Patent Publication Number: US-2021164881-A1

Title: Fluidic cartridge for cytometry and additional analysis

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/211,175, filed on Dec. 5, 2018, which is a continuation of U.S. patent application Ser. No. 15/803,133, filed on Nov. 3, 2017, the disclosure of which are incorporated by reference herein in their entireties. 
     This application claims priority to U.S. Provisional Patent Application No. 62/497,075, filed on Nov. 7, 2016, entitled “Fluidic Cartridge for Cytometry and Additional Analysis”, the entire contents of which are incorporated herein by reference and relied upon. 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/176,729, filed on Jun. 8, 2016, entitled “Fluidic Units and Cartridges for Multi-Analyte Analysis”, which claims priority to U.S. Provisional Patent Application No. 62/174,776, filed on Jun. 12, 2015, the entire contents of each of which are incorporated herein by reference and relied upon. 
     This application is related to International Application PCT/US2016/036426, filed on Jun. 8, 2016, entitled “Fluidic Units and Cartridges for Multi-Analyte Analysis”, which claims priority to U.S. Provisional Patent Application No. 62/174,776, filed on Jun. 12, 2015, the entire contents of each of which are incorporated herein by reference and relied upon. 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/209,226, filed on Jul. 13, 2016, entitled “Volume Sensing in Fluidic Cartridge”, which claims priority to U.S. Provisional Patent Application No. 62/192,488, filed on Jul. 14, 2015, the entire contents of each of which are incorporated herein by reference and relied upon. 
     This application is related to International Application PCT/US2016/042089, filed on Jun. 13, 2016, entitled “Volume Sensing in Fluidic Cartridge”, which claims priority to U.S. Provisional Patent Application No. 62/192,488, filed on Jul. 14, 2015, the entire contents of each of which are incorporated herein by reference and relied upon. 
    
    
     FIELD OF THE DISCLOSURE 
     The disclosure relates to medicine and cytometry. 
     BACKGROUND 
     All publications cited herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. The following description includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art or relevant to the presently disclosure, or that any publication specifically or implicitly referenced is prior art. 
     Flow cytometry is a popular tool for cellular analysis of biological samples. Typical cytometry analyses involve two parts. The first part is sample preparation. For example, some cytometry analyses label target cells with a specific fluorophore, so that these cells can be detected by an optical measurement of fluorescence signals. In another example, some cytometry analyses require selectively lysing cells in samples, leaving only target cells intact for cytometry measurement. The second part is sample analysis. Usually, the sample stream is focused into a narrow stream when flowing through a flow cell, where the target cells are measured one by one for optical or other signals. This narrow sample stream is usually obtained by hydrodynamic focusing of sheath flow. 
     The signal measured in flow cytometry can be used to evaluate individual target cells&#39; characteristics, such as cell size and cell surface roughness. With the help of fluorescent labeling, additional cellular characteristics can also be evaluated such as the existence of a cellular nucleus, the amount of DNA inside the cell, antigens on a cellular membrane, and many other characteristics. As the cells are measured one by one, the total number of target cells detected can also be determined by counting the number of measured signal peaks. Additionally, some cytometry analyses also require measuring particle density in the sample, meaning the number of target particles per sample volume, which is also known as the absolute count in cytometry analyses. For this measurement, not only the total number of detected particles needs to be determined, but also the corresponding volume of the sample needs to be determined. These two pieces of information can be used together to calculate the number of particles per sample volume, e.g., the absolute count. 
     In conventional flow cytometry analyses, the sample preparation steps are usually carried out by manual operation. For example, the preparation steps are often performed in different containers, such as centrifugal tubes or vials, and only the final prepared sample is then loaded into a commercial cytometer for optical or other measurement. These manual steps of sample preparation require precise fluid handling by trained technicians and are thus not suitable for applications where users are minimally trained. 
     Furthermore, for applications such as the point-of-care testing in medical diagnostics, the cytometry analyses are performed in a non-laboratory environment, such as in emergency rooms or physician offices. Therefore, it is important that the biological sample is self-contained and not exposed to environment causing biological contaminations. For this purpose, it is advantageous that both the sample preparation step and the measurement step are carried out in a self-contained manner such as inside a non-exposed container. 
     Additionally, the absolute count measurement requires that the total number of detected target cells and corresponding sample volume be known. In conventional cytometry analyses, a fixed amount of sample with a known volume is injected into the system to determine the absolute count. However, the fluidic system often introduces dead volumes, meaning that some portion of the sample does not go through the cytometer measurement. These dead volumes cause the real sample volume being measured to be different from the known volume being injected into the system, and therefore introduce inaccuracy to the absolute count. 
     With above considerations, there is a need to develop a fluidic cartridge that can perform the cytometry analysis in a self-contained, automated manner, including both the sample preparation and sample analysis steps. There is also a need that such a fluidic cartridge can perform not only a cytometry analysis and cell count, but also accurately measure the absolute count. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with devices, systems and methods which are meant to be exemplary and illustrative, not limiting in scope. 
     The present disclosure provides various fluidic cartridges and methods of using and making such fluidic cartridges. These fluidic cartridges can perform both the sample preparation and the cytometer analysis. These fluidic cartridges can be used for various types of cytometry analyses. In various embodiments, the fluidic cartridges as disclosed herein can be used to determine the absolute count. In various embodiments, the fluidic cartridges as disclosed herein can be used for DNA analysis of cell populations in tumor diagnosis. In various embodiments, the fluidic cartridges as disclosed herein can be used for CD4+/CD8+ lymphocyte subtype analyses in AIDS diagnosis. In various embodiments, the fluidic cartridges as disclosed herein can be used for cell analysis in complete blood count (CBC). These fluidic cartridges can also be used for other types of analyses including, but not limited to, analyzing analytes, proteins, enzymes, nucleic acids, and other biological markers in samples. 
     Various embodiments of the present disclosure provide a device for analyzing target particles in a sample. In various embodiments, the device comprises a cartridge device. In various embodiments, the cartridge device comprises: an inlet configured for receiving the sample into the cartridge device; a fluidic structure fluidly connected to the inlet and configured for mixing at least a portion of the sample with at least a portion of a reagent to form one or more sample mixtures; a flow cell fluidly connected to the fluidic structure and configured for forming one or more sample streams from the one or more sample mixtures, wherein the sample streams are formed in the flow cell without a sheath flow, and wherein the flow cell comprises an optically transparent area configured for measuring an optical signal from the sample streams to detect the target particles in the sample; and a flow sensor fluidly connected to the flow cell and configured for measuring a sensing signal from the sample streams that enter the flow sensor. In various embodiments, a cartridge device as disclosed herein further comprises a reagent. 
