# Patent

## Title
Methods for producing ligand arrays

## Abstract

Methods for producing ligand arrays, e.g., peptide and nucleic acid arrays, as well as the arrays produced thereby, methods for use of the arrays and kits that include the same are provided. In one embodiment of the subject methods, a substrate having a surface displaying acetate functional groups that produce surface bound hydroxyl functional groups upon hydrolysis is first provided, where the acetate groups are then hydrolyzed to hydroxyl functional groups. In another embodiment of the subject methods, a substrate having a surface displaying alkenyl functional groups is first provided, where the alkenyl functional groups are then converted to carboxylic functional groups. The resultant substrates, optionally after an additional functionalization step, are then contacted with ligands, e.g., via deposition of each different ligand onto a different region of the surface, resulting in covalent attachment of the contacted ligands to the surface. The subject methods find use in the preparation of a variety of different types of arrays, where the produced arrays find use in a variety of different applications, including both genomic and proteomic applications.

## Background
TECHNICAL FIELD
The field of this invention is ligand arrays, including protein and nucleic acid arrays.
BACKGROUND OF THE INVENTION
Arrays of binding agents (ligands), such as nucleic acids and polypeptides, have become an increasingly important tool in the biotechnology industry and related fields. These binding agent or ligand arrays, in which a plurality of binding agents are positioned on a solid support surface in the form of an array or pattern, find use in a variety of applications, including gene expression analysis, drug screening, nucleic acid sequencing, mutation analysis, and the like.
A feature of many arrays that have been developed is that each of the polymeric compounds of the array is stably attached to a discrete location on the array surface, such that its position remains constant and known throughout the use of the array. Stable attachment is achieved in a number of different ways, including covalent bonding of the polymer to the support surface and non-covalent interaction of the polymer with the surface.
Where the ligands of the arrays are polymeric, e.g. as is the case with nucleic acid and polypeptide arrays, there are two main ways of producing such arrays, i.e., via in-situ synthesis in which the polymeric ligand is grown on the surface of the substrate in a step-wise fashion and via deposition of the full ligand, e.g., a presynthesized nucleic acid/polypeptide, cDNA fragment, etc., onto the surface of the array. In many situations where the desired polymeric ligands are long, the latter protocol of depositing full ligands on the substrate surface is desirable.
A number of different protocols have been developed in which full ligands are deposited onto the surface of an array, where such methods include those in which polylysine is adsorbed onto the surface of a glass support, those in which the surface of a glass support is modified via silylation to display various functional groups, and the like.
However, there is continued interest in the development of new protocols for producing arrays via deposition of full ligands onto the surface of the array.
Relevant Literature
U.S. Patents of interest include: U.S. Pat. Nos. 6,319,674, 6,258,454, 6,387,631B1 and references cited therein. Also of interest are Pomerantz et al., Thin Solid Films (1985) 132: 153–162; and Sudholter et al, Langmuir (1998) 14: 1759 to 1768
SUMMARY OF THE INVENTION
Methods for producing ligand arrays, e.g., peptide and nucleic acid arrays, as well as the arrays produced thereby, methods for use of the arrays and kits that include the same are provided. In one embodiment of the subject methods, a substrate having a surface displaying acetate functional groups that produce surface bound hydroxyl functional groups upon hydrolysis is first provided, where the acetate groups are then hydrolyzed to hydroxyl functional groups. In another embodiment of the subject methods, a substrate having a surface displaying alkenyl functional groups is first provided, where the alkenyl functional groups are then converted to carboxylic functional groups. The resultant substrates, optionally after an additional functionalization steps, are then contacted with ligands, e.g., via deposition of each different ligand onto a different region of the surface, resulting in covalent attachment of the contacted ligands to the surface. The subject methods find use in the preparation of a variety of different types of arrays, where the produced arrays find use in a variety of different applications, including both genomic and proteomic applications.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 provides a schematic of a surface modification method according to a first embodiment of the subject invention.
FIG. 2 provides a schematic of a surface modification method according to a second embodiment of the subject invention.



DEFINITIONS
The term “polymer” means any compound that is made up of two or more monomeric units covalently bonded to each other, where the monomeric units may be the same or different, such that the polymer may be a homopolymer or a heteropolymer. Representative polymers include peptides, polysaccharides, nucleic acids and the like, where the polymers may be naturally occurring or synthetic.
The term “peptide” as used herein refers to any polymer compound produced by amide formation between a α-carboxyl group of one amino acid and an α-amino group of another group.
The term “oligopeptide” as used herein refers to peptides with fewer than about 10 to 20 residues, i.e. amino acid monomeric units.
The term “polypeptide” as used herein refers to peptides with more than 10 to 20 residues.
The term “protein” as used herein refers to polypeptides of specific sequence of more than about 50 residues.
The term “nucleic acid” as used herein means a polymer composed of nucleotides, e.g. deoxyribonucleotides or ribonucleotides, or compounds produced synthetically (e.g. PNA as described in U.S. Pat. No. 5,948,902 and the references cited therein) which can hybridize with naturally occurring nucleic acids in a sequence specific manner analogous to that of two naturally occurring nucleic acids, e.g., can participate in Watson-Crick base pairing interactions.
The terms “ribonucleic acid” and “RNA” as used herein mean a polymer composed of ribonucleotides.
The terms “deoxyribonucleic acid” and “DNA” as used herein mean a polymer composed of deoxyribonucleotides.
The term “oligonucleotide” as used herein denotes single stranded nucleotide multimers of from about 10 to 100 nucleotides and up to 200 nucleotides in length.
The term “polynucleotide” as used herein refers to single or double stranded polymer composed of nucleotide monomers of generally greater than 100 nucleotides in length.
The term “functionalization” as used herein relates to modification of a solid substrate to provide a plurality of functional groups on the substrate surface. By a “functionalized surface” as used herein is meant a substrate surface that has been modified so that a plurality of functional groups are present thereon.
The term “array” encompasses the term “microarray” and refers to an ordered array presented for binding to ligands such as polymers, polynucleotides, peptide nucleic acids and the like.
The terms “reactive site”, “reactive functional group” or “reactive group” refer to moieties on a monomer, polymer or substrate surface that may be used as the starting point in a synthetic organic process. This is contrasted to “inert” hydrophilic groups that could also be present on a substrate surface, e.g., hydrophilic sites associated with polyethylene glycol, a polyamide or the like.
The term “oligomer” is used herein to indicate a chemical entity that contains a plurality of monomers. As used herein, the terms “oligomer” and “polymer” are used interchangeably, as it is generally, although not necessarily, smaller “polymers” that are prepared using the functionalized substrates of the invention, particularly in conjunction with combinatorial chemistry techniques. Examples of oligomers and polymers include polydeoxyribonucleotides (DNA), polyribonucleotides (RNA), other polynucleotides which are C-glycosides of a purine or pyrimidine base, polypeptides (proteins), polysaccharides (starches, or polysugars), and other chemical entities that contain repeating units of like chemical structure. In the practice of the instant invention, oligomers will generally comprise about 2–50 monomers, preferably about 2–20, more preferably about 3–10 monomers.
The term “ligand” as used herein refers to a moiety that is capable of covalently or otherwise chemically binding a compound of interest. The arrays of solid-supported ligands produced by the methods can be used in screening or separation processes, or the like, to bind a component of interest in a sample. The term “ligand” in the context of the invention may or may not be an “oligomer” as defined above. However, the term “ligand” as used herein may also refer to a compound that is “pre-synthesized” or obtained commercially, and then attached to the substrate.
The term “sample” as used herein relates to a material or mixture of materials, typically, although not necessarily, in fluid form, containing one or more components of interest.
The terms “nucleoside” and “nucleotide” are intended to include those moieties which contain not only the known purine and pyrimidine bases, but also other heterocyclic bases that have been modified. Such modifications include methylated purines or pyrimidines, acylated purines or pyrimidines, alkylated riboses or other heterocycles. In addition, the terms “nucleoside” and “nucleotide” include those moieties that contain not only conventional ribose and deoxyribose sugars, but other sugars as well. Modified nucleosides or nucleotides also include modifications on the sugar moiety, e.g., wherein one or more of the hydroxyl groups are replaced with halogen atoms or aliphatic groups, or are functionalized as ethers, amines, or the like.
As used herein, the term “amino acid” is intended to include not only the L-, D- and nonchiral forms of naturally occurring amino acids (alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, valine), but also modified amino acids, amino acid analogs, and other chemical compounds which can be incorporated in conventional oligopeptide synthesis, e.g., 4-nitrophenylalanine, isoglutamic acid, isoglutamine, ε-nicotinoyl-lysine, isonipecotic acid, tetrahydroisoquinoleic acid, α-aminoisobutyric acid, sarcosine, citrulline, cysteic acid; t-butylglycine, t-butylalanine, phenylglycine, cyclohexylalanine, β-alanine, 4-aminobutyric acid, and the like.
The term “acetate” as used herein refers to the acetato group, in many embodiments of the formula: O—(CO)—R′, where R′′ may be any group that does not unacceptably interfere with the acid hydrolysis of the functional group to produce a hydroxyl group. In some embodiments, the acetate functional group has the formula:

