube. To minimize AbSeq contamination in the WTA library, the user ensured that all liquid was removed from the tube. The supernatant tube was kept at 4° C. for up to 24 hours until ready to proceed to Performing AbSeq PCR1 below. Unless adding an additional wash step below, the user proceeded immediately to step 9 to avoid drying out the beads. 
     If AbSeq product was still observed in the WTA product, an additional wash was performed at this step in some embodiments. Adding this wash can help minimize the appearance of that peak. If adding this wash, steps a and b below were conducted. Otherwise, the user proceeded immediately to step 9 to avoid drying out the beads. 
     Optional Additional Wash: 
     a. The tube with the BD Rhapsody Cell Capture beads was removed from the magnet, and a low-retention tip was used to pipet 80 μL of nuclease-free water into the tube. Pipet-mixing 10 times was performed to resuspend the beads. 
     b. After briefly centrifuging the tube, the tube was placed on a 1.5-mL magnet for &lt;2 minutes. The user removed and disposed of the supernatant and proceeded to step 9. 
     9. The tube with the BD Rhapsody Cell Capture beads was removed from the magnet, and a low-retention tip was used to pipet 174 μL of Random Primer Mix into the tube. Pipet-mixing 10 times was performed to resuspend the beads. 
     10. The tube was incubated in the following order:
         a. 950 in a heat block (no shaking) for 5 minutes   b. Thermomixer at 1,200 rpm and at 37° C. for 5 minutes   c. Thermomixer at 1,200 rpm and at 25° C. for 15 minutes       

     11. The tube was briefly centrifuged and kept at room temperature. 
     12. In a new 1.5-mL LoBind tube, the following reagents depicted in Table 3 were pipetted: 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 EXTENSION ENZYME MIX 
               
            
           
           
               
               
               
               
            
               
                   
                 For 1 
                 For 1 library 
                 For 2 libraries 
               
               
                   
                 library 
                 with 50% 
                 with 30% 
               
               
                 Kit Component 
                 (μL) 
                 overage (μL) 
                 overage (μL) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 10 mM dNTP 
                 8 
                 12 
                 20 
               
               
                 (Cat. No. 650000077) 
                   
                   
                   
               
               
                 Bead RT/PCR Enhancer 
                 12 
                 18 
                 31 
               
               
                 (Cat. No. 91-1082) 
                   
                   
                   
               
               
                 WTA Extension Enzyme 
                 6 
                 9 
                 16 
               
               
                 (Cat. No. 91-1117) 
                   
                   
                   
               
               
                 Total 
                 26 
                 39 
                 67 
               
               
                   
               
            
           
         
       
     
     13. The Extension Enzyme Mix was pipet-mixed. 
     14. 26 μL of the Extension Enzyme Mix was pipetted into the sample tube containing the beads (for a total volume of 200 μL) and kept at room temperature until ready. 
     15. The thermomixer was programmed as follows: a. 1,200 rpm and at 25° C. for 10 minutes; b. 1,200 rpm and at 37° C. for 15 minutes; c. 1,200 rpm and at 45° C. for 10 minutes; and d. 1,200 rpm and at 55° C. for 10 minutes. The ramp rates were set at maximal and set “Time Mode” to “Temp Control” before the program began. 
     16. The tube from step 14 was placed in the thermomixer. The tube was removed after the program is finished. 
     While the thermomixer program is running, AbSeq PCR1 was begun as described in the following Performing AbSeq PCR1 section. 
     17. The tube was placed in a 1.5-mL tube magnet and the supernatant was removed. 
     18. The tube was removed from the magnet and the beads were resuspended in 205 μL of Elution Buffer using a P200 pipette. 
     19. To denature the random priming products off the beads, the user pipetted to resuspend the beads. Then the user: a. incubated the sample at 95° C. in a heat block for 5 minutes (no shaking); and b. placed the tube in a thermomixer at any temperature for 10 seconds at 1,200 rpm to resuspend the beads. 
     20. The tube was placed in a 1.5-mL tube magnet. 200 μL of the supernatant containing the Random Primer Extension Product (RPE Product) was immediately transferred to a new 1.5-mL LoBind tube and kept at room temperature. 
     21. 200 μL of cold Bead Resuspension Buffer was pipetted to the tube with leftover beads. Gentle resuspension of the beads was performed by pipet-mixing (not vortexing). The beads were stored at 4° C. in the pre-amplification workspace for up to 3 months. 
     Performing AbSeq PCR1 
     Amplification of AbSeq products through PCR was performed as described in this section. 
     1. In the pre-amplification workspace, the reagents depicted in Table 4 were pipetted into a new 1.5-mL LoBind tube on ice. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 ABSEQ PCR1 REACTION MIX 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 For 1 
                 For 1 library 
               
               
                   
                   
                 library 
                 with 20% 
               
               
                   
                 Component 
                 (μL) 
                 overage (μL) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 PCR MasterMix 
                 100 
                 120 
               
               
                   
                 (Cat. No. 91-1118) 
                   
                   
               
               
                   
                 Universal Oligo 
                 10 
                 12 
               
               
                   
                 (Cat. No. 650000074) 
                   
                   
               
               
                   
                 Bead RT/PCR Enhancer 
                 12 
                 14.4 
               
               
                   
                 (Cat. No. 91-1082) 
                   
                   
               
               
                   
                 AbSeq PCR1 Primer 
                 10 
                 12 
               
               
                   
                 (Cat. No. 91-1086) 
                   
                   
               
               
                   
                 Total 
                 132 
                 158.4 
               
               
                   
                   
               
            
           
         
       
     
     2. Gentle vortex mixing and brief centrifuging were followed by placing back on ice. 
     3. In a new 1.5-mL tube, 132 μL of the AbSeq PCR1 reaction mix was pipetted. 
     Next, the addition of 68 μl of the AbSeq product from step 8 from Performing random priming and extension (RPE) on BD Rhapsody Cell Capture Beads with cDNA was conducted. Pipet-mixing 10 times was performed (not vortexing). 
     4. 50 μL AbSeq reaction was pipetted into each of four 0.2-mL PCR tubes. The transfer of any residual mix to one of the tubes was done. 
     5. The reaction mix was brought to the post-amplification workspace. 
     6. The thermal cycler was programmed as depicted in Table 5 and Table 6. The fast cycling mode was not used. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 PCR CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                 Step 
                 Cycles 
                 Temperature 
                 Time 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Hot start 
                 1 
                 95° C. 
                 3 
                 min 
               
               
                 Denaturation 
                 10-14* 
                 95° C. 
                 30 
                 s 
               
               
                 Annealing 
                   
                 60° C. 
                 30 
                 s 
               
               
                 Extension 
                   
                 72° C. 
                 1 
                 min 
               
               
                 Final extension 
                 1 
                 72° C. 
                 5 
                 min 
               
            
           
           
               
               
               
               
            
               
                 Hold 
                 1 
                  4° C. 
                 ∞ 
               
               
                   
               
               
                 *Suggested PCR cycles might need to be optimized for different cell types and cell number. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 SUGGESTED NUMBER OF PCR CYCLES 
               
            
           
           
               
               
               
            
               
                   
                 Number of 
                 Suggested PCR cycles 
               
               
                   
                 cells in PCR1 
                 for resting PBMCs 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 500 
                 14 
               
               
                   
                 1,000 
                 13 
               
               
                   