     In various embodiments, a device as disclosed herein further comprises a reader instrument device, wherein the reader instrument device is configured for receiving, operating, and/or actuating the cartridge device. In various embodiments, the reader instrument device neither receives any liquid from the cartridge device nor transfers any liquid into the cartridge device. 
     Various embodiments of the present disclosure provide a method for analyzing target particles in a sample. The method comprises: applying the sample to a cartridge device as disclosed herein, which is configured for collecting a predetermined sample volume into the cartridge device; transferring the cartridge device into a reader instrument device as disclosed herein; mixing at least a portion of the collected sample and at least a portion of a reagent to form one or more sample mixtures inside the cartridge device; forming one or more sample streams from the one or more sample mixtures in a flow cell inside the cartridge device, wherein the sample streams are formed in the flow cell without a sheath flow; measuring an optical signal from the sample streams at the flow cell to detect the target particles in the sample streams; and using the reader instrument device to analyze the measured optical signal to quantify the target particles in the sample. 
     Various embodiments of the present disclosure provide a method for analyzing particles in a sample. The method comprises: applying the sample to a cartridge device as disclosed herein, which is configured for collecting a predetermined sample volume into the cartridge device; transferring the cartridge device into a reader instrument device as disclosed herein; mixing at least a portion of the collected sample and at least a portion of a reagent to form one or more sample mixtures inside the cartridge device; forming one or more sample streams from the one or more sample mixtures in a flow cell inside the cartridge device, wherein at least two separate sample mixtures are transferred into the same flow cell to form at least two separate sample streams without a sheath flow; measuring an optical signal from the sample streams at the flow cell to detect the target particles in the sample streams; and using the reader instrument device to analyze the measured optical signal to quantify the target particles in the sample. 
     In various embodiments, a method as disclosed herein further comprises: flowing the sample streams through a flow sensor that is fluidly connected to the flow cell; measuring a sensing signal from the sample streams at the flow sensor to detect the entrance of the sample streams into the flow sensor and/or the exit of the sample streams out of the flow sensor; and using the reader instrument device to analyze the measured optical signal and sensing signal to determine the concentration of the target particles in the sample. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are illustrated in referenced figures. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
         FIG. 1  illustrates, in accordance with various embodiments of the disclosure, one non-limiting example of the basic fluidic unit used in a cartridge device as disclosed herein. 
         FIGS. 2A-2D  illustrate, in accordance with various embodiments of the disclosure, a few non-limiting examples of passive valves. 
         FIGS. 3A-3C  illustrate, in accordance with various embodiments of the disclosure, a few non-limiting examples of active valves. 
         FIGS. 4A-4C  illustrate, in accordance with various embodiments of the disclosure, one non-limiting example of implementing a passive valve in a basic fluidic unit. 
         FIG. 5  illustrates, in accordance with various embodiments of the disclosure, a symbol drawing that represents a basic fluidic unit as described herein. 
         FIGS. 6A-6B  illustrate, in accordance with various embodiments of the disclosure, one non-limiting example of a sheathless flow cell as described herein and its symbolic drawing. 
         FIGS. 7A-7B  illustrate, in accordance with various embodiments of the disclosure, one non-limiting example of a flow sensor as described herein, which has two sensing zones along the length of a fluidic channel, and its symbolic drawing. 
         FIGS. 8A-8B  illustrate, in accordance with various embodiments of the disclosure, another non-limiting example of a flow sensor as described herein, which has only one sensing zone along the length of a fluidic channel, and its symbolic drawing. 
         FIGS. 9A-9C  illustrate, in accordance with various embodiments of the disclosure, one exemplary configuration of a cartridge device as disclosed herein, where a basic fluidic unit  9001 , a sheathless flow cell  9007  and a flow sensor  9009  with two sensing zones  9011  and  9012  are connected in serial by fluidic conduits  9006  and  9008 . 
         FIGS. 10A-10B  illustrate, in accordance with various embodiments of the disclosure, another exemplary configuration of a cartridge device as disclosed herein, where a flow sensor  10007  is connected to the microfluidic channel  10004  of a basic fluidic unit  10001  with a fluidic conduit  10006 . 
         FIGS. 11A-11B  illustrate, in accordance with various embodiments of the disclosure, another exemplary configuration of a cartridge device as disclosed herein, where a basic fluidic unit  11001 , a sheathless flow cell  11007  and a flow sensor  11009  with one sensing zone  11012  are connected in serial by fluidic conduits  11006  and  11008 . 
         FIGS. 12A-12G  illustrate, in accordance with various embodiments of the disclosure, another exemplary configuration of a cartridge device as disclosed herein, where two basic fluidic units  12101  and  12201  are used in serial with a sheathless flow cell  12301  and a flow sensor  12401 . 
         FIGS. 13A-13C  illustrate, in accordance with various embodiments of the disclosure, another exemplary configuration of a cartridge device as disclosed herein, where three basic fluidic units  13101 ,  13201  and  13301  are used in serial with a sheathless flow cell  13401  and a flow sensor  13501 . 
         FIGS. 14A-14B  illustrate, in accordance with various embodiments of the disclosure, another exemplary configuration of a cartridge device as disclosed herein, where four basic fluidic units  14101 ,  14201 ,  14301  and  14401  are used in serial with a sheathless flow cell  14501  and a flow sensor  14601 . 
         FIGS. 15A-15D  illustrate, in accordance with various embodiments of the disclosure, the top view (in x-y plane) of a few examples of a flow cell as described herein. 
         FIGS. 16A-16B  illustrate, in accordance with various embodiments of the disclosure, an example where a plurality of particles flow through a flow cell for detection. 
         FIGS. 17A-17D  illustrate, in accordance with various embodiments of the disclosure, exemplary designs for determining the absolute count of particles, where the outlet  17103  of the flow cell  17101  is coupled to the inlet  17202  of the flow sensor  17201  by a fluidic conduit  17001 . 
         FIGS. 18A-18B  illustrate, in accordance with various embodiments of the disclosure, another exemplary design for determining the absolute count of particles, where the inlet  18102  of the flow cell  18101  is coupled to the outlet  18203  of the flow sensor  18201  by a fluidic conduit  18001 . 
         FIG. 19  illustrates, in accordance with various embodiments of the disclosure, one non-limiting example of an analyzer having a cartridge device and a reader instrument device. The cartridge  19101  having the fluidic structure  19102  can be inserted into a docking slot  19202  on the reader instrument  19201 . 