—O(CO)CR1R2R3;

wherein:

R1, R2, and R3 may be the same or different and are independently H or chosen from a number of substituents, including but not limited to: halogen, alkyoxy, aryloxy, alkyl, aryl, heteroalkyl, heteroaryl, etc.
The term “alkyl” as used herein refers to substituted or unsubstituted, cyclic, or linear, branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, octyl, decyl, tetradecyl, hexadecyl, eicosyl, tetracosyl and the like, 3-methyl-octyl, 3-methoxyoctyl, 3-chloro-octyl and the like, as well as cycloalkyl groups such as cyclopentyl, cyclohexyl and the like.
The term “alkenyl” as used herein refers to substituted or unsubstituted, cyclic, or linear, branched or unbranched unsaturated hydrocarbon group of 1 to 24 carbon atoms. Examples include octenyl, nonenyl, decenyl, undecenyl and the like, isopropenyl, isobutenyl, isopentenyl, octenyl, isoprenyl and the like.
The term “alkoxy” as used herein refers to a substituent —O—R wherein R is alkyl as defined above. Examples of alkoxy groups include methoxy, ethoxy, n-propoxy, isopropoxy, sec-butoxy, tert-butoxy and the like.
The terms “halogen” or “halo” are used to refer to a chloro, bromo, fluoro or iodo substituent, or combinations thereof, such as dichloro, chlorobromo, dichlorobromo and the like.
A “silane” or “silanizing reagent” refers to a compound or reagent in which a central silicon atom is bonded to four substituents, wherein the substituents may be the same or different.
The term “protecting group” refers to chemical moieties that, while stable to the reaction conditions, mask or prevent a reactive group from participating in a chemical reaction. Protecting groups may also alter the physical properties such as the solubility of compounds, so as to enable the compounds to participate in a chemical reaction. Examples of protecting groups are known in the art, for example, Greene et al., Protective Groups in Organic Synthesis, 2nd Ed., New York: John Wiley & Sons, 1991.
“Optional” or “optionally” means that the subsequently described circumstance may or may not occur, so that the description includes instances where the circumstance occurs and instances where it does not. For example, the phrase “optionally substituted” means that a non-hydrogen substituent may or may not be present, and, thus, the description includes structures wherein a non-hydrogen substituent is present and structures wherein a non-hydrogen substituent is not present.
“Hydrolysis” means a reaction generated by contact with water, or an aqueous solution of an acid or alkali, where the reaction results in a bond cleavage and displacement by the nucleophiles in water or in the aqueous solution. In embodiments of the invention, an acetate group may be subjected to hydrolysis, i.e., hydrolyzed, to produce a hydroxyl group.
An “array,” includes any two-dimensional or substantially two-dimensional (as well as a three-dimensional) arrangement of addressable regions bearing a particular chemical moiety or moieties (e.g., biopolymers such as polynucleotide or oligonucleotide sequences (nucleic acids), polypeptides (e.g., proteins), carbohydrates, lipids, etc.) associated with that region. In the broadest sense, the preferred arrays are arrays of polymeric binding agents, where the polymeric binding agents may be any of: polypeptides, proteins, nucleic acids, polysaccharides, synthetic mimetics of such biopolymeric binding agents, etc. In many embodiments of interest, the arrays are arrays of nucleic acids, including oligonucleotides, polynucleotides, cDNAs, mRNAs, synthetic mimetics thereof, and the like. Where the arrays are arrays of nucleic acids, the nucleic acids may be covalently attached to the arrays at any point along the nucleic acid chain, but are generally attached at one of their termini (e.g. the 3′ or 5′ terminus). Sometimes, the arrays are arrays of polypeptides, e.g., proteins or fragments thereof.
Any given substrate may carry one, two, four or more or more arrays disposed on a front surface of the substrate. Depending upon the use, any or all of the arrays may be the same or different from one another and each may contain multiple spots or features. A typical array may contain more than ten, more than one hundred, more than one thousand more ten thousand features, or even more than one hundred thousand features, in an area of less than 20 cm2 or even less than 10 cm2. For example, features may have widths (that is, diameter, for a round spot) in the range from a 10 μm to 1.0 cm. In other embodiments each feature may have a width in the range of 1.0 μm to 1.0 mm, usually 5.0 μm to 500 μm, and more usually 10 μm to 200 μm. Non-round features may have area ranges equivalent to that of circular features with the foregoing width (diameter) ranges. At least some, or all, of the features are-of different compositions (for example, when any repeats of each feature composition are excluded the remaining features may account for at least 5%, 10%, or 20% of the total number of features). Interfeature areas will typically (but not essentially) be present which do not carry any polynucleotide (or other biopolymer or chemical moiety of a type of which the features are composed). Such interfeature areas typically will be present where the arrays are formed by processes involving drop deposition of reagents but may not be present when, for example, photolithographic array fabrication processes are used. It will be appreciated though, that the interfeature areas, when present, could be of various sizes and configurations.
Each array may cover an area of less than 100 cm2, or even less than 50 cm2, 10 cm2 or 1 cm2. In many embodiments, the substrate carrying the one or more arrays will be shaped generally as a rectangular solid (although other shapes are possible), having a length of more than 4 mm and less than 1 m, usually more than 4 mm and less than 600 mm, more usually less than 400 mm; a width of more than 4 mm and less than 1 m, usually less than 500 mm and more usually less than 400 mm; and a thickness of more than 0.01 mm and less than 5.0 mm, usually more than 0.1 mm and less than 2 mm and more usually more than 0.2 and less than 1 mm. With arrays that are read by detecting fluorescence, the substrate may be of a material that emits low fluorescence upon illumination with the excitation light. Additionally in this situation, the substrate may be relatively transparent to reduce the absorption of the incident illuminating laser light and subsequent heating if the focused laser beam travels too slowly over a region. For example, substrate 10 may transmit at least 20%, or 50% (or even at least 70%, 90%, or 95%), of the illuminating light incident on the front as may be measured across the entire integrated spectrum of such illuminating light or alternatively at 532 nm or 633 nm.
Arrays can be fabricated using drop deposition from pulse jets of either polynucleotide precursor units (such as monomers) in the case of in situ fabrication, or the previously obtained polynucleotide. Such methods are described in detail in, for example, the previously cited references including U.S. Pat. No. 6,242,266, U.S. Pat. No. 6,232,072, U.S. Pat. No. 6,180,351, U.S. Pat. No. 6,171,797, U.S. Pat. No. 6,323,043, U.S. patent application Ser. No. 09/302,898 filed Apr. 30, 1999 by Caren et al., and the references cited therein. As already mentioned, these references are incorporated herein by reference. Other drop deposition methods can be used for fabrication, as previously described herein. Also, instead of drop deposition methods, photolithographic array fabrication methods may be used such as described in U.S. Pat. No. 5,599,695, U.S. Pat. No. 5,753,788, and U.S. Pat. No. 6,329,143. Interfeature areas need not be present particularly when the arrays are made by photolithographic methods as described in those patents.
An array is “addressable” when it has multiple regions of different moieties (e.g., different polynucleotide sequences) such that a region (i.e., a “feature” or “spot” of the array) at a particular predetermined location (i.e., an “address”) on the array will detect a particular target or class of targets (although a feature may incidentally detect non-targets of that feature). Array features are typically, but need not be, separated by intervening spaces. In the case of an array, the “target” will be referenced as a moiety in a mobile phase (typically fluid), to be detected by probes (“target probes”) which are bound to the substrate at the various regions. However, either of the “target” or “target probe” may be the one which is to be evaluated by the other (thus, either one could be an unknown mixture of polynucleotides to be evaluated by binding with the other). A “scan region” refers to a contiguous (preferably, rectangular) area in which the array spots or features of interest, as defined above, are found. The scan region is that portion of the total area illuminated from which the resulting fluorescence is detected and recorded. For the purposes of this invention, the scan region includes the entire area of the slide scanned in each pass of the lens, between the first feature of interest, and the last feature of interest, even if there exist intervening areas which lack features of interest. An “array layout” refers to one or more characteristics of the features, such as feature positioning on the substrate, one or more feature dimensions, and an indication of a moiety at a given location. “Hybridizing” and “binding”, with respect to polynucleotides, are used interchangeably.
By “remote location,” it is meant a location other than the location at which the array is present and hybridization occurs. For example, a remote location could be another location (e.g., office, lab, etc.) in the same city, another location in a different city, another location in a different state, another location in a different country, etc. As such, when one item is indicated as being “remote” from another, what is meant is that the two items are at least in different rooms or different buildings, and may be at least one mile, ten miles, or at least one hundred miles apart. “Communicating” information references transmitting the data representing that information as electrical signals over a suitable communication channel (e.g., a private or public network). “Forwarding” an item refers to any means of getting that item from one location to the next, whether by physically transporting that item or otherwise (where that is possible) and includes, at least in the case of data, physically transporting a medium carrying the data or communicating the data. An array “package” may be the array plus only a substrate on which the array is deposited, although the package may include other features (such as a housing with a chamber). A “chamber” references an enclosed volume (although a chamber may be accessible through one or more ports). It will also be appreciated that throughout the present application, that words such as “top,” “upper,” and “lower” are used in a relative sense only.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
Methods for producing ligand arrays, e.g., peptide and nucleic acid arrays, as well as the arrays produced thereby, methods for use of the arrays and kits that include the same are provided. In one embodiment of the subject methods, a substrate having a surface displaying acetate functional groups that produce surface bound hydroxyl functional groups upon hydrolysis is first provided, where the acetate groups are then hydrolyzed to hydroxyl functional groups. In another embodiment of the subject methods, a substrate having a surface displaying alkenyl functional groups is first provided, where the alkenyl functional groups are then converted to carboxylic functional groups. The resultant substrates, optionally after an additional functionalization steps, are then contacted with ligands, e.g., via deposition of each different ligand onto a different region of the surface, resulting in covalent attachment of the contacted ligands to the surface. The subject methods find use in the preparation of a variety of different types of arrays, where the produced arrays find use in a variety of different applications, including both genomic and proteomic applications.
Before the invention is described further, it is to be understood that the invention is not limited to the particular embodiments of the invention described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.
In this specification and the appended claims, the singular forms “a,” “an” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also encompassed within the invention, to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices and materials are now described.
All publications mentioned herein are incorporated herein by reference for the purpose of describing and disclosing the invention components which are described in the publications which might be used in connection with the presently described invention.
Methods
As summarized above, the invention provides methods for producing an array of at least two different ligands covalently bonded to a surface of a substrate. In one embodiment, the subject methods comprise providing a substrate having a surface displaying acetate functional groups, while in another embodiment the methods provide a substrate displaying alkenyl functional groups. The acetato and alkenyl functional groups of the provided surface functionalized substrates are then converted to hydroxyl and carboxylic functional groups, respectively. Following this conversion step, (and optionally a further functionalization step) the substrate surface is contacted with ligands resulting in covalent linkage of the ligands to the surface so as to produce a ligand array. Each of these steps is now described in greater detail below.
Substrates
In the subject methods, the surface of a solid substrate is first contacted with a derivatizing composition that contains one or more types of silanes, where in one embodiment, the surface is contacted with an acetate-functionalized silane, where the silane comprises a single type of silanizing agent. In another embodiment, the surface is contacted with a mixture of at least two different silanes, one of which is an alkenyl silane. The surface of the solid substrate is contacted with the one or more silanes under reaction conditions effective to couple the silanes to the substrate surface via reactive hydrophilic moieties present on the substrate surface. The reactive hydrophilic moieties on the substrate surface include substituted or unsubstituted hydroxyl, carboxyl, aldehyde, thiol, amino groups or combinations of hydrophilic moieties, or hydrophilic groups masked by a protecting group that may be removed to provide reactive hydrophilic moieties.
The substrate may comprise any material that has a plurality of reactive hydrophilic sites on its surface, or that can be treated or coated so as to have a plurality of such sites on its surface. Suitable materials include, but are not limited to, glass (particularly controlled pore glass, or “CPG”), quartz, silicon or silicon covered with silicon dioxide, ceramics, supports typically used for solid phase chemical synthesis, e.g., cross-linked polymeric materials (e.g., divinylbenzene styrene-based polymers), agarose (e.g. SEPHAROSETM), dextran (e.g., SEPHADEXTM), cellulosic polymers, polyacrylamides, and the like. The supports may be obtained commercially and used as is, or they may be treated or coated prior to functionalization. The substrate surfaces are typically planar, although planarity is not required and the surfaces can be of any geometry suitable for contact with silanizing reagents used in formation of an array.
In some embodiments, the substrate surface is “cleaned/primed” prior to contact with the silanizing reagent of one or more silane(s). In certain of these embodiments, the surfaces may be placed in contact with a solvent prior to contact with the silanizing reagents. The solvent, prepared prior to contact with the surfaces, may be generated by dissolution of a small amount of water in a hydrophobic solvent, such as toluene, benzene and the like. The surfaces may be first placed in contact with the solvent, followed by the addition of the silanizing reagents.
The substrate surfaces are derivatised by contact with silanizing reagents to produce functionalized surfaces. A variety of silanizing reagents may be used. It is known in the art of silane chemistry that substituents that are facile leaving groups on the silane facilitate binding of the silane to hydrophilic moieties on substrate surfaces are of interest. Examples of leaving group substituents on the silane include, but are not limited to: halogens, alkoxy, aryloxy moieties, and the like. Hydrophilic moieties, for example hydroxyl groups, react with silanes, displacing the leaving group on the silane to form a siloxy bond to the substrate surface. The silanizing reagents are contacted with the surface of the substrate in the presence of a sufficient amount of water to provide for the silylation reaction, e.g., from about 100 to about 300 μg/ml.
The subject methods may be employed to produce a variety of functionalized surfaces for use in polymer arrays, depending on the silanizing reagent used and the derivation chemistry, as described in more detail below. In one embodiment of the subject methods, acetate functionalized substrate surfaces are provided in a first step. In another embodiment, modified carboxylic acid substrate surfaces are provided in the first step.
Preparation of Functionalized Acetate Substrate Surfaces
In these embodiments, the derivatizing composition contains a single type of silane, where the silane includes an acetate hydrolyzable functional group, e.g., acid or alkali hydrolyzable functional group, that produces a hydroxyl functional group upon exposure to hydrolysis conditions, e.g., either acid or alkali hydrolysis conditions, as described in greater detail below. The derivatizing composition comprises a single type of silanizing reagent, the reagent comprising typically of a silyl and an acetate terminal group separated by a linker, where the linker is often a carbon chain from about 6 to about 20, often from about 8 to about 18 carbon atoms in length. In certain embodiments, the silanizing reagent is represented by the formula:

Ac-(L)n—Si(RLRxRy)