                 2,500 
                 12 
               
               
                   
                 5,000 
                 11 
               
               
                   
                 10,000 
                 10 
               
               
                   
                   
               
            
           
         
       
     
     In some instances, the PCR was run overnight. 
     7. After PCR has started, the user proceeded to step 17 of the Performing random priming and extension (RPE) on BD Rhapsody Cell Capture Beads with cDNA section. 
     8. After PCR, the tubes were briefly centrifuged. 
     9. Pipet-mixing was performed and the four reactions were combined into a new 1.5-mL LoBind tube. 
     Purifying RPE Product 
     This section describes the performance of a single-sided AMPure cleanup, which removes primer dimers and other small molecular weight by-products. The final product is purified single-stranded DNA. In some embodiments an additional cleanup is performed in instances of low cell input (&lt;5,000 cells) to ensure maximum removal of the unwanted small molecular weight products before the next PCR. The purification was performed in the pre-amplification workspace. 
     1. In a new 15-mL conical tube, 10 mL of fresh 80% (v/v) ethyl alcohol was prepared by pipetting 8.0 mL of absolute ethyl alcohol to 2.0 mL of nuclease-free water (from major supplier). The tube was vortexed for 10 seconds. Fresh 80% ethyl alcohol was made and used within 24 hours. 
     2. Agencourt AMPure XP magnetic beads were brought to room temperature (15° C. to 25° C.). The AMPure XP magnetic beads were vortexed at high speed for 1 minute until the beads were fully resuspended. 
     3. 360 μL of AMPure XP magnetic beads were pipetted into the tube containing the 200 μL of RPE product supernatant. Pipet-mixing was performed at least 10 times, then briefly centrifuged. 
     4. The suspension was incubated at room temperature for 10 minutes. 
     5. The suspension was placed on the 1.5-mL tube magnet for 5 minutes. The supernatant was removed. 
     6. Keeping the tube on the magnet, 1 mL of fresh 80% ethyl alcohol was gently added to the tube. 
     7. The sample was incubated on the magnet for 30 seconds. The supernatant was removed. 
     8. The 80% ethyl alcohol wash was repeated for a total of two washes. 
     9. Keeping the tube on the magnet, a P20 pipette was used to remove and any residual supernatant was discarded from the tube. 
     10. The beads were air-dried at room temperature for 5 minutes or until the beads no longer looked glossy. 
     11. The tube was removed from the magnet and 40 μL of Elution Buffer was pipetted into the tube. The suspension was pipet-mixed at least 10 times until the beads are fully suspended. 
     12. The sample was incubated at room temperature for 2 minutes. The tube was briefly centrifuged to collect the contents at the bottom. 
     13. The tube was placed on the magnet until the solution was clear, usually 30 seconds. 
     14. The eluate (˜40 L) was pipetted to a new PCR tube. This is the purified RPE product. 
     For samples with low cell input (e.g., starting with fewer than 5,000 PBMCs), the user proceed to step 15 for an additional round of AMPure XP magnetic purification. 
     Additional RPE Purification Steps for Cell Input &lt;5,000 PBMC Cells 
     15. To the tube from step 14, the purified RPE product volume was brought up to 100 μL with nuclease-free water and transferred to a 1.5-mL LoBind tube. The final volume was exactly 100 μL to achieve the desired size selection of the purified RPE product. 
     16. Pipet-mixing 10 times was performed, then briefly centrifuged. 
     17. 180 μL of AMPure XP magnetic beads was pipetted into the tube containing 100 μL of eluted RPE product from the first round of purification. 
     18. Pipet-mixing 10 times was performed, then briefly centrifuged. 
     19. Step 4 through step 14 was repeated once more, resulting in a total of two rounds of purification. 
     20. Elution into a new PCR tube (˜40 L). 
     The RPE product could be stored in a LoBind tube on ice or at 4° C. for up to 24 hours until PCR. 
     Performing RPE PCR 
     This section describes the generation of more RPE product through PCR amplification, so that there are multiple copies of each random-primed molecule. 
     1. In the pre-amplification workspace, in a new 1.5-mL LoBind tube, the following components listed in Table 7 are pipetted: 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 RPE PCR MIX 
               
            
           
           
               
               
               
               
            
               
                   
                 For 1 
                 For 1 library 
                 For 2 libraries 
               
               
                   
                 library 
                 with 20% 
                 with 10% 
               
               
                 Kit component 
                 (μL) 
                 overage (μL) 
                 overage (μL) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 PCR MasterMix 
                 60 
                 72 
                 132 
               
               
                 (Cat. No. 91-1118) 
                   
                   
                   
               
               
                 Universal Oligo 
                 10 
                 12 
                 22 
               
               
                 (Cat. No. 650000074) 
                   
                   
                   
               
               
                 WTA Amplification  
                 10 
                 12 
                 22 
               
               
                 Primer 
                   
                   
                   
               
               
                 (Cat. No. 91-116) 
                   
                   
                   
               
               
                 Total 
                 80 
                 96 
                 176 
               
               
                   
               
            
           
         
       
     
     2. 80 μL of the RPE PCR Mix was added to the tube with the 40 μL of purified RPE product. Pipet-mixing was performed 10 times. 
     3. The RPE PCR reaction mix was split into two PCR tubes with 60 μL of reaction mix per tube. 
     4. The reaction was brought to the post-amplification workspace and the following PCR program in Table 8 was run. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 PCR CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                 Step 
                 Cycles 
                 Temperature 
                 Time 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Hot start 
                 1 
                 95° C. 
                 3 
                 min 
               
               
                 Denaturation 
                 Refer to the 
                 95° C. 
                 30 
                 s 
               
               
                 Annealing 
                 following table, 
                 60° C. 
                 1 
                 min 
               
               
                 Extension 
                 Suggested number 
                 72° C. 
                 1 
                 min 
               
               
                   
                 of PCR cycles.* 
                   
                   
                   
               
               
                 Final  
                 1 
                 72° C. 
                 2 
                 min 
               
               
                 extension 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Hold 
                 1 
                  4° C. 
                 ∞ 
               
               
                   
               
               
                 *Suggested PCR cycles might need to be optimized for different cell types and cell number. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 SUGGESTED NUMBER OF PCR CYCLES 
               
            
           
           
               
               
               
            
               
                   
                 Number of 
                 Suggested PCR cycles 
               
               
                   
                 cells in RPE PCR 
                 for resting PBMCs 
               
               
                   
                   
               
               
                   
                 1,000-9,999 
                 13 
               
               
                   
                 10,000 
                 12 
               
               
                   
                   
               
            
           
         
       