         FIGS. 20A-20B  illustrate, in accordance with various embodiments of the disclosure, exemplar processes for building a sheathless flow cell as described herein. 
     
    
    
     DETAILED DESCRIPTION 
     All references cited herein are incorporated by reference in their entirety as though fully set forth. 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 this disclosure belongs. Tabelling, Introduction to Microfluidics reprint edition, Oxford University Press (2010); Hguyen et al., Fundamentals and Applications of Microfluidics 2nd ed., Artech House Incorporated (2006); Berg et al., Microfluidics for Medical Applications, Royal Society of Chemistry (2014); Gomez et al., Biological Applications of Microfluidics 1st ed., Wiley-Interscience (2008); and Colin et al., Microfluidics 1st ed., Wiley-ISTE (2010), provide one skilled in the art with a general guide to many of the terms used in the present application. 
     One skilled in the art will recognize many methods and materials similar or equivalent to those described herein, which could be used in the practice of the present disclosure. Other features and advantages of the disclosure will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, various features of embodiments of the disclosure. Indeed, the present disclosure is in no way limited to the methods and materials described. For convenience, certain terms employed herein, in the specification, examples and appended claims are collected here. 
     Unless stated otherwise, or implicit from context, the following terms and phrases include the meanings provided below. Unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired in the art to which it pertains. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It should be understood that this disclosure is not limited to the particular methodology, protocols, and reagents, etc., described herein and as such can vary. The definitions and terminology used herein are provided to aid in describing particular embodiments and are not intended to limit the claims. 
     As used herein the term “comprising” or “comprises” is used in reference to compositions, methods, and respective component(s) thereof, that are useful to an embodiment, yet open to the inclusion of unspecified elements, whether useful or not. It will be understood by those within the art that, in general, terms used herein 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.). 
     Unless stated otherwise, the terms “a” and “an” and “the” and similar references used in the context of describing a particular embodiment of the application (especially in the context of claims) can be construed to cover both the singular and the plural. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicate herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (for example, “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the application and does not pose a limitation on the scope of the application otherwise claimed. The abbreviation, “e.g.” is derived from the Latin exempli gratia, and is used herein to indicate a non-limiting example. Thus, the abbreviation “e.g.” is synonymous with the term “for example.” No language in the specification should be construed as indicating any non-claimed element essential to the practice of the application. 
     Various embodiments of the present disclosure provide a device for analyzing target particles in a sample. In various embodiments, the device comprises a cartridge device. In various embodiments, the cartridge device comprises: an inlet configured for receiving the sample into the cartridge device; a fluidic structure fluidly connected to the inlet and configured for mixing at least a portion of the sample with at least a portion of a reagent to form one or more sample mixtures; a flow cell fluidly connected to the fluidic structure and configured for forming one or more sample streams from the one or more sample mixtures, wherein the sample streams are formed in the flow cell without a sheath flow, and wherein the flow cell comprises an optically transparent area configured for measuring an optical signal from the sample streams to detect the target particles in the sample; and a flow sensor fluidly connected to the flow cell and configured for measuring a sensing signal from the sample streams that enter the flow sensor. 
     In various embodiments, the cartridge device has a size in the range of about 0.1-1 cm 3 , 1-5 cm 3 , 5-25 cm 3 , 25-50 cm 3 , or 50-200 cm 3 . 
     In various embodiments, a device as disclosed herein further comprises a reader instrument device, wherein the reader instrument device is configured for receiving, operating, and/or actuating the cartridge device. In various embodiments, the reader instrument device is configured for measuring the optical signal at the flow cell to quantify the target particles in the sample. In various embodiments, the reader instrument device is configured for measuring the sensing signal at the flow sensor to quantify the volume of the sample streams. In various embodiments, the reader instrument device is configured for measuring the optical signal at the flow cell and the sensing signal at the flow sensor to determine the concentration of the target particles in the sample. In various embodiments, the reader instrument device comprises a control unit configured for measuring the optical signal at the flow cell. In various embodiments, the reader instrument device comprises a control unit configured for measuring the optical signal at the flow cell and the sensing signal at the flow sensor. In various embodiments, the reader instrument device neither receives any liquid from the cartridge device nor transfers any liquid into the cartridge device. 
     In various embodiments, a cartridge device as disclosed herein further comprises a reagent. In various embodiments, the reagent comprises a fluorescent labeling agent that selectively labels the target particles in the sample with fluorescence, and wherein the optical signal from the sample streams comprises fluorescence. 
     In various embodiments, a cartridge device as disclosed herein further comprises a first reagent, which is mixed with a portion of the received sample to form a first sample mixture, and a second reagent, which is mixed with another portion of the received sample to form a second sample mixture; and the two sample mixtures are separately transferred into the flow cell to form two separate sample streams. In various embodiments, the two sample mixtures are separately formed in a chamber or separately transferred into a chamber before being separately transferred into the flow cell. In various embodiments, the chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. 
     In various embodiments, a cartridge device as disclosed herein further comprises a fluidic conduit fluidly connected to the inlet and configured for receiving or collecting the sample. In various embodiments, the fluidic conduit is closed by a valve and/or sealed by an external structure after the sample is collected into the fluidic conduit. In accordance with various embodiments of the present disclosure, closing by the value and/or sealing by the external structure prevents the collected sample from exiting the cartridge device. In various embodiments, the fluidic conduit is configured for collecting a predetermine sample volume in the range of about 0.1-1 μL, 1-5 μL, 5-10 μL, 10-20 μL, or 20-50 μL. In various embodiments, at least a portion of the reagent is transferred into the fluidic conduit to flush a portion of the collected sample into a chamber to form a sample mixture. 
     In various embodiments, the sample, reagent, sample mixtures, or sample streams are enclosed inside the cartridge device to prevent or limit their exposure to the environment outside the cartridge. In various embodiments, the fluidic structure is inside the cartridge device to prevent or limit exposing the sample, reagent, or sample mixtures to the environment outside the cartridge. In various embodiments, the flow cell is inside the cartridge device to prevent or limit exposing the sample streams to the environment outside the cartridge. In various embodiments, the flow sensor is inside the cartridge device to prevent or limit exposing the sample streams to the environment outside the cartridge. 
     In various embodiments, the fluidic structure comprises one or a plurality of fluidic conduits. In various embodiments, the fluidic structure comprises one or a plurality of chambers. In various embodiments, each chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. In certain embodiments, the fluidic structure comprises one or a plurality of chambers; each chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml; and the fluidic structure is configured for transferring the sample mixtures from one of the chambers to the flow cell to form the sample streams. 