In the above formula, the RL, which may be the same or different, are leaving groups, the Rx and Ry, which may be the same or different, are either lower alkyl or leaving groups like RL. More specifically, the RL moieties, which are leaving groups, are such that they enable binding of the silanes to the surface. Typically, the leaving groups are hydrolyzable so as to form a siloxy linkage to surface hydroxyl groups. Examples of suitable leaving groups include, but are not limited to, halogen atoms, particularly chloro, and alkoxy moieties, particularly lower alkoxy moieties. The Rx and Ry are either lower alkyl, e.g., methyl, ethyl, isopropyl, n-propyl, 1-butyl, or the like, or leaving groups as just described with respect to RL. Thus, each type of silane will generally contain a, trichlorosilyl functionality, a trialkoxysilyl functionality wherein the alkoxysilyl is a lower alkoxysilyl group such as trimethoxysilyl, mixed functionalities such as diisopropylchlorosilyl, dimethylchlorosilyl, ethyldichlorosilyl, methylethylchlorosilyl or the like.
Reaction of the substrate surface with the derivatizing composition is carried out under reaction conditions effective to couple the silane(s) to the surface hydrophilic moieties and thereby provide —Si-(L)n-Ac groups on the substrate surface. The silane, upon coupling, provides surface —Si-(L)n-Ac groups, where Ac is the acetate functionality.
Ac is any hydrolyzable acetate functional group that produces a hydroxyl function group (—OH) upon exposure to either acid or alkali hydrolysis conditions, i.e., Ac is any acid or alkali hydrolyzable acetate group. In many embodiments, the acid or alkali hydrolyzable acetate functional group is a group that yields a free carboxylic acid upon hydrolysis and the desired surface bound hydroxyl moiety.
In many of the above embodiments, Ac has the following formula: O—(CO)—R′, where R′ is, in many embodiments, an alkyl group as defined above. However, R′ may be any group that does not unacceptably interfere with the acid hydrolysis of the functional group to produce a hydroxyl group, as described in greater detail below. In some embodiments, the acetate functional group has the formula:

—O(CO)CR1R2R3;

wherein:

    
    
        R1, R2, and R3 are independently chosen from H and halogen, alkyoxy, aryloxy, alkyl, aryl, heteroalkyl, heteroaryl.
    
    