     
     5. When the RPE PCR reaction was complete, briefly centrifugation was performed to collect the contents at the bottom of the tubes. 
     Purification of the RPE PCR Amplification Product (Single-Sided Cleanup) 
     This section the performance a single-sided AMPure cleanup to remove unwanted small molecular weight products from the RPE products. The final product is purified double-stranded DNA (˜200-2,000 bp). The purification was performed in the post-amplification workspace. 
     1. The two RPE PCR reactions were combined into a new 1.5-mL tube. 
     2. The tubes with the RPE PCR product were briefly centrifuged. 
     3. The AMPure XP magnetic beads were brought to room temperature (15° C. to 25° C.). Vortexing of the AMPure XP magnetic beads at high speed was performed for 1 minute until the beads were fully resuspended. 
     4. 120 μL of AMPure XP magnetic beads were pipetted into the tube containing 120 μL of RPE PCR product. Pipet-mixing was performed at least 10 times, then briefly centrifuged the samples. 
     5. The suspension was incubated at room temperature for 5 minutes. 
     6. The suspension was placed on the strip tube magnet for 3 minutes. The supernatant was discarded. 
     7. Keeping the tubes on the magnet, 200 μL of fresh 80% ethyl alcohol was gently pipetted to the tube. 
     8. The samples were incubated for 30 seconds on the magnet. The supernatant was removed. 
     9. The 80% ethyl alcohol wash was repeated for a total of two washes. 
     10. Keeping the tubes on the magnet, a small-volume pipette was used to remove any residual supernatant from the tube. 
     11. Air-drying of the beads at room temperature was performed for 5 minutes or until the beads no longer looked glossy. 
     12. The tube was removed from the magnet and 40 μL of Elution Buffer was pipetted into the tube. Pipet-mixing the suspension at least 10 times was performed until beads were fully suspended. 
     13. The samples were incubated at room temperature for 2 minutes. The tubes were briefly centrifuged to collect the contents at the bottom. 
     14. The tubes were placed on the magnet until the solution was clear, usually 30 seconds. 
     15. The eluate (˜40 L) was pipetted into new 1.5-mL LoBind tubes. The RPE PCR product was then ready for Index PCR. At this point, the RPE PCR libraries can be stored at −20° C. for up to 6 months or 4° C. for up to 6 weeks. 
     16. Quantification and performance of quality control of the RPE PCR products was done with a Qubit Fluorometer using the Qubit dsDNA HS Assay and the following systems: Agilent 2100 Bioanalyzer using the Agilent High Sensitivity DNA Kit and/or Agilent 4200 TapeStation system using the Agilent High Sensitivity D5000 ScreenTape Assay. 
     a. The expected concentration from the Qubit Fluorometer is 0.5 to 10 ng/L. 
     b. The Bioanalyzer/TapeStation trace should show a broad peak from 200 to 2,000 bp. The concentration from 150 to 600 bp can be used to calculate how much template to add into Index PCR. See boxed regions in the sample trace images  FIGS.  18 A- 18 B , which depict an exemplary Sample Bioanalyzer High Sensitivity DNA trace of RPE PCR product ( FIG.  18 A ) and an exemplary Sample TapeStation High Sensitivity D5000 trace of RPE PCR product. 
     Although there can be products &gt;600 bp, these products should be removed in the double-sided cleanup after the next PCR. 
     Purifying AbSeq PCR1 Products 
     This section describes the performance of a single-sided AMPure cleanup to remove primer dimers from the AbSeq PCR1 products. The final product is purified double-stranded DNA. The purification was performed in the post-amplification workspace. 
     1. In a new 5.0-mL LoBind tube, 5 mL fresh 80% (v/v) ethyl alcohol was prepared by combining 4.0 mL absolute ethyl alcohol, molecular biology grade with 1.0 mL nuclease-free water. The tube was vortexed for 10 seconds to mix. Fresh 80% ethyl alcohol was made, and was used within 24 hours. 
     2. The AMPure XP magnetic beads were brought to room temperature (15° C. to 25° C.). Vortexing at high speed for 1 minute was performed until the beads were fully resuspended. 
     3. 280 μL AMPure XP beads was pipetted into a tube with 200 μL AbSeq PCR1. Pipet-mixing was performed 10 times. 
     4. Incubation at room temperature (15° C. to 25° C.) for 5 minutes was performed. 
     5. The 1.5-mL LoBind tube was placed on the magnet for 5 minutes. The supernatant was removed. 
     6. Keeping the tube on the magnet, 500 μL of fresh 80% ethyl alcohol was gently added, and incubated for 30 seconds. The supernatant was removed. 
     7. Step 6 was repeated once for two washes. 
     8. Keeping the tube on the magnet, a small-volume pipette was used to remove and discard the residual supernatant from tube. 
     9. The beads were allowed to air-dry at room temperature (15° C. to 25° C.) for 5 minutes. 
     10. The tube was removed from the magnet and the bead pellet was resuspended in 30 μL of Elution Buffer. Vigorously pipet-mixing was performed until the beads were uniformly dispersed. Small clumps were found to not affect the performance. 
     11. After incubating at room temperature (15° C. to 25° C.) for 2 minutes, briefly centrifugation was performed. 
     12. The tube was placed on the magnet until the solution is clear, usually &lt;30 seconds. 
     13. The eluate (˜30 L) was pipetted into a new 1.5-mL LoBind tube (purified AbSeq PCR1 products) and could be stored at 2° C. to 8° C. before proceeding within 24 hours or at −25° C. to −15° C. for up to 6 months. 
     Quantifying BD AbSeq PCR1 Products 
     1. The yield of the largest peak of the BD AbSeq/Sample Tag PCR1 products (˜170 bp) was measured by using the Agilent Bioanalyzer with the High Sensitivity Kit follow the manufacturer&#39;s instructions. 
     2. An aliquot of BD AbSeq/Sample Tag PCR1 products was diluted to 0.1-1.1 ng/L with Elution Buffer (Cat. No. 91-1084) before index PCR of BD AbSeq PCR1 products. 
     Performing WTA Index PCR 
     This section describes the generation of mRNA libraries compatible with the Illumina sequencing platform, by adding full-length Illumina sequencing adapters and indices through PCR. This procedure was performed in the post-amplification workspace. 
     1. The RPE PCR products was diluted with Elution Buffer such that the concentration of the 150-600 bp peak was 2 nM. If the product concentration was &lt;2 nM, the protocol was continued without dilution. For example: If the Bioanalyzer measurement of the 150-600 bp peak is 2 nM, then dilute the sample threefold with Elution Buffer to 2 nM. 
     2. In a new 1.5-mL tube, the following components depicted in Table 10 were pipetted: 
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 WTA INDEX PCR MIX 
               
            
           
           
               
               
               
               
            
               
                   
                 For 1 
                 For 1 library 
                 For 2 libraries 
               
               
                   
                 library 
                 with 20% 
                 with 10% 
               
               
                 Kit component 
                 (μL) 
                 overage (μL) 
                 overage (μL) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 PCR MasterMix 
                 25 
                 30 
                 55 
               
               
                 (Cat. No. 91-1118) 
                   
                   
                   
               
               
                 Library Forward Primer 
                 5 
                 6 
                 11 
               
               
                 (Cat. No. 91-1085) 
                   
                   
                   
               
               
                 Library Reverse  
                 5 
                 6 
                 — 
               
               
                 Primer (1-4)* 
                   
                   
                   
               
               
                 (Cat. Nos. 650000080, 
                   
                   
                   
               
               
                 650000091-93) 
                   
                   
                   
               
               
                 Nuclease-free water 
                 5 
                 6 
                 11 
               
               
                 (Cat. No. 650000076) 
                   
                   
                   
               
               
                 Total 
                 40 
                 48 
                 77 
               
               
                   
               
               
                 *For more than one library, use different Library Reverse Primers for each library. 
               