     In some embodiments, a cartridge device as disclosed here comprises one flow cell. In some embodiments, a cartridge device as disclosed comprises two, three, four, five, or more flow cells. In some embodiments, a cartridge device as disclosed comprises a plurality of flow cells. 
     In various embodiments, the flow cell is configured for allowing a flow rate in the range of 0.001-0.01, 0.01-0.1, 0.1-1, 1-50, 50-200, or 200-1000 μl/min. In various embodiments, the flow cell has a cross section in the shape of a rectangular, trapezoid, oval, circle, or half circle, or any other shape, or a combination thereof. In various embodiments, the flow cell has a width in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm. In various embodiments, the flow cell has a depth in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm. In various embodiments, the flow cell has a length in the range of about of 1-10 μm, 10-100 μm, 100-1,000 μm, 1,000-10,000 μm, or 10,000-50,000 μm. In various embodiments, the sample streams formed in the flow cell have a cross section of the same size as the flow cell. 
     In certain embodiments, the flow cell has a width in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm and a depth in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm; and the sample streams have a cross section of the same size as the flow cell. 
     In various embodiments, the optically transparent area on the flow cell has a transmission rate of 50-60%, 60-70%, 70-80%, 80-90%, 90-96%, or 96-99.9% for the optical signal from the sample streams. In various embodiments, the optical signal comprises scattered light, reflected light, transmitted light, fluorescence, light absorption, light extinction, or white light image, or a combination thereof. In certain embodiments, the optically transparent area on the flow cell has a transmission rate of 50-60%, 60-70%, 70-80%, 80-90%, 90-96%, or 96-99.9% for the optical signal from the sample streams, and the optical signal comprises scattered light, reflected light, transmitted light, fluorescence, light absorption, light extinction, or white light image, or a combination thereof. 
     In various embodiments, the optically transparent area on the flow cell is made of a plastic material. In various embodiments, the plastic material is cyclic olefin copolymer, cyclo-olefin polymer, poly-methyl methacrylate, polycarbonate, polystyrene, or poly-chloro-tri-fluoro-ethylene, or a combination thereof. 
     In various embodiments, the flow sensor comprises a fluidic channel and a sensing zone on the fluidic channel; the fluidic channel is fluidly connected to the flow cell to allow the sample streams to flow through; and a sensing signal is measured when the sample streams enter the sensing zone. In various embodiments, the sensing signal comprises an optical signal. In certain embodiments, the optical signal comprises light transmission through and/or light reflection from the sample streams. 
     In various embodiments, the fluidic channel in the flow sensor has a channel width in the range of about 0.001-0.05 mm, 0.05-1 mm, or 1-5 mm, and a channel depth in the range of about 0.001-0.01 mm, 0.01-0.5 mm, 0.5-1 mm, or 1-2 mm. In various embodiments, the flow cell and the flow sensor are configured to have the same flow rate for the sample streams flowing through. In various embodiments, the fluidic connection between the flow cell and the flow sensor is configured for a sample stream to have the same flow rate flowing through the flow cell and the flow sensor. 
     In various embodiments, the sensing zone comprises an optically transparent area configured for measuring an optical signal that changes levels between the absence and presence of the sample streams in the sensing zone. In various embodiments, the optically transparent area on the sensing zone has a transmission rate of 50-60%, 60-70%, 70-80%, 80¬90%, 90-96%, or 96-99.9% for the optical signal from the sample streams. In various embodiments, the optical signal comprises scattered light, reflected light, transmitted light, fluorescence, light absorption, light extinction, or white light image, or a combination thereof. In various embodiments, the optically transparent area on the sensing zone is made of a plastic material. In various embodiments, the plastic material is cyclic olefin copolymer, cyclo-olefin polymer, poly-methyl methacrylate, polycarbonate, polystyrene, or poly-chloro-tri-fluoro-ethylene, or a combination thereof. 
     In some embodiments, the flow sensor comprises one sensing zone on the fluidic channel. In some embodiments, the flow sensor comprises two, three, four, five, or more sensing zones on the fluidic channel. In some embodiments, the flow sensor comprises a plurality of sensing zones on the fluidic channel. 
     In various embodiments, the fluidic structure comprises at least one basic fluidic unit that comprises: a chamber configured to accommodate a fluid; a venting port connected to the chamber, wherein the venting port is connected to a pneumatic pressure source, an ambient pressure, or the atmosphere pressure; a microfluidic channel connected to the chamber; and a valve on the microfluidic channel. In various embodiments, the cartridge device is configured for transferring the sample mixtures from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device. 
     In various embodiments, the cartridge device is configured for transferring the sample mixtures from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device. In various embodiments, the external actuation mechanism comprises a pneumatic pressure source. In various embodiments, the external actuation mechanism is configured for forming the sample streams with a flow rate in the range of 0.001-0.01, 0.01-0.1, 0.1-1, 1-50, 50-200, or 200-1000 μl/min. In certain embodiments, the cartridge device is configured for transferring the sample mixtures from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device, and the external actuation mechanism comprises a pneumatic pressure source. 
     In various embodiments, the chamber of the basic fluidic unit has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. In various embodiments, the microfluidic channel of the basic fluidic unit has a cross section of a size in the range of about 0.001-0.01 mm 2 , 0.01-0.1 mm 2 , 0.1-0.25 mm 2 , 0.25-0.5 mm 2 , 0.5-1 mm 2 , 1-2 mm 2 , or 2-10 mm 2 . In certain embodiments, the chamber of the basic fluidic unit has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml, and the microfluidic channel of the basic fluidic unit has a cross section of a size in the range of about 0.001-0.01 mm 2 , 0.01-0.1 mm 2 , 0.1-0.25 mm 2 , 0.25-0.5 mm 2 , 0.5-1 mm 2 , 1-2 mm 2 , or 2-10 mm 2 . 
     In various embodiments, when the cartridge device is in use, the chamber of the basic fluidic unit is so positioned that the at least a portion of the fluid inside the chamber is pulled by gravity towards the microfluidic channel and/or away from the venting port. In various embodiments, when the cartridge device is in use, the chamber of the basic fluidic unit has a volume larger than the volume of the fluid accommodated therein and an air gap exists between the venting port and the fluid accommodated therein. 