L represents a linker and n is 0 or 1, such that a linker may or may not be present. If a linker is present, it will generally be a C1–C24 hydrocarbon linking group. In one embodiment, L is C1–C24 alkyl, including C8–C18 alkyl, such as C10–C18 alkyl.
Conversion of Acetate Functional Groups to Hydroxyl Functional Groups
The next step in the subject methods is to convert the hydrolyzable functional groups on the substrate surface as described above to hydroxyl functional groups. The hydrolyzable functional groups are converted to hydroxyl functional groups using any convenient protocol. Both acid and alkali hydrolysis protocols find use in the subject invention.
In certain embodiments, acid hydrolysis is employed to convert the hydrolyzable groups to hydroxyl groups. In these embodiments, the substrate surface is subjected to acid hydrolysis conditions that convert the acid hydrolyzable functional groups to hydroxyl functional groups. To subject the substrate surface to acid hydrolysis conditions, the substrate surface is typically contacted with an acidic aqueous fluid under conditions and for a period of time sufficient to cause acid hydrolysis. Contact may be achieved using any convenient protocol, e.g., dispensing the acid solution onto the surface of the substrate, submersing the substrate in the aqueous fluid, flowing a volume of the aqueous fluid across the substrate surface, etc. Contact is carried out under appropriate conditions, e.g., at a temperature ranging from about room temperature to about 100° C., usually from about 40 to about 60° C., for a period of time ranging from about 10 minutes to about 6 hours, typically from about 1 hour to about 2 hours. By acid solution is meant a solution having a pH of less than about 7, typically about 1. The solution may include one or more different acids or derivatives thereof. Suitable acids that lack a hydrocarbon moiety, e.g., mineral acids, include halogen acids, oxy acids and mixtures thereof, where specific acids of interest of this type include, but are not limited to, hydrochloric, nitric, sulfuric, phosphoric, hydroboric, hydrobromic, carbonic and hydroiodic acids. For such acids, the acid can be a concentrated acid, or can be diluted. Also of interest are acids that include a hydrocarbon moiety, e.g., organic acids, where such acids include, but are not limited to, any organic acid of one to six (C1 to C6) carbons in length. Organic acids of this type include, but are not limited to, formic, acetic, propionic, maleic, butanoic, valeric, hexanoic, phenolic, cyclopentanecarboxylic, benzoic, methane sulfinic, and the like. For an organic acid, the acid can be in concentrated form, or can be diluted. The acidic treatment solution can be composed of either a monobasic or a polybasic acid. Acids are “monobasic” when they have only one replaceable hydrogen atom and yield only one series of salts (e.g., HCl). Acids are “polybasic” when they contain two or more hydrogen atoms that may be neutralized by alkalis and replaced by organic radicals.
In other embodiments, hydrolysis of the hydrolyzable functional group is achieved by alkali hydrolysis, i.e., use of alkali hydrolysis conditions. To subject the substrate surface to alkali hydrolysis conditions, the substrate surface is typically contacted with an alkali fluid under conditions and for a period of time sufficient to cause alkali hydrolysis. Contact is carried out under appropriate conditions, e.g. at a temperature ranging from about room temperature to 100° C., usually from about room temperature to 50° C., usually from about 5 minutes to about 2 hours, typically from about 5 minutes to 30 minutes. By alkali solution is meant a solution having a pH greater than 7. The solution may include one or more different alkalis or derivatives thereof. Suitable alkalis include, for instance, sodium hydroxide, potassium hydroxide, etc., dissolved in water or the formation of the corresponding alkoxide by dissolution of the hydroxide in an alcohol such as methanol, ethanol etc. The alkali is dissolved in the solvent with a % wt of between 1 to 50%, preferably between 1 to 10%. The preferred solvent is an alcohol, either methanol or ethanol of any organic alcohol or mixture of one or more alcohols. Whereas it is well known that water based alkali solutions of, for instance, sodium hydroxide in water, destroy the siloxane surface (the point at which the silicon atom is attached to the substrate via an oxygen atom) quite easily (in less than an hour) this is not the case for alcohol based alkalis. Indeed the surface is stable to such solvents for long periods of time (at least greater than 3 days, if not more). As such, the alkali hydrolysis conditions employed are generally alcohol based alkali conditions.
The above hydrolysis protocols result in conversion of the hydrolyzable functional groups to hydroxyl groups. While the particular results achieved may vary, the percentage of initial hydrolyzable functional groups that are converted is, in many embodiments, at least about 5%, usually at least about 10% and more usually at least about 20 number % of the initial number of hydrolyzable functional groups, where the number % may be higher, e.g., 30, 40, 50, 60, 70, 80, 90, 95, 99. The resultant hydroxyl group functionalized surface may be used immediately for covalent ligand attachment or, where desired, further functionalized prior to ligand attachment. For example, in many embodiments the ligand to be covalently attached to the surface may be functionalized with a hydroxyl functional group, which provides for covalent attachment of the ligand to the substrate surface via reaction of the ligand functional group with the surface hydroxyl functional group.
Alternatively, the hydroxyl functional group may be converted to a number of different types of functional groups which are reactive to the ligand of interest, i.e., ligand reactive functional groups. By ligand reactive functional groups is meant groups that react with moieties present on the target ligands, (i.e., the ligands to be deposited onto the surface and covalently bound thereto) in manner that produces a covalent bond or linkage between the ligand and the substrate surface. The hydroxyl functional groups may be converted to a variety of different types of reactive moieties using a variety of different protocols, depending on the particular nature of the ligand that is to be covalently bound to the substrate surface. Representative ligand reactive functional groups to which the, initial hydroxyl functional groups may be converted include: aldehyes, amines, and the like. The particular ligand reactive functional group to which the initial hydroxyl group is converted will be chosen, at least in part, on considerations that include, but are not limited to: the nature of the ligand and functional groups that may be present thereon, ease of conversion, and the like.
The particular conversion protocol employed will vary with respect to the nature of the desired ligand reactive functional group, and may or may not involve the production of one or more intermediate groups. In one embodiment, the hydroxyl functional groups of the initial substrate surface are converted to aldehyde functional groups, e.g., via controlled oxidation to aldehyde functionalities, e.g., via Moffat oxidations, where primary alcohols are specifically and efficiently converted to the corresponding aldehydes under mild conditions. See e.g., Pftizner and Moffatt, Comp. Org Syn. 7, 291 (1991), J. Amer. Chem. Soc. (1965) 87:5670–78. In yet another embodiment, the surface hydroxyl groups are converted to amine reactive benzaldehyde functionalities using benzaldehyde phosphoramidites. More specifically, the hydroxyl moiety can be reacted with a benzaldehyde phosphoramidite, followed by acidic deprotection of the benzaldehyde moiety and basic deprotection of the phosphate moiety. Such protocols are known in the art, see e.g., WO 01/09385 and its priority application Ser. No. 09/364,320, the disclosure of latter of which is herein incorporated by reference.
Following production of the hydroxyl functional groups, and any subsequent functionalization of the hydroxyl groups, as described above, the resultant hydroxyl functionalized surface can be employed in the fabrication of arrays, e.g., via polymeric ligand deposition where one or more polymeric ligands are contacted with the functionalized surface; or in-situ polymeric ligand synthesis, as described immediately below in greater detail.
Preparation of Functionalized Carboxylic Acid Surfaces
In these embodiments, the derivatizing composition comprises at least one type of silane, where the silane includes an alkenyl functional group. In many embodiments, the derivatizing composition may include two types of silanes, a first silane that may be represented as R1—Si(RLRxRy) and a second silane having the formula: alkenyl group-(L)n—Si(RLRxRy). In these formulae, the RL, which may be the same or different, are leaving groups; the Rx and Ry, which may be the same or different, are either lower alkyl or leaving groups like RL. R1 is a chemically inert moiety that upon binding to the substrate surface lowers the surface energy thereof; n is 0 or 1, L is a linking group, and alkenyl group is the alkenyl functional group as summarized above and described in greater detail below. In those embodiments where the surface is contacted with only a single type of silane, the silane is the alkenyl, silane described above. Reaction of the substrate surface with the derivatizing composition is carried out under reaction conditions effective to couple the silane(s) to the surface hydrophilic moieties and thereby provide —Si—R1 groups and —Si-(L)n-alkenyl groups on the substrate surface.
More specifically, the RL moieties, which are leaving groups, are such that they enable binding of the silanes to the surface. Typically, the leaving groups are hydrolyzable so as to form a silanol linkage to surface hydroxyl groups. Examples of suitable leaving groups include, but are not limited to, halogen atoms, particularly chloro, and alkoxy moieties, particularly lower alkoxy moieties. The Rx and Ry are either lower alkyl, e.g., methyl, ethyl, isopropyl, n-propyl, t-butyl, or the like, or leaving groups as just described with respect to RL. Thus, each type of silane will generally contain a trichlorosilyl functionality, a tri(alkoxysilyl functionality, wherein the alkoxysilyl is a lower alkoxysilyl group such as trimethoxysilyl, mixed functionalities such as diisopropylchlorosilyl, dimethylchlorosilyl, ethyldichlorosilyl, methylethylchlorosilyl or the like.