            
           
         
       
     
     3. After gently vortex mixing, it was briefly centrifuged and placed back on ice. 
     4. In a new 0.2-mL PCR tube, the WTA Index PCR Mix was combined with diluted RPE PCR products as follows: 
     a. For 1 sample, combined 40 μL of WTA Index PCR Mix with 10 μL of 2 nM of RPE PCR products. 
     b. For multiple samples, combined 35 μL of WTA Index PCR Mix with 5 μL of Library Reverse Primer and 10 μL of 2 nM of RPE PCR products. 
     5. Pipet-mixing 10 times was performed. 
     6. The PCR program depicted in Tables 11-12 was run: 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 PCR CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                 Step 
                 Cycles 
                 Temperature 
                 Time 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Hot start 
                 1 
                 95° C. 
                 3 
                 min 
               
               
                 Denaturation 
                 Refer to the 
                 95° C. 
                 30 
                 s 
               
               
                 Annealing 
                 following table, 
                 60° C. 
                 30 
                 s 
               
               
                 Extension 
                 Suggested number 
                 72° C. 
                 30 
                 s 
               
               
                   
                 of PCR cycles. 
                   
                   
                   
               
               
                 Final  
                 1 
                 72° C. 
                 1 
                 min 
               
               
                 extension 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Hold 
                 1 
                  4° C. 
                 ∞ 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 SUGGESTED NUMBER OF PCR CYCLES 
               
            
           
           
               
               
               
            
               
                   
                 Concentration of diluted 
                 Suggested number 
               
               
                   
                 RPE PCR products 
                 of PCR cycles 
               
               
                   
                   
               
               
                   
                 1 to &lt; 2 nM 
                 9 
               
               
                   
                 2 nM 
                 8 
               
               
                   
                   
               
            
           
         
       
     
     If the concentrations of diluted RPE PCR products are &lt;1 nM, additional PCR cycles can be performed as needed. The PCR can be run overnight. 
     7. When the WTA Index PCR is complete, briefly centrifugation was performed to collect the contents at the bottom of the tubes. 
     Purification of the WTA Index PCR Product (Dual-Sided Cleanup) 
     This section describes the performance of a double-sided AMPure cleanup to ensure that the library is at a proper size (250-1,000 bp) for Illumina sequencing. The final product is purified double-stranded DNA with full-length Illumina adapter sequences. The purification was performed in the post-amplification workspace. 
     1. 60 μL of nuclease-free water was added to the WTA Index PCR product for a final volume of 110 μL. 
     2. 100 μL of WTA Index PCR product was transferred into a new 0.2-mL PCR tube. 
     3. AMPure XP magnetic beads were brought to room temperature (15° C. to 25° C.). The AMPure XP magnetic beads were vortexed at high speed for 1 minute. The beads should appear homogeneous and uniform in color. 
     4. 60 μL of AMPure XP magnetic beads was added to the 0.2-mL PCR tube from step 2. 
     5. After pipet-mixing at least 10 times, the samples were briefly centrifuged. 
     6. The suspensions were incubated at room temperature for 5 minutes, then placed on the 0.2-mL strip tube magnet for 2 minutes. 
     7. 15 μL of AMPure XP magnetic beads was pipetted into a different strip tube. 
     8. While the strip tube in step 6 is still on the magnet, carefully, without disturbing the beads, the 160 μL of supernatant was removed and transferred into the 0.2-mL strip tube with AMPure XP magnetic beads (from step 7) and pipet-mixed 10 times. 
     9. The suspension was incubated at room temperature for 5 minutes, then the new tube was placed on a 0.2-mL tube magnet for 1 minute. 
     10. While on the magnet, the user carefully removed and appropriately discarded only the supernatant without disturbing the AMPure XP magnetic beads. 
     11. Keeping the tubes on the magnet, the user gently pipetted 200 μL of fresh 80% ethyl alcohol into the tubes. 
     12. The samples were incubated for 30 seconds on the magnet. 
     13. While on the magnet, the user carefully removed and appropriately discarded only the supernatant without disturbing the AMPure XP magnetic beads. 
     14. The 200 μL of fresh 80% ethyl alcohol wash was repeated for a total of two washes. 
     15. Keeping the tubes on the magnet, a small-volume pipette was used to remove any residual supernatant from the tube. 
     16. The tubes were left open on the magnet to dry the AMPure XP magnetic beads at room temperature for −1 minute. Care was taken to not over-dry the AMPure XP magnetic beads. 
     17. 30 μL of Elution Buffer was pipetted into the tubes and pipet-mixed to completely resuspend the AMPure XP magnetic beads. 
     18. The samples were incubated at room temperature for 2 minutes. 
     19. The tubes were briefly centrifuged to collect the contents at the bottom. 
     20. The tubes were placed on the magnet until the solution was clear, usually 30 seconds. 
     21. The eluate (˜30 L) was pipetted into new 1.5-mL LoBind tubes. The WTA Index PCR eluate is the final sequencing libraries. Index PCR libraries could be stored at −20° C. for up to 6 months until sequencing. 
     22. Quantification and performance of quality control of the Index PCR libraries was done with a Qubit Fluorometer using the Qubit dsDNA HS Assay and either of the following systems: Agilent 2100 Bioanalyzer using the Agilent High Sensitivity DNA Kit or Agilent 4200 TapeStation system using the Agilent High Sensitivity D1000 or D5000 ScreenTape Assay. 
     a. The expected concentration from the Qubit Fluorometer is &gt;1 ng/μL. 
     b. The Bioanalyzer/TapeStation trace should show a peak from 250-1,000 bp. See the sample trace images depicted in  FIGS.  19 A- 19 B . 
     If a ˜165 bp peak is observed in  FIGS.  19 A- 19 B , such as the peak shown in  FIG.  20   , a second round of AMPure XP magnetic purification is recommended. See Additional WTA Index PCR purification steps in the following section.  FIGS.  19 A- 19 B  depict an exemplary Sample Bioanalyzer High Sensitivity DNA trace of WTA Index PCR product ( FIG.  18 A ) and an exemplary Sample TapeStation High Sensitivity D5000 trace of WTA Index PCR product.  FIG.  20    depicts an exemplary sample bioanalyzer high-sensitivity DNA trace for an Index PCR product with an observable peak at 165 bp. 
     Additional WTA Index PCR Purification Steps 
     If a 165 bp peak is observed in the Bioanalyzer/TapeStation traces (e.g.,  FIGS.  19 A- 19 B ), a second round of AMPure XP magnetic purification is recommended. 
     1. To the tube from step 21, the total purified WTA Index PCR elute volume was brought up to 100 μL with nuclease-free water. The final volume was exactly 100 μL to achieve the desired size selection of the purified WTA Index PCR library. 
     2. Pipet-mixing was performed 10 times, then briefly centrifuged. 
     3. 75 μL of AMPure XP magnetic beads was pipetted into the tube containing 100 μL of eluted RPE product from the first round of purification. 
     4. Pipet-mixing was performed 10 times, then briefly centrifuged. 
     5. Repeat step 9 through above once more, resulting in a total of two rounds of purification. 
     6. The elute (˜30 L) was collected to a new PCR tube. 
     7. The quality control step was repeated (step 22 above). 
     The Index PCR libraries can be stored at −20° C. for up to 6 months until sequencing. 
     Performing AbSeq Index PCR 
     This section describes the generation of AbSeq libraries compatible with the Illumina sequencing platform by adding full-length Illumina sequencing adapter and indices through PCR. 
     1. In pre-amplification workspace, the reagents depicted in Table 13 were pipetted into a new 1.5-mL LoBind Tube on ice. In some embodiments, for a single cartridge or sample, the user employed the same index for both the WTA and AbSeq Index PCR products for that cartridge or sample. Otherwise, different library reverse primers can be used for WTA and AbSeq Index PCR products. 
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 ABSEQ INDEX PCR MIX 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 For 1 
                 For 1 library 
               