     In various embodiments, the valve of the basic fluidic unit is a passive valve that is configured for allowing a fluid flow to pass through the microfluidic channel when a pneumatic pressure is applied to the fluid flow and stopping the fluid flow when no pneumatic pressure is applied to the fluid flow. In various embodiments, the valve of the basic fluidic unit is a passive valve that comprises one of the following structures: (i) a channel with a hydrophilic inner surface embedded with a patch of a hydrophobic surface, (ii) a channel with a hydrophobic inner surface embedded with a patch of a hydrophilic surface, (iii) an enlargement of the channel cross section along the flow direction in a channel with a hydrophilic inner surface, and (iv) a contraction of the channel cross section along the flow direction in a channel with a hydrophobic inner surface. In various embodiments, the valve of the basic fluidic unit is an active valve operated by an actuation mechanism external to the cartridge device. 
     Various embodiments of the present disclosure provide a method for analyzing particles in a sample. The method comprises: providing a cartridge device as disclosed herein and a reader instrument device as disclosed herein; applying the sample to the cartridge device; transferring the cartridge device into the reader instrument device; operating the reader instrument device to actuate the cartridge device; and analyzing the target particles in the sample. 
     Various embodiments of the present disclosure provide a method for analyzing target particles in a sample. The method comprises: applying the sample to a cartridge device as disclosed herein, which is configured for collecting a predetermined sample volume into the cartridge device; transferring the cartridge device into a reader instrument device as disclosed herein; mixing at least a portion of the collected sample and at least a portion of a reagent to form one or more sample mixtures inside the cartridge device; forming one or more sample streams from the one or more sample mixtures in a flow cell inside the cartridge device, wherein the sample streams are formed in the flow cell without a sheath flow; measuring an optical signal from the sample streams at the flow cell to detect the target particles in the sample streams; and using the reader instrument device to analyze the measured optical signal to quantify the target particles in the sample. 
     Various embodiments of the present disclosure provide a method for analyzing target particles in a sample. The method comprises: applying the sample to a cartridge device as disclosed herein, which is configured for collecting a predetermined sample volume into the cartridge device; transferring the cartridge device into a reader instrument device as disclosed herein; mixing at least a portion of the collected sample and at least a portion of a reagent to form one or more sample mixtures inside the cartridge device; forming one or more sample streams from the one or more sample mixtures in a flow cell inside the cartridge device, wherein at least two separate sample mixtures are transferred into the same flow cell to form at least two separate sample streams without a sheath flow; measuring an optical signal from the sample streams at the flow cell to detect the target particles in the sample streams; and using the reader instrument device to analyze the measured optical signal to quantify the target particles in the sample. 
     In various embodiments, a portion of the collected sample is mixed with a first reagent to form a first sample mixture and another portion of the collected sample is mixed with a second reagent to form a second sample mixture; and the two sample mixtures are separately transferred into the flow cell to form two separate sample streams. In various embodiments, the two sample mixtures are separately formed in a chamber or separately transferred into a chamber before being separately transferred into the flow cell. In various embodiments, the chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. 
     In various embodiments, the sample is collected into a fluidic conduit. In various embodiments, the fluidic conduit is closed by a valve and/or sealed by an external structure after the sample is collected into the fluidic conduit. In accordance with various embodiments of the present disclosure, closing by the value and/or sealing by the external structure prevents the collected sample from exiting the cartridge device. In various embodiments, the fluidic conduit is configured for collecting a predetermine sample volume in the range of about 0.1-1 μL, 1-5 μL, 5-10 μL, 10-20 μL, or 20-50 μL. In various embodiments, at least a portion of the reagent is transferred into the fluidic conduit to flush a portion of the collected sample into a chamber to form a sample mixture. 
     In various embodiments, a method as disclosed herein further comprises: flowing the sample streams through a flow sensor that is fluidly connected to the flow cell; measuring a sensing signal from the sample streams at the flow sensor to detect the entrance of the sample streams into the flow sensor and/or the exit of the sample streams out of the flow sensor; and using the reader instrument device to analyze the measured optical signal and sensing signal to determine the concentration of the target particles in the sample. 
     In various embodiments, a method as disclosed herein further comprises: flowing the sample streams through a flow sensor that is fluidly connected to the flow cell; measuring a sensing signal from the sample streams at the flow sensor to detect the sample streams entering and/or exiting the flow sensor; and using the reader instrument device to analyze the measured optical signal and sensing signal to determine the concentration of the target particles in the sample. In various embodiments, the sample streams in the flow cell and the flow sensor have the same flow rate. 
     In various embodiments, a method as disclosed herein further comprises: flowing the sample streams through a flow sensor that is fluidly connected to the flow cell; measuring a sensing signal from the sample streams at the flow sensor to quantify the volume of the sample streams; and using the reader instrument device to analyze the measured optical signal and sensing signal to determine the concentration of the target particles in the sample. In various embodiments, the sample streams in the flow cell and the flow sensor have the same flow rate. 
     In various embodiments, the optical signal and sensing signal are measured by the reader instrument device. 
     In various embodiments, the collected sample, reagent, sample mixtures, or sample streams are enclosed inside the cartridge device to prevent or limit their exposure to the environment outside the cartridge. 
     In various embodiments, the mixing step is performed in a fluidic structure. In various embodiments, the fluidic structure comprises one or a plurality of fluidic conduits. In various embodiments, the fluidic structure comprises one or a plurality of chambers. In various embodiments, each chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. In certain embodiments, the mixing step is performed in a fluidic structure comprising one or a plurality of chambers, and each chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. 
     In various embodiments, the fluidic structure is inside the cartridge device to prevent or limit exposing the sample, reagent, or sample mixtures to the environment outside the cartridge. In various embodiments, the flow cell is inside the cartridge device to prevent or limit exposing the sample streams to the environment outside the cartridge. In various embodiments, the flow sensor is inside the cartridge device to prevent or limit exposing the sample streams to the environment outside the cartridge. 
     In various embodiments, the flow cell has a width in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm. In various embodiments, the flow cell has a depth in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm. In various embodiments, the flow cell has a length in the range of about of 1-10 μm, 10-100 μm, 100-1,000 μm, 1,000-10,000 μm, or 10,000-50,000 μm. In various embodiments, the sample streams formed in the flow cell have a cross section of the same size as the flow cell. 
     In certain embodiments, the flow cell has a width in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm and a depth in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm; and the sample streams have a cross section of the same size as the flow cell. 
     In various embodiments, the sample streams in the flow cell have a flow rate in the range of 0.001-0.01, 0.01-0.1, 0.1-1, 1-50, 50-200, or 200-1000 μl/min when the optical signal is measured from the sample streams. In various embodiments, the optical signal measured from the sample streams at the flow cell comprises scattered light, reflected light, transmitted light, fluorescence, light absorption, light extinction, or white light image, or a combination thereof. 