In those embodiments where a mixture of silanes make up the derivatizing composition, the first silane is a derivatizing agent that reduces surface energy as desired, while the second silane provides the hydrolyzable functionality. Thus, with respect to the first silane, coupling to the substrate yields surface —Si—R1 groups as explained above, wherein R1 is a chemically inert moiety that upon binding to the substrate surface lowers surface energy. By “chemically inert” is meant that R1 will not be cleaved or modified when the functionalized substrate is used for its intended purpose, e.g., in solid phase chemical synthesis, hybridization assays, or the like. Typically, R1 is an alkyl group, generally although not necessarily containing in the range of 2 to 24 carbon atoms, preferably in the range of 10 to 18 carbon atoms.
The second silane, upon coupling, provides surface —Si-(L)n-alkenyl moiety groups, where R2 is the hydrolyzable functionality. Of course, if the Rx and Ry are not leaving groups, the surface moieties provided will actually be —SiRxRy-(L)n-alkenyl moiety groups, which applicants intend to encompass by the more generic representation —Si-(L)nalkenyl moiety.
The alkenyl moiety is any group that contains a carbon-carbon double bond that is accessible for modification, as described below, to produce a carboxylic functional group. The alkenyl moiety comprises a hydrocarbon chain that is often 2 to 10 carbon atoms in length, sometimes 2 to 6 carbon atoms in length, e.g., 2 to 4 carbon atoms in length, where the hydrocarbon chain includes at least one double bond, and often only a single double bone. The position of the double bond may vary such that it is in the middle of the chain or at a terminus thereof, but often it is at a terminus thereof, and more often at the terminus furthest away from the silyl group of the silanizing reagent.
L represents a linker and n is 0 or 1, such that a linker may or may not be present. If a linker is present, it will generally be a C1–C24 hydrocarbylene linnking group. Normally, L is C1–C24 alkylene, perferably C10–C18 alkylene.
The density of the alkenyl functional groups on the substrate surface, following reaction with the derivatizing composition, is determined by the relative proportions of the first and second silanes in the derivatizing composition. That is, a higher proportion of the second silane in the derivatizing composition will provide a greater density of alkenyl function groups, while a higher proportion of the first silane will give rise to a lower density of alkenyl groups. Optimally, the first silane is present in the range of approximately 0 wt. % to 99.5 wt. % of the derivatization composition, preferably in the range of approximately 20 wt. % to 90 wt. % of the composition, while the second silane correspondingly is present in the range of approximately 0.5 wt. % to 100 wt. % of the derivatization composition, preferably in the range of approximately 10% wt. % to 80 wt. % of the composition, where about a 1:1 ratio of first to second silanizing reagents is of interest in certain embodiments.
In many embodiments, the resultant surface of the functionalized substrates contain both —Si—R1 and Si-(L)n-alkenyl functional groups, present at a predetermined ratio, with the ratio determining both surface energy and density of functional groups. In other words, the functional surface of the substrate displays acid or alkali hydrolyzable functional groups. See also U.S. Pat. No. 6,258,454 for a further description of the general process of derivatizing a surface, the disclosure of which is herein incorporated by reference.
The resultant surfaces displaying an alkenyl functional group are then typically further derivatized to produce surfaces displaying carboxylic acid functional groups. The alkenyl groups may be converted to carboxylic acid groups, for example, by oxidation using the method of Whitesides et al (Langmuir, 1989, 5, 1074–1087), by transition metal oxidants (see for example, Carey and Sundberg, Advanced Organic Chemistry, Part B, Plenum Press, 1983, page 511 and references therein, or by other methods known in the art. The above step results in conversion of the alkenyl functional group to a carboxylic functional group. While the particular results achieved may vary, the percentage of initial alkenyl functional groups that are converted is, in many embodiments, at least about 5%, usually at least about 10% and more usually at least about 20 number % of the initial number of alkenyul functional groups, where the number % may be higher, e.g., 30, 40, 50, 60, 70, 80, 90, 95, 99. The resultant carboxylic functional group functionalized surface may be used immediately for covalent ligand attachment or, where desired, further functionalized prior to ligand attachment. For example, in many embodiments the ligand to be covalently attached to the surface may be functionalized with a carboxylic acid functional group, which provides for covalent attachment of the ligand to the substrate surface via reaction of the ligand functional group with the surface carboxylic functional group.
Alternatively, the carboxylic functional group may be converted to a number of different types of functional groups which are reactive to the ligand of interest, i.e., ligand reactive functional groups. By ligand reactive functional groups is meant groups that react with moieties present on the target ligands, (i.e., the ligands to be deposited onto the surface and covalently bound thereto) in manner that produces a covalent bond or linkage between the ligand and the substrate surface. The carboxylic functional groups may be converted to a variety of different types of reactive moieties using a variety of different protocols, depending on the particular nature of the ligand that is to be covalently bound to the substrate surface. Representative ligand reactive functional groups to which the initial hydroxyl functional groups may be converted include, but are not limited to: pyridine, benzimidazole, indole, imidazole, thiophene, isoquinoline, quinazoline and the like. The particular ligand reactive functional group to which the initial hydroxyl group is converted will be chosen, at least in part, on considerations that include, but are not limited to: the nature of the ligand and functional groups that may be present thereon, ease of conversion, and the like.
The particular conversion protocol employed will vary with respect to the nature of the desired ligand reactive functional group, and may or may not involve the production of one or more intermediate groups. In one embodiment, the hydroxyl groups on the carboxylic-group may be further derivatized by displacement of the hydroxyl group by a group selected from the group comprising pyridine, benzimidazole, indole, imidazole, thiophene, isoquinoline, quinazoline, aceto halide, e.g., acetyl chloride, etc. Suitable reagents comprising such nucleophiles for use, for example, 1,1′-carbonyldiimidazole, are known in the art.
Following production of the carboxyl functional groups, and any subsequent functionalization of the carboxyl groups, as described above, the resultant hydroxyl functionalized surface can be employed in the fabrication of arrays, e.g., via polymeric ligand deposition where one or more polymeric ligands are contacted with the functionalized surface; or in-situ polymeric ligand synthesis, as described immediately below in greater detail.
Features of the Functionalized Substrate Surfaces
A feature of the functionalized surfaces produced according to the subject invention is that they are particularly suitable for use as substrates in ligand array production. In particular, the contact angle of the subject functionalized surfaces is one that makes the surfaces suitable for use in array fabrication by fluid deposition of ligands, e.g., pulse-jet deposition. The contact angles of the subject functionalized surface substrates are typically at least about 45°, often at least about 50°, and sometimes at least about 60°, e.g., at least about 65°, at least about 70°, at least about 75°, at least about 80°, at least about 90%, at least about 99°, etc. Contact angles are static contact angle measurements as determined using the protocol described in the Experimental Section, below.
Polymeric Ligand Attachment in Array Fabrication
In many embodiments, the subject surfaces prepared as described above are employed in array facbrication where polymeric ligands are attached to the surface. In these embodiments, the ligands that are contacted with the substrate surface are typically polymeric binding agents. The polymeric binding agents may vary widely, where the only limitation is that the polymeric binding agents are made up of two more, usually a plurality of, monomeric units covalently attached in sequential order to one another such that the polymeric compound has a sequence of monomeric units. Typically, the polymeric binding agent includes at least 5 monomeric units, usually at least 10 monomeric units and more usually at least 15 monomeric units, where in many embodiments the number of monomeric units in the polymers may be as high as 5000 or higher, but generally will not exceed about 2000. In certain embodiments, the number of monomeric residues in the polymeric binding agent is at least about 50, usually at least about 100 and more usually at least about 150.
Polymeric binding agents of particular interest include biopolymeric molecules, such as polypeptides, nucleic acids, polysaccharides and the like, where polypeptides and nucleic acids, as well as synthetic mimetics thereof, are of particular interest in many embodiments.
In many embodiments, the polymeric binding agents are nucleic acids, including DNA, RNA, nucleic acids of one or more synthetic or non-naturally occurring nucleotides, and the like. The nucleic acids may be oligonucleotides, polynucleotides, including cDNAs, mRNAs, peptide-nucleic acids and the like. Where the polymeric compounds are nucleic acids, the nucleic acids will generally be at least about 5 nt, usually at least about 10 nt and more usually at least about 15 nt in length, where the nucleic acids may be as long as 5000 nt or longer, but generally will not exceed about 3000 nt in length and usually will not exceed about 2000 nt in length. In many embodiments, the nucleic acids are at least about 25 nt in length, usually at least about 50 nt in length and may be at least about 100 nt in length.
The polymers are characterized by having a functional moiety that reacts with the ligand reactive functional moiety present on the substrate surface to produce a covalent bond between the ligand and the substrate surface. The ligand may naturally include the desired reactive functionality, or may be modified to include the desired reaction functionality. Representative reactive functionalities of interest include, but are not limited to: amine groups, hydroxyl groups, sulfhydryl, phosphoramidite, anhydrides, and the like.