               
                   
                   
                 library 
                 with 20% 
               
               
                   
                 Kit Component 
                 (μL) 
                 overage (μL) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 PCR MasterMix 
                 25 
                 30 
               
               
                   
                 (Cat. No. 91-1118) 
                   
                   
               
               
                   
                 Library Forward Primer 
                 2 
                 2.4 
               
               
                   
                 (Cat. No. 91-1085) 
                   
                   
               
               
                   
                 Library Reverse Primer (1-4)* 
                 2 
                 2.4 
               
               
                   
                 (Cat. Nos. 650000080, 
                   
                   
               
               
                   
                 650000091-93) 
                   
                   
               
               
                   
                 *For more than one library,  
                   
                   
               
               
                   
                 use different Library Reverse  
                   
                   
               
               
                   
                 Primers for each AbSeq library. 
                   
                   
               
               
                   
                 Nuclease-free water 
                 18 
                 21.6 
               
               
                   
                 (Cat. No. 650000076) 
                   
                   
               
               
                   
                 Total 
                 47 
                 56.4 
               
               
                   
                   
               
            
           
         
       
     
     2. After gentle vortex mixing and brief centrifugation, it was placed back on ice. 
     3. The AbSeq Index PCR mix was brought to the post-amplification workspace. 
     4. 3.0 μL of 0.1-1.1 ng/μL products was pipetted into 47 μL AbSeq Index PCR mix. 
     5. Gently vortexed and briefly centrifuged. 
     6. The thermal cycler was programmed as shown in Tables 14-15. Fast cycling mode was not used. The PCR could run overnight. 
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 PCR CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                 Step 
                 Cycles 
                 Temperature 
                 Time 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Hot start 
                 1 
                 95° C. 
                 5 
                 min 
               
               
                 Denaturation 
                 Refer to the 
                 95° C. 
                 30 
                 s 
               
               
                 Annealing 
                 following table, 
                 60° C. 
                 30 
                 s 
               
               
                 Extension 
                 Suggested number 
                 72° C. 
                 30 
                 s 
               
               
                   
                 of PCR cycles. 
                   
                   
                   
               
               
                 Final  
                 1 
                 72° C. 
                 1 
                 min 
               
               
                 extension 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Hold 
                 1 
                  4° C. 
                 ∞ 
               
               
                   
               
               
                 * Cycle number varies based on the concentration of the RPE PCR products. 
               
            
           
         
       
     
                     TABLE 15                  SUGGESTED NUMBER OF PCR CYCLES                             Conc. index PCR input for   Suggested number           AbSeq libraries (ng/μL)   of PCR cycles                       0.5-1.1   6           0.25-0.5    7            0.1-0.25   8                        
Purifying AbSeq Index PCR Products
 
     This section describes the performance of a single-sided AMPure cleanup to remove primer dimers from the AbSeq Index PCR products. The final product is purified double-stranded DNA with full-length Illumina sequences. The purification was performed in the post-amplification workspace. 
     1. The AMPure XP beads were brought to room temperature (15° C. to 25° C.) and vortexed at high speed for 1 minute until the beads were fully resuspended. 
     2. The AbSeq Index PCR products were briefly centrifugated. 
     3. To 50.0 μL of AbSeq Index PCR products, 40 μL of AMPure beads was pipetted. 
     4. Pipet-mixing was performed 10 times and incubated at room temperature (15° C. to 25° C.) for 5 minutes. 
     5. Each tube was placed on the strip tube magnet for 3 minutes. The supernatant was removed. 
     6. Keeping the tubes on the magnet, gently added 200 μL of fresh 80% ethyl alcohol into each tube and incubated for 30 seconds. Removed the supernatant. 
     7. Step 6 was repeated for a total of two washes. 
     8. Keeping the tube on the magnet, a small-volume pipette was used to remove and discard the residual supernatant from the tube. 
     9. The beads were allowed to air-dry at room temperature (15° C. to 25° C.) for 3 minutes. 
     10. The tube was removed from the magnet and resuspended each bead pellet in 30 μL of Elution Buffer. Pipet-mixed until the beads were fully resuspended. 
     11. Incubation at room temperature (15° C. to 25° C.) for 2 minutes and briefly centrifuged. 
     12. The tube was placed on the magnet until the solution is clear, usually &lt;30 seconds. 
     13. The entire eluate (˜30 μL) was pipetted to new 1.5-mL LoBind tubes (final sequencing libraries). Storage is possible at −25° C. to −15° C. for up to 6 months until final sequencing. 
     14. The concentration was estimated by quantifying 2 μL of the final sequencing library with a Qubit Fluorometer using the Qubit dsDNA HS Kit to obtain an approximate concentration of PCR products to dilute for quantification on an Agilent 2100 Bioanalyzer or an Agilent 4200 TapeStation system using the Agilent High Sensitivity D1000 or D5000 ScreenTape Assay (following the manufacturer&#39;s instructions). The expected concentration of the libraries is &gt;1.5 ng/μL. The AbSeq library should show a peak of 290 bp. 
     Sequencing Protocol Embodiments 
     In some embodiments, for a NextSeq High or Mid Output run and MiniSeq High or Mid Output run, the flow cell is loaded at a concentration between 1-1.2 pM with 20% PhiX for a sequencing run. Sequencing depth of the WTA mRNA libraries can vary depending on whether the sample contains high- or low-content RNA cells. In some embodiments, for resting PBMCs: (i) 10,000 reads per cell for shallow sequencing, with genes per cell and UMI per cell detected generally lower but can be useful for cell type identification; (ii) 50,000 reads per cell for moderate sequencing; and/or (iii) 100,000 reads per cell for deep sequencing to harvest the majority of UMIs in the library. 
     In some embodiments, with regards to the sequencing amount for AbSeq libraries, the amount of sequencing needed for BD AbSeq libraries will vary depending on application, BD AbSeq panel plexy, and cell type. It was observed that using 40,000 sequencing reads per cell for 40-plex BD AbSeq libraries prepared from resting PBMCs achieves an RSEC sequencing depth of ˜2. 
     Example 5 
     AbSeq Protocol Modification Test: Separate PCR1 Reactions for AbSeq and mRNA Targeted Assays 
     This example provides validation for the methods and compositions provided herein for separate PCR workflows for protein quantitation and RNA quantitation. Unwanted products can be generated in PCR1, especially when cellular component binding reagent oligonucleotides (e.g., AbSeq Ab-oligos) are present, and can to be due to synergy between: (i) primers non-specifically binding to the bead UMI; (ii) overlapping 3′ ends of the universal oligo (forward primer) and the AbSeq PCR1 (reverse primer); and/or (iii) thermal cycling conditions that are non-ideal for the universal amplification for Ab-oligos (3 min annealing @ 60 C). Both bead-based and assay-based strategies have been investigated to stop unwanted product generation. One novel strategy proposed herein is to amplify mRNA targets and Ab-oligos separately, such that the PCR reactions can be optimized to its template. 
     The workflows disclosed herein were experimentally tested to determine whether the same sensitivity of oligo detection can be achieved from separate amplification from mRNA and proxy oligo targets (isolated from denaturation of Rhapsody beads prior to PCR1) versus the standard co-amplification approach. The separate oligo proxy PCR will be tested with the current cycling conditions. Given the feasibility of this approach, additional optimization of Ab-oligo PCR1 cycling conditions to rid of unwanted products can be done. 
     Table 16 depicts the experimental conditions tested. Oligo proxy (pool  8 , dynamic range: 100 to 100,000 copies (˜892K total per oligo), 40-plex+UHRR. 500 cell equivalents were employed with updated Ampure cleanup strategy. 5 min of 95° C. denaturation was performed in 56 uL of bead resuspension buffer.  FIG.  21    depicts workflow for the experimental conditions tested. 
     