     In various embodiments, the sample streams in the flow sensor have a flow rate in the range of 0.001-0.01, 0.01-0.1, 0.1-1, 1-50, 50-200, or 200-1000 μl/min when the sensing signal is measured from the sample streams. In various embodiments, the sensing signal measured from the sample streams at the flow sensor comprises an optical signal. In various embodiments, the optical signal comprises light transmission through and/or light reflection from the sample streams. 
     In various embodiments, the sample streams have the same flow rate in the flow cell and the flow sensor. 
     In various embodiments, the reagent comprises a fluorescent labeling agent that selectively labels the target particles in the sample with fluorescence, and wherein the optical signal from the sample streams comprises fluorescence. 
     In various embodiments, each of the sample streams is separately formed and measured in the flow cell. In various embodiments, at least two separate sample mixtures are transferred into the same flow cell to form at least two separate sample streams. In some embodiments, the at least two separate sample streams are formed consecutively (i.e., immediately one after another). In other embodiments, the at least two separate sample streams are formed nonconsecutively (i.e., not immediately one after another). In various embodiments, at least one sample stream comprises white blood cells as the target particles detected in the flow cell and at least another sample stream comprises red blood cells and/or platelet cells as the target particles detected in the flow cell. 
     In various embodiments, the fluidic channel in the flow sensor has a channel width in the range of about 0.001-0.05 mm, 0.05-1 mm, or 1-5 mm, and a channel depth in the range of about 0.001-0.01 mm, 0.01-0.5 mm, 0.5-1 mm, or 1-2 mm; and wherein the sample streams in the flow cell and the flow sensor have the same flow rate. 
     In certain embodiments, mixing is performed in at least one basic fluidic unit that comprises: a chamber configured to accommodate a fluid; a venting port connected to the chamber, wherein the venting port is connected to a pneumatic pressure source, an ambient pressure, or the atmosphere pressure; a microfluidic channel connected to the chamber; and a valve on the microfluidic channel. In various embodiments, the chamber of the basic fluidic unit has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2¬10 ml. In various embodiments, the microfluidic channel of the basic fluidic unit has a cross section of a size in the range of about 0.001-0.01 mm 2 , 0.01-0.1 mm 2 , 0.1-0.25 mm 2 , 0.25-0.5 mm 2 , 0.5-1 mm 2 , 1-2 mm 2 , or 2-10 mm 2 . 
     In certain embodiments, mixing is performed in at least one basic fluidic unit that comprises: a chamber configured to accommodate a fluid, wherein the chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml; a venting port connected to the chamber, wherein the venting port is connected to a pneumatic pressure source, an ambient pressure, or the atmosphere pressure; a microfluidic channel connected to the chamber, wherein the microfluidic channel has a cross section of a size in the range of about 0.001-0.01 mm 2 , 0.01-0.1 mm 2 , 0.1-0.25 mm 2 , 0.25-0.5 mm 2 , 0.5-1 mm 2 , 1¬2 mm 2 , or 2-10 mm 2 ; and a valve on the microfluidic channel. 
     In various embodiments, the sample mixtures are transferred from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device. In various embodiments, the external actuation mechanism comprises a pneumatic pressure source. In various embodiments, the external actuation mechanism is configured for forming the sample streams with a flow rate in the range of 0.001¬0.01, 0.01-0.1, 0.1-1, 1-50, 50-200, or 200-1000 μl/min. In certain embodiments, the sample mixtures are transferred from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device, and the external actuation mechanism comprises a pneumatic pressure source. 
     In various embodiments, the target particles have a size in the range of 0.1-1 μm, 1-10 μm, 10-15 μm, 15-30 μm, 30-50 μm, or 50-100 μm. In various embodiments, the target particles have a concentration in the range of 1-100, 100-1000, 1000-5000, 5000-20,000, or 20,000-50,000 target particles per μl sample steam. In certain embodiments, the target particles have a size in the range of 0.1-1 μm, 1-10 μm, 10-15 μm, 15-30 μm, 30-50 μm, or 50¬100 μm; and the target particles have a concentration in the range of 1-100, 100-1000, 1000¬5000, 5000-20,000, or 20,000-50,000 target particles per μl sample steam. 
     In various embodiments, the target particles comprise cells, plant cells, animal cells, blood cells, white blood cells, red blood cells, platelet cells, viruses, bacteria, fungi, yeasts, beads, fluorescent beads, or non-fluorescent beads; or other particles of proteins, enzymes, nucleic acids, polysaccharides, or polypeptides; or other particles bound with biological markers; or their combinations. 
       FIG. 1  illustrates one non-limiting example of the basic fluidic unit to be used in the cartridge. The basic fluidic unit  1001  has a chamber  1002 , a venting port  1003  and at least one microfluidic channel  1004  that accesses the chamber and has a valve  1005  on the microfluidic channel. The operation of basic fluidic unit  1001  depends on gravity or any other force serving as the replacement for gravity (e.g., centrifugal force) to keep fluid in position. Additionally, the basic fluidic unit  1001  uses another force such as pneumatic pressure to transfer fluid. More information regarding the design, operation, and manufacturing of fluid unit  1001  can be found in U.S. application Ser. No. 15/176,729 and PCT Application PCT/US16/36426, which are incorporated herein by reference in their entirety as if fully set forth. In some embodiments, the valve  1005  can be a passive valve. In other embodiments, the valve  1005  can be an active valve. In certain embodiments, the valve  1005  can be a hybrid or combination of passive and active valves. In other embodiments, the valve  1005  can be any design known to one of ordinary skill in the art. 
       FIGS. 2A-2D  illustrate a few non-limiting examples of passive valves. Other passive valve designs known to persons skilled in the art can also be used.  FIG. 2A  is a passive valve design having a channel with a hydrophilic inner surface and a patch of a hydrophobic surface.  FIG. 2B  is a passive valve design having a channel with a hydrophobic inner surface and a patch of a hydrophilic surface.  FIG. 2C  is a passive valve design having an enlargement of the channel cross-section along the flow direction and the channel has a hydrophilic surface.  FIG. 2D  is a passive valve design having a narrow down of the channel cross-section along the flow direction and the channel has a hydrophobic surface. 