The polymers employed in the methods may be prepared using any convenient methodology. The particular means of preparing the polymer to include the requisite reactive group where it is not initially present will depend on the nature of the polymer and the nature of the reactive group that is to be incorporated into the polymer.
As mentioned above, in practicing the methods, typically at least two distinct polymers are contacted with the substrate surface that bears the reactive ligand functionalities. By distinct is meant that the two polymers differ from each other in terms of sequence of monomeric units. The number of different polymers that are contacted with the substrate surface may vary depending on the desired nature of the array to be produced, i.e. the desired density of polymeric structures. Generally, the number of distinct polymers that are contacted with the surface of the array will be at least about 5, usually at least about 10 and more usually at least about 100, where the number may be as high as 1,000,000 or higher, but in many embodiments will not exceed about 500,000 and in certain embodiments will not exceed about 100,000.
The polymers are generally contacted with the surface in an aqueous solvent, such that aqueous conditions are established at the surface location to which the polymer is to be covalently attached. The temperature during contact typically ranges from about 10 to about 60 and usually from about 20 to about 40° C. Following initial contact, the aqueous solution of polymer is typically maintained for a period of time sufficient for the desired amount of reaction to occur, where the period of time is typically at least about 20 sec, usually at least about 1 min and more usually at least about 10 min, where the period of time may be as great as 20 min or greater.
Each polymer is typically contacted with the substrate surface as part of an aqueous composition, i.e. an aqueous composition of the polymer in an aqueous solvent is contacted with the surface of the array. The aqueous solvent may be either water alone or water in combination with a co-solvent, e.g. an organic solvent, and the like. The aqueous composition may also contain one or more additional agents, including: acetic acid, monochloro acetic acid, dichloro acetic acid, trichloro acetic acid, acetonitrile, catalysts, e.g. lanthanide (III) trifluoromethylsulfate, lithium chloride, buffering agents, e.g. sodium phosphate, salts, metal cations, surfactants, enzymes, etc.
The aqueous polymer composition may be contacted with the surface using any convenient protocol. Generally, the aqueous polymer composition is contacted with the surface by depositing the aqueous polymer composition on the surface of the substrate. The aqueous volume may be deposited manually, e.g. via pipette, or through the use of an automated machine or device. A number of devices and protocols have been developed for depositing aqueous solutions onto precise locations of a support surface and may be employed in the present methods. Such devices include “pulse-jet” printing devices, mechanical deposition or pipetting devices and the like. See e.g. U.S. Pat. Nos. 4,877,745; 5,338,688; 5,474,796; 5,449,754; 5,658,802; 5,700,637; and 5,807,552; the disclosures of which are herein incorporated by reference. Robotic devices for precisely depositing aqueous volumes onto discrete locations of a support surface, i.e. arrayers, are also commercially available from a number of vendors, including: Genetic Microsystems; Cartesian Technologies; Beecher Instruments; Genomic Solutions; and BioRobotics.
The amount of fluid that is deposited may vary. For example, volumes ranging from about 1 nl to 1 pl, usually from about 60 to 100 nl may be deposited onto the substrate surface. Following contact and incubation for a period of time and under conditions sufficient for the desired reaction to occur, as described above, the surface of the resultant array may be further processed as desired in order to prepare the array for use, as described below. As such, the array surface may be washed to remove unbound reagent, e.g., unreacted polymer, and the like. Any convenient wash solution and protocol may be employed, e.g., flowing an aqueous wash solution, e.g. water, methanol, acetonitrile, and the like, across the surface of the array, etc. The surface may also be dried and stored for subsequent use, etc.
The above described protocols for array fabrication can be carried out using the devices described in U.S. Patent Nos. U.S. Pat. Nos. 6,242,266; 6,232,072 and 6,180,351; the disclosures of which are herein incorporated by reference.
In-Situ Synthesis in Array Fabrication
As indicated above, the substrate surfaces displaying hydroxyl functional groups can also be employed in in-situ ligand synthesis applications. The in-situ synthesis methods include those described in U.S. Pat. No. 5,449,754 for synthesizing peptide arrays, as well as WO 98/41531 and the references cited therein for synthesizing polynucleotides (specifically, DNA) using phosphoramidite or other chemistry. Such in-situ synthesis methods can be regarded as iterating the sequence of depositing: (a) a protected monomer onto predetermined locations on a substrate to link with either a suitably activated substrate surface (or with a previously deposited deprotected monomer); (b) deprotecting the deposited monomer so that it can now react with a subsequently deposited protected monomer; and (c) depositing another protected monomer for linking. Different monomers may be deposited at different regions on the substrate during any one cycle so that the different regions of the completed array will carry the different biopolymer sequences as desired in the completed array. One or more intermediate further steps may be required in each iteration, such as oxidation and washing steps. The substrate surfaces may also be employed in the well known light directed in-situ polymeric array synthesis protocols, including those described in U.S. Pat. No. 6,329,143.
The above protocol produces ligand arrays that can be employed in a variety of different applications, as described in greater detail below.
Arrays
The invention also provides arrays of polymeric binding agents produced according to the methods described above. The arrays include at least two distinct polymers that differ by monomeric sequence immobilized on e.g., covalently to, different and known locations on the substrate surface. In certain embodiments, each distinct polymeric sequence of the array is typically present as a composition of multiple copies of the polymer on the substrate surface, e.g., as a spot on the surface of the substrate. The number of distinct polymeric sequences, and hence spots or similar structures, present on the array may vary, but is generally at least 2, usually at least 5 and more usually at least 10, where the number of different spots on the array may be as a high as 50, 100, 500, 1000, 10,000 or higher, depending on the intended use of the array. The spots of distinct polymers present on the array surface are generally present as a pattern, where the pattern may be in the form of organized rows and columns of spots, e.g. a grid of spots, across the substrate surface, a series of curvilinear rows across the substrate surface, e.g. a series of concentric circles or semi-circles of spots, and the like. The density of spots present on the array surface may vary, but will generally be at least about 10 and usually at least about 100 spots/cm2, where the density may be as high as 106 or higher, but will generally not exceed about 105 spots/cm2. In other embodiments, the polymeric sequences are not arranged in the form of distinct spots, but may be positioned on the surface such that there is substantially no space separating one polymer sequence/feature from another.
In the broadest sense, the arrays of the invention are arrays of polymeric binding agents, where the polymeric binding agents may be any of: peptides, proteins, nucleic acids, polysaccharides, synthetic mimetics of such biopolymeric binding agents, etc. In many embodiments of interest, the arrays are arrays of nucleic acids, including oligonucleotides, polynucleotides, cDNAs, mRNAs, synthetic mimetics thereof, and the like. Where the arrays are arrays of nucleic acids, the nucleic acids may be covalently attached to the arrays at any point along the nucleic acid chain, but are generally attached at one of their termini, e.g., the 3′ or 5′ terminus. In other embodiments, the arrays are arrays of polypeptides, e.g., proteins or fragments thereof.
Utility
The arrays find use in a variety of different applications, where such applications are generally analyte detection applications in which the presence of a particular analyte in a given sample is detected at least qualitatively, if not quantitatively. Protocols for carrying out such assays are well known to those of skill in the art and need not be described in great detail here. Generally, the sample suspected of comprising the analyte of interest is contacted with an array produced according to the methods under conditions sufficient for the analyte to bind to its respective binding pair member that is present on the array. Thus, if the analyte of interest is present in the sample, it binds to the array at the site of its complementary binding member and a complex is formed on the array surface. The presence of this binding complex on the array surface is then detected, e.g. through use of a signal production system, e.g. an isotopic or fluorescent label present on the analyte, etc. The presence of the analyte in the sample is then deduced from the detection of binding complexes on the substrate surface.
Specific analyte detection applications of interest include hybridization assays in which the nucleic acid arrays of the invention are employed. In these assays, a sample of target nucleic acids is first prepared, where preparation may include labeling of the target nucleic acids with a label, e.g., a member of signal producing system. Following sample preparation, the sample is contacted with the array under hybridization conditions, whereby complexes are formed between target nucleic acids that are complementary to probe sequences attached to the array surface. The presence of hybridized complexes is then detected. Specific hybridization assays of interest which may be practiced using the arrays include: gene discovery assays, differential gene expression analysis assays; nucleic acid sequencing assays, and the like. Patents and patent applications describing methods of using arrays in various applications include: U.S. Pat. Nos. 5,143,854; 5,288,644; 5,324,633; 5,432,049; 5,470,710; 5,492,806; 5,503,980; 5,510,270; 5,525,464; 5,547,839; 5,580,732; 5,661,028; 5,800,992; the disclosures of which are herein incorporated by reference.