       
         
           
               
             
               
                 TABLE 16 
               
             
            
               
                   
               
               
                 EXPERIMENTAL CONDITIONS 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                   
                 PCR1  
               
               
                   
                 PCR1 
                 PCR1 
                 PCR1 
                 cleanup 
               
               
                 Condition 
                 template 
                 primers 
                 cycles 
                 strategy 
               
               
                   
               
               
                 Ctrl500 
                 Rhapsody 
                 AbSeq PCR1; 
                 500:15 
                 0.7× mRNA/ 
               
               
                 (“Ctrl”) 
                 (“Rhap”)  
                 Human  
                   
                 1.2× 
               
               
                   
                 beads 
                 Immune 
                   
                 Ab-oligo 
               
               
                   
                   
                 Response  
                   
                   
               
               
                   
                   
                 N1 
                   
                   
               
               
                 SupA500 
                 Supernatant 
                 AbSeq PCR1 
                 500:16 
                 1.2×  
               
               
                 (“SupA”) 
                 from  
                   
                   
                 Ab-oligo 
               
               
                   
                 denatured 
                   
                   
                   
               
               
                   
                 Rhapsody  
                   
                   
                   
               
               
                   
                 bead 
                   
                   
                   
               
               
                 OnBeadA500 
                 Denatured 
                 AbSeq PCR1; 
                 500:16 
                 0.7× mRNA/ 
               
               
                 (“OnBeadA”) 
                 Rhapsody  
                 Human  
                   
                 1.2× 
               
               
                   
                 beads 
                 Immune 
                   
                 Ab-oligo 
               
               
                   
                   
                 Response  
                   
                   
               
               
                   
                   
                 N1 
                   
                   
               
               
                 SupB500 
                 Supernatant 
                 AbSeq PCR1 
                 500:16 
                 1.2×  
               
               
                 (“SupB”) 
                 from  
                   
                   
                 Ab-oligo 
               
               
                   
                 denatured 
                   
                   
                   
               
               
                   
                 Rhapsody  
                   
                   
                   
               
               
                   
                 beads 
                   
                   
                   
               
               
                 OnBeadB500 
                 Denatured 
                 Human  
                 500:16 
                 0.7× mRNA/ 
               
               
                 (“OnBeadB”) 
                 Rhapsody  
                 Immune 
                   
                 1.2× 
               
               
                   
                 bead 
                 Response  
                   
                 “small stuff” 
               
               
                   
                   
                 N1 
               
               
                   
               
            
           
         
       
     
       FIGS.  22 A- 22 J  depict PCR1 traces of conditions Control mRNA ( FIG.  22 A ), Control Ab-oligo ( FIG.  22 B ), On Bead A mRNA ( FIG.  22 C ), On Bead A Ab-oligo ( FIG.  22 D ), Sup A ( FIG.  22 E ), On Bead B mRNA ( FIG.  22 F ), On Bead B “junk” ( FIG.  22 G ), and Sup B ( FIG.  22 H ). Table 17 depicts the experimental conditions tested. 
     
       
         
           
               
             
               
                 TABLE 17 
               
             
            
               
                   
               
               
                 EXPERIMENTAL CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                   
                 PCR1 
                 PCR1 
                 PCR1 cleanup 
               
               
                 Condition 
                 template 
                 primers 
                 strategy 
               
               
                   
               
               
                 Ctrl 
                 Rhap beads 
                 AbSeq PCR1; 
                 0.7× mRNA/1.2× 
               
               
                   
                   
                 Human Immune 
                 Ab-oligo 
               
               
                   
                   
                 Response N1 
                   
               
               
                 Sup A 
                 Supernatant 
                 AbSeq PCR1 
                 1.2× Ab-oligo 
               
               
                   
                 from denatured 
                   
                   
               
               
                   
                 Rhap bead 
                   
                   
               
               
                 OnBead A 
                 Denatured 
                 AbSeq PCR1; 
                 0.7× mRNA/1.2× 
               
               
                   
                 Rhap bead 
                 Human Immune 
                 Ab-oligo 
               
               
                   
                   
                 Response N1 
                   
               
               
                 Sup B 
                 Supernatant 
                 AbSeq PCR1 
                 1.2× Ab-oligo 
               
               
                   
                 from denatured 
                   
                   
               
               
                   
                 Rhap bead 
                   
                   
               
               
                 OnBead B 
                 Denatured 
                 Human Immune 
                 0.7× mRNA/1.2× 
               
               
                   
                 Rhap bead 
                 Response N1 
                 “small stuff” 
               
               
                   
               
            
           
         
       
     
       FIGS.  23 A- 23 B  depict PCR1 overlays of conditions Ctrl mRNA, On Bead A mRNA, and On Bead B mRNA ( FIG.  23 A ), and PCR1 overlays of conditions Ctrl Ab-oligo, On Bead A Ab-oligo, Supernatant A, and Supernatant B ( FIG.  23 B ).  FIGS.  24 A- 24 C  depict mRNA PCR2 Traces of condition Control mRNA ( FIG.  24 A ), On Bead A mRNA ( FIG.  24 B ), and On Bead B mRNA ( FIG.  24 C ).  FIG.  25    depicts mRNA PCR2 Overlay of Ctrl mRNA, On Bead A mRNA, and On Bead B mRNA.  FIGS.  26 A- 26 D  depicts mRNA Index PCR Traces of conditions Control mRNA ( FIG.  26 A ), On Bead A mRNA ( FIG.  26 B ), and On Bead B mRNA ( FIG.  26 C ).  FIG.  27    depicts an mRNA Index PCR Overlay of conditions Ctrl mRNA, On Bead A mRNA, and On Bead B mRNA.  FIGS.  28 A- 28 D  depict AbO Index PCR Traces of conditions Control Ab-oligo ( FIG.  28 A ), On Bead A Ab-oligo ( FIG.  28 B ), Sup A ( FIG.  28 C ), and Sup B ( FIG.  28 D ).  FIG.  29    depicts an AbO Index PCR Overlay of Ctrl Ab-oligo, On Bead A Ab-oligo, Sup A, and Sup B. 
     Sequencing yield and pipeline analysis was conducted. Table 18 depicts the raw sequencing reads for the sequencing libraries obtained. The reads per cell allocated in library pooling were 10K reads per cell for mRNA and 45K reads per Ab-oligo. Uneven read allocation can require down-sampling of some AbSeq and mRNA libraries to achieve equivalent mean reads per cell. Table 19 depicts the experimental conditions tested. Tables 20-23 depicts down-sampling calculations of the experimental data. 
     