       FIGS. 3A-3C  illustrate a few non-limiting examples of active valves. Other active valve designs known to persons skilled in the art can also be used.  FIG. 3A  shows a valve design that includes a flexible membrane  3001  and a substrate  3002 . When the flexible membrane  3001  is bent away from the substrate  3002 , the valve is in an “open” status to allow fluid flow to pass through. When the flexible membrane  3001  is bent towards the substrate  3002  leaving no gap, the valve is in the “close” status and fluid flow is not able to pass through.  FIG. 3B  shows a valve design that has a movable membrane  3003  and a substrate  3004 . When the movable membrane  3003  is away from the substrate  3004 , there is a fluid path  3005  between the inlet and outlet, and the valve is in “open” status. When the movable membrane is in proximity with the substrate leaving no gap, there is no fluid path between the inlet  3006  and the outlet  3007 , and the valve is in “close” status.  FIG. 3C  shows a valve design that has a plug  3008  on the channel. When the plug  3008  is pulled away from the channel leaving the substrate  3009 , the channel is in the “open” status allowing fluid flow from the inlet  3010  to the outlet  3011 . When the plug  3008  is inserted into the channel contacting the substrate  3009 , the channel is in the “close” status and there is no fluid path between the inlet  3010  and the outlet  3011 . The plug  3008  can be made of solid material, a polymer, an elastomer, a gel, a wax, a silicon oil, or other materials. When an active valve is used, an additional actuation mechanism can be used to operate the valve. 
       FIG. 4A  illustrates another non-limiting example of implementing a passive valve in a basic fluidic unit  4001 . In an embodiment, the transition area  4005  from the chamber  4002  to the channel  4004  provides a narrowing of the flow channel cross section. When both the channel inner surface and the chamber inner surface within this transition area  4005  are hydrophobic, as shown in  FIG. 4B , this transition area  4005  is equivalent to the sudden narrow down of a hydrophobic channel and acts as a passive valve to stop fluid in the chamber  4002  from entering the channel  4004 . When both the channel inner surface and the chamber inner surface within this transition area  4005  are hydrophilic, as shown in  FIG. 4C , this transition area is equivalent to the sudden enlargement of a hydrophobic channel and acts as a passive valve to stop fluid in the channel  4004  from entering the chamber  4002 . Additional designs of passive valves known to person skilled in the art can also be implemented. 
       FIG. 5  illustrates a symbol drawing that represents a basic fluidic unit as described herein, where the basic fluidic unit  5001  includes a chamber  5002 , a venting port  5003  and at least one microfluidic channel  5004  that accesses the chamber and has a valve  5005  on the microfluidic channel. The valve  5005  can be either a passive valve, an active valve or a hybrid or combination of both. In some embodiments, the basic fluidic unit  5001  can have one or a plurality of microfluidic channels (each having a valve) accessing the chamber  5002  (see, e.g., U.S. application Ser. No. 15/176,729 and PCT Application PCT/US16/36426, which are incorporated herein by reference in their entirety as if fully set forth). 
     In various embodiments, present disclosure provides fluidic cartridges having at least one basic fluidic unit as described herein. In various embodiments, the fluidic cartridges may have additional fluidic structures. One example of additional fluidic structure is one or more flow cells for a cytometer analysis. With conventional flow cytometers, the flow cell usually has a core diameter of several hundreds of micrometers. To achieve a sample stream of a smaller core diameter, e.g., a few to dozens of micrometers, the flow cell utilizes sheath flow to focus the sample stream. In some embodiments, a fluidic cartridge as described herein includes a conventional flow cell with sheath flow. 
     In other embodiments, a fluidic cartridge as described herein includes a sheathless flow cell instead of the conventional flow cell with sheath flow. The sheathless flow cell has a fluidic channel having a core diameter chosen according to the target sample stream diameter. For example, a fluidic channel having a diameter of 30 μm can be used to achieve a target sample stream having a diameter of 30 μm. Additionally, the channel of the flow cell can be transparent to certain excitation light and emission light wavelengths, so that optical signals can be measured from samples in the flow cell ( FIG. 6A ).  FIG. 6B  illustrates a symbolic drawing that represents a sheathless flow cell as described herein. Since the flow cell does not utilize sheath flow, the sample stream has a cross section in the same size as the flow cell. 
     Another example of an additional fluidic structures is one or a plurality of flow sensors for detecting the sample stream. Described herein are the design and operation of such a flow sensor, which has one or a plurality of sensing zones on a channel to detect the existence of liquid in the channel and/or measure the fluid displacement volume, the volume of a fluidic plug, flow rate or flow velocity, etc. More information regarding the design, operation and manufacturing of the flow sensor can be found in U.S. application Ser. No. 15/209,226 and PCT Application PCT/US16/42089, which are incorporated herein by reference in their entirety as if fully set forth.  FIG. 7A  illustrates one non-limiting example of the flow sensor, which has two sensing zones along the length of a fluidic channel. The sensor detects whether there is fluid inside the channel overlapping with the sensing zones. The volume of fluid filling up the channel between the two sensing zones can be determined by the known geometry of the channel.  FIG. 7B  is a symbolic drawing to represent this design.  FIG. 8A  illustrates another non-limiting example of the flow sensor, which has only one sensing zone along the length of a fluidic channel.  FIG. 8B  is a symbolic drawing to represent this design. 
     Described herein are various fluidic units and additional fluidic structures that can be used together in various configurations to achieve functions of a flow cytometer analysis integrating sample preparation and performing absolute count in a self-contained cartridge. 
       FIG. 9A  shows one exemplary configuration, where a basic fluidic unit  9001 , a sheathless flow cell  9007  and a flow sensor  9009  with two sensing zones  9011  and  9012  are connected in serial by fluidic conduits  9006  and  9008 . In some embodiments, the upstream end of the flow cell  9007  is connected to the microfluidic channel  9004  of the basic fluidic unit  9001 , and the downstream end of the flow cell  9007  is connected with the flow sensor. In this particular configuration, sample in the chamber  9002  of the unit  9001  will pass through the flow cell first and then through the flow sensor for a cytometer analysis. 
     When using this configuration for a cytometer analysis, as shown in  FIG. 9B , a fluid sample  9101  can first be loaded into the chamber  9002 . Pneumatic pressures can then be applied to the vent  9003  of the basic fluidic unit  9001  and to the outlet port  9010  of the flow sensor. When the pneumatic pressure at vent  9003  is higher than the pneumatic pressure at port  9010 , it creates a pressure difference that pumps sample  9101  from the chamber  9002  into the flow cell  9007  for the cytometer analysis, and then into the flow sensor  9009  for volume measurement. When the valve  9005  is a passive valve, a sufficiently-high pressure difference can pump the fluid sample to pass the valve  9005 . When the valve  9005  is an active valve, the valve  9005  can be switched to open status before the pressure can pump the fluid sample  9101  to pass the valve  9005 . 