Where the arrays are arrays of polypeptide binding agents, e.g., protein arrays, specific applications of interest include analyte detection/proteomics applications, including those described in: U.S. Pat. Nos. 4,591,570; 5,171,695; 5,436,170; 5,486,452; 5,532,128; and 6,197,599; the disclosures of which are herein incorporated by reference; as well as published PCT application Nos. WO 99/39210; WO 00/04832; WO 00/04389; WO 00/04390; WO, 00/54046; WO 00/63701; WO 01/14425; and WO 01/40803; the disclosures of the United States priority documents of which are herein incorporated by reference.
In certain embodiments, the methods include a step of transmitting data from at least one of the detecting and deriving steps, as described above, to a remote location. By “remote location” is meant a location other than the location at which the array is present and hybridization occur. For example, a remote location could be another location (e.g. office, lab, etc.) in the same city, another location in a different city, another location in a different state, another location in a different country, etc. As such, when one item is indicated as being “remote” from another, what is meant is that the two items are at least in different buildings, and may be at least one mile, ten miles, or at least one hundred miles apart. “Communicating” information means transmitting the data representing that information as electrical signals over a suitable communication channel (for example, a private or public network). “Forwarding” an item refers to any means of getting that item from one location to the next, whether by physically transporting that item or otherwise (where that is possible) and includes, at least in the case of data, physically transporting a medium carrying the data or communicating the data. The data may be transmitted to the remote location for further evaluation and/or use. Any convenient telecommunications means may be employed for transmitting the data, e.g., facsimile, modem, internet, etc.
As such, in using an array made by the method of the present invention, the array will typically be exposed to a sample (for example, a fluorescently labeled analyte, e.g., protein containing sample) and the array then read. Reading of the array may be accomplished by illuminating the array and reading the location and intensity of resulting fluorescence at each feature of the array to detect any binding complexes on the surface of the array. For example, a scanner may be used for this purpose which is similar to the AGILENT MICROARRAY SCANNER scanner available from Agilent Technologies, Palo Alto, Calif. Other suitable apparatus and methods are described in U.S. patent application Ser. No. 09/846,125 “Reading Multi-Featured Arrays” by Dorsel et al.; and Ser. No. 09/430,214 “Interrogating Multi-Featured Arrays” by Dorsel et al. As previously mentioned, these references are incorporated herein by reference. However, arrays may be read by any other method or apparatus than the foregoing, with other reading methods including other optical techniques (for example, detecting chemiluminescent or electroluminescent labels) or electrical techniques. (where each feature is provided with an electrode to detect hybridization at that feature in a manner disclosed in U.S. Pat. No. 6,221,583 and elsewhere). Results from the reading may be raw results (such as fluorescence intensity readings for each feature in one or more color channels) or may be processed results such as obtained by rejecting a reading for a feature which is below a predetermined threshold and/or forming conclusions based on the pattern read from the array (such as whether or not a particular target sequence may have been present in the sample). The results of the reading (processed or not) may be forwarded (such as by communication) to a remote location if desired, and received there for further use (such as further processing).
Kits
Kits for use in analyte detection assays are also provided. The kits at least include the arrays of the invention. The kits may further include one or more additional components necessary for carrying out an analyte detection assay, such as sample preparation reagents, buffers, labels, and the like. As such, the kits may include one or more containers such as vials or bottles, with each container containing a separate component for the assay, and reagents for carrying out an array assay such as a nucleic acid hybridization assay or the like. The kits may also include a denaturation reagent for denaturing the analyte, buffers such as hybridization buffers, wash mediums, enzyme substrates, reagents for generating a labeled target sample such as a labeled target nucleic acid sample, negative and positive controls and written instructions for using the array assay devices for carrying out an array based assay. The instructions may be printed on a substrate, such as paper or plastic, etc. As such, the instructions may be present in the kits as a package insert, in the labeling of the container of the kit or components thereof (i.e., associated with the packaging or sub-packaging) etc. In other embodiments, the instructions are present as an electronic storage data file present on a suitable computer readable storage medium, e.g., CD-ROM, diskette.
The following examples are offered by way of illustration and not by way of limitation.
EXAMPLES
I. Production and Characterization of Aldehyde Functionalized Substrates
A. Production
1 ml of water is added to 4 liters of toluene and the mix is stirred overnight or until such time as the water is fully dissolved. Surfaces to be derivatized are placed in 1000 mls of the above toluene. 8 mls of undecyltrichloro acetate (also known as 11-(trichlorosilyl) acetate) is then added slowly to the stirred solvent, over a period of about 10 minutes. The solution is then stirred for a further 2 hours at room temperature, after which the surfaces are rinsed in fresh toluene, then methanol, then water and finally dried in a stream of nitrogen.
The acetate groups are converted to hydroxyl group by placing the above surfaces in a 10% solution of sulfuric acid in water at 50 degrees C. for 30 minutes, after which they are rinsed in water, then dried in a stream of dry nitrogen. A solution of 5 gms of Dess-Martin reagent (1,1-Triacetoxy-1,1-1,2-benziodoxol-3(1H)-one) is then dissolved in 1000 mls of demethylsulfoxide. 0.2 mls of water is then added, followed by the surfaces to be derivatized. This step converts the hydroxy groups to aldehyde groups.
After stirring overnight the surfaces are removed from the Dess-Martin solution and rinsed in toluene, then methanol, then water and finally dried in a stream of dry nitrogen.
A schematic of the above protocol is provided in FIG. 1.
B. Contact Angle Determination
Approximately 25 μl of water was dropped onto the derivatized surface. The contact angle was measured with a FTA (First Ten Angstroms) 200 goniometer with software provided by Accusoft Corp.
Typical results for the contact angle for a 100% surface (i.e. surfaces made using only the acetate silane as starting material) are, for the final aldehyde surface, about 76 degrees.
II. Production and Characterization of Carbonylimidazole Functionalized Surfaces via a Carboxylic Acid Derivative.
A. Production
1 ml of water is added to 4 liters of toluene and the mix stirred overnight or until such time as the water is fully dissolved. To 1000 mls of the above toluene is added 4 mls of undecenyltrichlorosilane and 4 mls of decyltrichlorosilane. To the above solution are added the surfaces to be derivatized. After the solution has been stirred at room temperature for 2 hours the surfaces are rinsed in fresh toluene, then methanol, then water and finally dried in a stream of dry nitrogen.
The vinyl groups on the surface are then oxidized to carboxylic acid groups by the method of Whitesides et al (Langmuir 1989, 5, 1074–1087). Stock solutions of potassium permangante (5 mM), sodium periodate (195 mM) and potassium carbonate (18 mM) were prepared. Immediately prior to oxidation 100 mls of each of these solutions were added to 700 mls of water. The surfaces were then placed in this mixture overnight.
The surfaces were rinsed in sodium bisulfite, water, 0.1N hydrochloric acid and finally with water, after which they were dried in a stream of dry nitrogen. 10 gms of 1,1′ carbonyldiimidazole were stirred in 1000 mls of anhydrous dimethylformaide. After dissolution the surfaces were placed in the solution and stirred for 2 hours at room temperature. The surfaces were then rinsed in methanol, water and finally dried in a stream of dry nitrogen.
A schematic of the above protocol is provided in FIG. 2.
B. Contact Angle Determination
Contact angles were measured as described above. A typical contact angle for a 50% carbonylimidazole surface is about 80 degrees.
III. Production and Characterization of Ligand Array Produced from Aldehyde Functionalized Surfaces.
Solutions of 25mer and 60mer yeast probes, either amine or non-amine terminated, probes were spotted onto the surface. After passivation these probes were hybridized with both CY# K562 and CY % Hela RNA targets in a buffer solution. The fluorescence signal from the CY3 and CY5 tags was found to be high and showed high specificity between amine and non-amine probes.
IV. Production and Characterization of Ligand Array Produced from Carbonylimdazole Surfaces Prepared via a Carboxylic Acid Derivative:
These surfaces were tested in a similar fashion to the aldehyde surfaces. Similar results were also observed.
It is evident from the above results and discussion that an important new protocol for preparing polymeric arrays, particularly nucleic acid arrays, is provided by the subject invention. The methods for modification of the substrate surfaces are safe and readily provide functionalized surfaces that retain a high contact angle, thereby providing desirable spotting properties on the array. Additionally, arrays produced from the subject modified substrates exhibit low background signals and low non-specific target binding. Accordingly, the subject invention represents a significant contribution to the art.
All publications and patent applications cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention.
Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.