       
         
           
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 RAW READS 
               
            
           
           
               
               
               
            
               
                   
                 Library 
                 raw reads per cell achieved 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 J104CtrlABC 
                 46,223 
               
               
                   
                 J104OnBeadAABC 
                 44,195 
               
               
                   
                 J104SupAABC 
                 81,338 
               
               
                   
                 J104SupBABC 
                 23,807 
               
               
                   
                 J104CtrlRhap 
                 7,889 
               
               
                   
                 J104OnBeadARhap 
                 5,553 
               
               
                   
                 J104OnBeadBRhap 
                 7,303 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 19 
               
             
            
               
                   
               
               
                 EXPERIMENTAL CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                   
                 PCR1 
                 PCR1 
                 PCR1 cleanup 
               
               
                 Condition 
                 template 
                 primers 
                 strategy 
               
               
                   
               
               
                 Ctrl 
                 Rhapsody 
                 AbSeq PCR1; 
                 0.7× mRNA/1.2× 
               
               
                   
                 (“Rhap”)  
                 Human Immune 
                 Ab-oligo 
               
               
                   
                 beads 
                 Response N1 
                   
               
               
                 Sup A 
                 Supernatant 
                 AbSeq PCR1 
                 1.2× Ab-oligo 
               
               
                   
                 from denatured 
                   
                   
               
               
                   
                 Rhap bead 
                   
                   
               
               
                 OnBead A 
                 Denatured 
                 AbSeq PCR1; 
                 0.7× mRNA/1.2× 
               
               
                   
                 Rhap bead 
                 Human Immune 
                 Ab-oligo 
               
               
                   
                   
                 Response N1 
                   
               
               
                 Sup B 
                 Supernatant 
                 AbSeq PCR1 
                 1.2× Ab-oligo 
               
               
                   
                 from denatured 
                   
                   
               
               
                   
                 Rhap bead 
                   
                   
               
               
                 OnBead B 
                 Denatured 
                 Human Immune 
                 0.7× mRNA 
               
               
                   
                 Rhap bead 
                 Response N1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 20 
               
             
            
               
                   
               
               
                 DOWN-SAMPLING CALCULATIONS 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Pct Cellular Reads 
                 Pct Reads 
                   
                 % raw reads 
               
               
                   
                   
                 Total Reads in 
                 Pct Reads 
                 Aligned Uniquely to 
                 from Putative 
                 Useful 
                 remaining 
               
               
                   
                 Group 
                 FASTQ 
                 Filtered Out 
                 Amplicons 
                 Cells 
                 reads 
                 after filtering 
               
               
                   
               
               
                 AbSeq 
                 J104CtrlABC 
                 23,481,395 
                 4.18 
                 94.82 
                 80.69 
                 17,214,711 
                 73.3% 
               
               
                 AbSeq 
                 J104OnBeadAABC 
                 23,246,454 
                 5.89 
                 90.7 
                 78.27 
                 15,530,846 
                 66.8% 
               
               
                 AbSeq 
                 J104SupAABC 
                 41,238,263 
                 1.88 
                 94.69 
                 79.17 
                 30,333,510 
                 73.6% 
               
               
                 AbSeq 
                 J104SupBABC 
                 12,522,526 
                 2.58 
                 94.73 
                 78.56 
                  9,078,813 
                 72.5% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 21 
               
             
            
               
                   
               
               
                 DOWN-SAMPLING CALCULATIONS 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 Reads per 
                   
                   
               
               
                   
                   
                   
                   
                   
                 Least 
                 Back calc 
                 cell if 
                   
                   
               
               
                   
                   
                 Putative 
                 Useful 
                 Mean 
                 reads 
                 useful 
                 useful 
                   
                   
               
               
                   
                   
                 Cell 
                 reads/putative 
                 Reads 
                 vs. 
                 reads 
                 reads are 
                 Total reads 
                   
               
               
                   
                 Group 
                 Count 
                 cell 
                 per Cell 
                 others 
                 needed 
                 achieved 
                 needed 
                 Action 
               
               
                   
               
               
                 AbSeq 
                 J104CtrlABC 
                 508 
                 33887.23 
                 33990.32 
                  52.7% 
                 9,069,839 
                 17,854 
                 12,371,539 
                 Down-sample 
               
               
                 AbSeq 
                 J104OnBeadAABC 
                 526 
                 29526.32 
                 29592.96 
                  60.5% 
                 9,398,570 
                 17,868 
                 14,067,710 
                 Down-sample 
               
               
                 AbSeq 
                 J104SupAABC 
                 526 
                 57668.27 
                 57735.01 
                  31.0% 
                 9,408,893 
                 17,888 
                 12,791,345 
                 Down-sample 
               
               
                 AbSeq 
                 J104SupBABC 
                 507 
                 17906.93 
                 17908.33 
                 100.0% 
                 9,078,813 
                 17,907 
                 12,522,526 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 22 
               
             
            
               
                   
               
               
                 DOWN-SAMPLING CALCULATIONS 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                 Pct Cellular Reads 
                   
                   
                 % raw reads 
               
               
                   
                   
                 Total Reads in 
                 Pct Reads 
                 Aligned Uniquely to 
                 Pct Reads from 
                   
                 remaining after 
               
               
                   
                 Group 
                 FASTQ 
                 Filtered Out 
                 Amplicons 
                 Putative Cells 
                 Useful reads 
                 filtering 
               
               
                   
               
               
                 mRNA 
                 Ctrl 
                 3999904 
                 2.99 
                 91.32 
                 67.58 
                 2,394,695 
                 59.9% 
               
               
                 mRNA 
                 OnBeadA 
                 2820710 
                 3.51 
                 89.62 
                 72.63 
                 1,771,584 
                 62.8% 
               
               
                 mRNA 
                 OnBeadB 
                 3841446 
                 2.44 
                 89.3 
                 68.78 
                 2,301,867 
                 59.9% 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 23 
               
             
            
               
                   
               
               
                 DOWN-SAMPLING CALCULATIONS 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                   
                   
                 Reads per 
                   
                   
               
               
                   
                   
                   
                   
                   
                 Least 
                 Back calc 
                 cell if 
                   
                   
               
               
                   
                   
                 Putative 
                 Useful 
                 Mean 
                 reads 
                 useful 
                 useful 
                   
                   
               
               
                   
                   
                 Cell 
                 reads/putative 
                 Reads 
                 vs. 
                 reads 
                 reads are 
                 Total reads 
                   
               
               
                   
                 Group 
                 Count 
                 cell 
                 per Cell 
                 others 
                 needed 
                 achieved 
                 needed 
                 Action 
               
               
                   
               
               
                 AbSeq 
                 J104CtrlABC 
                 508 
                 33887.23 
                 33990.32 
                  52.7% 
                 9,069,839 
                 17,854 
                 12,371,539 
                 Down-sample 
               
               
                 AbSeq 
                 J104OnBeadAABC 
                 526 
                 29526.32 
                 29592.96 
                  60.5% 
                 9,398,570 
                 17,868 
                 14,067,710 
                 Down-sample 
               
               
                 AbSeq 
                 J104SupAABC 
                 526 
                 57668.27 
                 57735.01 
                  31.0% 
                 9,408,893 
                 17,888 
                 12,791,345 
                 Down-sample 
               