## Claims

1. A method of producing an array of at least two different ligands covalently bonded to a surface of a substrate, said method comprising:
(a) contacting a surface of a substrate with a silanizing reagent comprising an acetate functional group to produce a surface displaying acetate functional groups;
(b) converting said acetate functional groups on said surface to hydroxyl functional groups by acid or alkali hydrolysis; and
(c) contacting said surface displaying hydroxyl functional groups with at least two different ligands to produce said army;
with the proviso that said method further comprises converting said hydroxyl functional groups to ligand reactive functional groups when said hydroxyl functional groups do not covalently bond to said ligands upon contact.

2. The method according to claim 1, wherein said silanizing reagent comprises silyl and acetate groups separated by an alkyl chain.

3. The method according to claim 2, wherein said alkyl chain is from about 6 to about 20 carbon atoms in length.

4. The method according to claim 3, wherein said silanizing reagent has the formula:


Ac-(L)-Si(RLRXRY) wherein:

RL is a leaving group;
RX and RY are independently lower alkyl or a leaving group;
L is a C8–C18 alkyl chain; and
Ac is an acetate group.

5. The method according to claim 4, wherein said acetate group has the formula:


—O(CO)CR1R2R3;


wherein:
R1, R2, and R3 are independently chosen from H, halogen, alkyoxy, aryloxy, alkyl, alyl, heteroalkyl, heteroaryl.

6. The method according to claim 4, wherein said silane reagent is 11-trichlorosilyl-undecyl acetate.

7. The method according to claim 1, wherein said acetate functional groups are converted to said hydroxyl functional groups by hydrolysis.

8. The method according to claim 1, wherein said method comprises converting said hydroxyl functional group to a ligand reactive functional group.

9. The method according to claim 8, wherein said ligand reactive functional group is an aldehyde.

10. The method according to claim 1, wherein said substrate is glass.

11. The method according to claim 1, wherein said ligand are selected from the group comprising oligonucleotides, polynucleotides, peptide-nucleic acids or peptides.

12. The method according to claim 1, wherein said polynucleotides are cDNA.

13. A ligand array produced according to the method of claim 1.

14. A method of detecting the presence of an analyte in a sample, said method comprising;
(a) contacting a sample suspected of comprising said analyte with a ligand array according to claim 13;
(b) detecting any binding complexes on the surface of the said array to obtain binding complex data; and
(c) determining the presence of said analyte in said sample using said binding complex data.

15. The method according to claim 14, wherein said analyte is a nucleic acid.

16. The method according to claim 14, wherein said method further comprises a data transmission step in which a result from a reading of said array is transmitted from a first location to a second location.

17. A method according to claim 16, wherein said second location is a remote location.

18. A method comprising receiving data representing a result of a reading obtained by the method of claim 16.

19. A kit for use in an analyte detection assay, said kit comprising:
a ligand array according to claim 13.

20. A method of producing an array of at least two different ligands covalently bonded to a surface of a substrate, said method comprising:
(a) contacting a surface of a substrate with a silanizing reagent comprising an acetate functional group to produce a surface displaying acetate functional groups;
(b) converting said acetate functional groups on said surface to hydroxyl functional groups; and
(c) converting said hydroxyl functional groups to aldehyde groups by controlled oxidation, wherein the controlled oxidation is a Moffat oxidation or is effected with Dess-Martin solution.

21. The method according to claim 20, wherein the controlled oxidation is a Moffat oxidation.

22. The method according to claim 20, wherein the controlled oxidation is effected with Dess-Martin solution.

23. The method according to claim 1, wherein a single silanizing reagent is used.