               
                 AbSeq 
                 J104SupBABC 
                 507 
                 17906.93 
                 17908.33 
                 100.0% 
                 9,078,813 
                 17,907 
                 12,522,526 
               
               
                   
               
            
           
         
       
     
     Sequencing Metrics of down-sampled libraries were investigated. In some embodiments, amplification of proxy oligo cDNA is less efficient than amplifying denatured proxy oligos, such as with regards to sensitivity loss, with fewer molecules counted with the approximately same number of reads achieving higher sequencing saturation (OnBeadA vs. SupA &amp; SupB).  FIGS.  30 A- 30 B  depict sequencing metrics of down-sampled libraries.  FIG.  30 A  depicts exemplary data related to the ABC metrics, AbSeq sensitivity, and AbSeq sequencing saturation of Ctrl, OnBeadA, SupA, and SupB.  FIG.  30 B  depicts exemplary data related to the mRNA metrics, mRNA sensitivity, and mRNA sequencing saturation of Ctrl, OnBeadA, and OnBeadB. A 10% decrease in mRNA mol per cell was observed in some test conditions. Approximately 17K mean molecules per bead observed (892K copies per bead expected) translates to approximately 2% efficiency. 
       FIGS.  31 A- 31 B  depict exemplary data related to proxy oligonucleotide sensitivity. Mean molecule counts of OnBeadA was reduced by 25-35% across each copy number group. Table 24 depicts experimental conditions tested. 
     
       
         
           
               
             
               
                 TABLE 24 
               
             
            
               
                   
               
               
                 EXPERIMENTAL CONDITIONS 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 PCR1 
                 PCR1 
               
               
                   
                 Condition 
                 template 
                 primers 
               
               
                   
                   
               
               
                   
                 Ctrl 
                 Rhap beads 
                 AbSeq PCR1; 
               
               
                   
                   
                   
                 Human Immune 
               
               
                   
                   
                   
                 Response N1 
               
               
                   
                 Sup A 
                 Supernatant 
                 AbSeq PCR1 
               
               
                   
                   
                 from denatured 
                   
               
               
                   
                   
                 Rhap bead 
                   
               
               
                   
                 OnBead A 
                 Denatured 
                 AbSeq PCR1; 
               
               
                   
                   
                 Rhap bead 
                 Human Immune 
               
               
                   
                   
                   
                 Response N1 
               
               
                   
                 Sup B 
                 Supernatant 
                 AbSeq PCR1 
               
               
                   
                   
                 from denatured 
                   
               
               
                   
                   
                 Rhap bead 
                   
               
               
                   
                 OnBead B 
                 Denatured 
                 Human Immune 
               
               
                   
                   
                 Rhap bead 
                 Response N1 
               
               
                   
                   
               
            
           
         
       
     
       FIGS.  32 A- 32 D  depict proxy oligo detection correlation analysis of Ctrl versus SupA ( FIG.  32 A ), Ctrl versus OnBeadA ( FIG.  32 B ), Ctrl versus SupB ( FIG.  32 C ), and SupA versus SupB ( FIG.  32 D ). Clustering was based on proxy oligo counts only. Table 25 depicts experimental conditions tested. 
     Table 25 and  FIGS.  33 A- 33 G  depict noise gating (cell signal to non-cell noise) analysis of the data provided herein. Noise gating analysis is depicted for conditions Ctrl ( FIG.  33 A ), OnBeadA ( FIG.  33 B ), SupA ( FIG.  33 C ), and SupB ( FIG.  33 D ). Cell labels per gate (relative to Ctrl) and protein labels per gate (relative to Ctrl) are shown in  FIGS.  33 E and  33 F , respectively.  FIG.  33 G  depicts a non-limiting exemplary noise gating of the combined data. 
     
       
         
           
               
             
               
                 TABLE 25 
               
             
            
               
                   
               
               
                 NOISE GATING 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Ctrl 
                 OnBeadA 
                 SupA 
                 SupB 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Total_Cell_Label 
                 655,921 
                 617,007 
                 680,231 
                 671,305 
               
               
                 C_Cell_Label 
                 507 
                 526 
                 526 
                 506 
               
               
                 D_Cell_Label 
                 17 
                 9 
                 7 
                 16 
               
               
                 B_Cell_Label 
                 546 
                 850 
                 574 
                 514 
               
               
                 A_Cell_Label 
                 654,851 
                 615,622 
                 679,124 
                 670,269 
               
               
                 Agg_Cell_Label 
                 0 
                 0 
                 0 
                 0 
               
               
                   
               
            
           
         
       
     
       FIGS.  34 A- 34 J  depict the results of mRNA sensitivity analysis.  FIG.  34 A  depicts a heat map of the top 25% of genes detected in the panel. Clustering and correlation analysis of the Ctrl versus OnBeadA ( FIGS.  34 B- 34 D ), Ctrl versus OnBeadB ( FIGS.  34 E- 34 G ), and OnBeadA versus OnBeadB ( FIGS.  34 E- 34 G ) conditions are shown. Clustering was based on mRNA counts only.  FIGS.  35 A- 35 D  depict analysis of noise per oligo in different gates for the conditions Ctrl ( FIG.  35 A ), SupA ( FIG.  35 B ), SupB ( FIG.  35 C ), and On Bead ( FIG.  35 D ). Total reads per oligo followed input ratios in different gates.  FIG.  36    depicts a Cell Label comparison B versus cell gate. Over 90% B gate cell labels in all 4 sample pairs with a C-gate cell label with 1 cell label difference and only approximately 15% randomly generated cell labels pairs with a C-gate cell label with 1 cell label difference. 
     Proxy oligos denatured off of Rhapsody beads were found to be amplified as robustly as standard conditions. The results shown that the reverse transcriptase transcribes the bead capture oligo onto the 3′ end of proxy oligos—and therefor can be feasible option to pursue to fix unwanted product generation. In some embodiments, PCR on beads (on proxy oligo cDNA) was not as efficient as PCR on soluble oligo proxies, unless denaturation prior to PCR1 negatively impacted Rhapsody beads. Oligo proxies are in higher concentration than Ab-oligos in cell based experiments and/or oligo proxies are more readily reverse transcribed. It was observed that the same amount of sequencing for cell based experiments typically yields higher saturation. Not much unwanted products were generated, despite “low” cell input. Finally, it was found that denaturation of beads can alter mRNA detection. A 10% decrease in signal in test conditions vs. control was observed. A much greater detection of the genes ELANE, JUNB, CSTD was observed. No trends in the primer features for these targets were observed. These results demonstrate that the methods and compositions provided herein can be employed for separate PCR workflows for protein quantitation and RNA quantitation. 
     Terminology 
     In at least some of the previously described embodiments, one or more elements used in an embodiment can interchangeably be used in another embodiment unless such a replacement is not technically feasible. It will be appreciated by those skilled in the art that various other omissions, additions and modifications may be made to the methods and structures described above without departing from the scope of the claimed subject matter. All such modifications and changes are intended to fall within the scope of the subject matter, as defined by the appended claims. 
     With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Any reference to “or” herein is intended to encompass “and/or” unless otherwise stated. 
     It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. 
     As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like include the number recited and refer to ranges which can be subsequently broken down into sub-ranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 articles refers to groups having 1, 2, or 3 articles. Similarly, a group having 1-5 articles refers to groups having 1, 2, 3, 4, or 5 articles, and so forth. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.