     After applying the pneumatic pressures, data of the cytometer analysis in flow cell  9007  is continuously recorded. The recorded data includes the measured physical signal A (optical emission, electrical impedance, etc.) along time T as an array (A, T).  FIG. 9C  shows one example of the recorded data, where the amplitude of the signal A is plotted against the time T. The number of particles detected in the cytometer is determined by the number of peaks in the signal A. Meanwhile, as the sample continues to pass through the flow sensor  9009 , the time point T 1  of the sample reaching the first sensing zone  9011  is recorded, and the time point T 2  of the sample reaching the second zone  9012  is also recorded. The number of particles N detected between T 1  and T 2  can be determined from the record signal (A, T) as shown in the example of  FIG. 9C . The fluid volume V 0  for filling up the channel between the sensing zone  9011  and the sensing zone  9012  is a known parameter from the flow sensor design (see, e.g., U.S. application Ser. No. 15/209,226 and PCT Application PCT/US16/42089, which are incorporated herein by reference in their entirety as if fully set forth). Because the sheathless flow cell contains only the fluid sample for analysis (no sheath flow), the fluid volume between the two sensing zones can be used to determine the volume of sample analyzed in the flow cell  9007 . Therefore, the absolute count can then be calculated as: 
       Absolute Count= N/V   0   [1]
 
     In addition to the function of a cytometer analysis with absolute count, the example in  FIGS. 9A-9C  also has the feature that the whole fluidic structure can be implemented in a self-contained cartridge device. The cartridge device can be a molded piece of plastic with additional sealing layers. 
       FIG. 10A  shows another exemplary configuration, where a flow sensor  10007  is connected to the microfluidic channel  10004  of a basic fluidic unit  10001  with a fluidic conduit  10006 . Meanwhile, a sheathless flow cell  10009  is connected downstream of the flow sensor  10007  by a fluidic conduit  10008 . In this example, the number of cells counted N is determined by the signal (A, T) between time points T 1 +ΔT and T 2 +ΔT, as shown in  FIG. 10B , where ΔT can be any empirical value to compensate the time delay between the sample reaching the first sensing zone  10011  and sample reaching the flow cell  10009 . Like the operation of  FIG. 9A  discussed above, the configuration of  FIG. 10A  can also be used for a cytometer analysis with absolute count: 
       Absolute Count= N/V   0   [2]
 
       FIG. 11A  shows another exemplary configuration, where a basic fluidic unit  11001 , a sheathless flow cell  11007  and a flow sensor  11009  with one sensing zone  11012  are connected in serial by fluidic conduits  11006  and  11008 . In some embodiments, the upstream end of the flow cell is connected to the microfluidic channel  11004  of the basic fluidic unit  11001 , and the downstream end of the flow cell is connected to the flow sensor. In this exemplary configuration, sample in the chamber  11002  of the unit  11001  passes through the flow cell first and then through the flow sensor for a cytometer analysis. In this example, as shown in  FIG. 11B , the time points T 1 =0 (when the flow cell starts to detect particles) and T 2  (when the sample reaches the sensing zone  11012 ) are used to determine the total particle count N from the recorded signal (A, T). Additionally, the fluid volume V 1  to obtain the particle count N includes the total fluid conduit volume between the flow sensor  11007  and the sensing zone  11012  of the flow sensor  11009 . The fluid volume V 1  is a parameter known from the fluidic design. Like the operation of  FIG. 9  discussed above, the configuration of  FIG. 10  can also be used for cytometer analysis with absolute count: 
       Absolute Count= N/V   1   [3]
 
       FIG. 12A  shows another exemplary configuration, where two basic fluidic units  12101  and  12201  are used in serial with a sheathless flow cell  12301  and a flow sensor  12401 . A fluidic conduit  12001  connects the basic fluidic unit  12101 &#39;s microfluidic channel  12104  (having a valve  12105 ) with the basic fluidic unit  12201 &#39;s microfluidic channel  12204  (having a valve  12205 ). The unit  12201  has a second microfluidic channel  12206  (having a valve  12207 ), which connects to the upstream end of the flow cell  12301  by a fluid conduit  12002 . The downstream end of the flow cell  12301  is further connected to the flow sensor  12401  by a fluid conduit  12003 . In this example, the flow sensor  12401  has two sensing zones  12402  and  12403 . 
     For a cytometer analysis, pneumatic pressures are applied to three ports, including the vent  12103  of unit  12101  (P 1 ), the vent  12203  (P 2 ) of unit  12201 , and at the downstream port  12404  (P 3 ) of the flow sensor  12401 . By controlling the applied pneumatic pressures (P 1 , P 2 , and P 3 ), a fluid sample can be transferred between the chamber  12102  and the chamber  12202 , and further transferred into the flow cell for a cytometer analysis with the absolute count. 
     An exemplary method of controlling the pneumatic pressures (P 1 , P 2 , and P 3 ) and the corresponding fluid transfer is shown in the diagram of  FIG. 12B . When a fluid sample is in the first chamber (chamber  12102 ), by applying a pneumatic control (P 1 &gt;P 0  and P 2 =P 3 =P 0 ), the fluid sample can be transferred from the first chamber into the second chamber (chamber  12202 ). Similarly, by applying a pneumatic control (P 1 &lt;P 0  and P 2 =P 3 =P 0 ), the fluid sample can be transferred from the second chamber into the first chamber. When the fluid sample is in the second chamber, by applying a pneumatic control (P 1 =P 2 =P 0  and P 3 &lt;P 0 ), the fluid sample can be transferred from the second chamber into the flow cell and the flow sensor for the cytometer analysis. In this exemplary pneumatic control method, the vent port of the second chamber P 2  is kept at a constant pressure P 2 =P 0  during the operation. Following the teachings of this disclosure and the Applicants&#39; previous disclosures (see, e.g., U.S. application Ser. No. 15/176,729 and PCT Application PCT/US16/36426, which are incorporated herein by reference in their entirety as if fully set forth), other methods can also be used to control the fluid transfer in the configuration. For example, by applying a pneumatic control (P 1 =P 2 &gt;P 0  and P 3 =P 0 ), the fluid sample in the second chamber can be transferred from the second chamber into the flow cell and the flow sensor for the cytometer analysis. In certain embodiments, P 0  is the atmosphere pressure where the fluidic configuration is operated in. 
     With the pneumatic control method, a sample can be transferred in the fluidic configuration for the cytometer analysis with absolute count. For example, a fluid sample can be initially introduced into the first chamber (chamber  12102 ). The sample can then be transferred to the second chamber (chamber  12202 ). The sample can then be driven through the flow cell and the flow sensor for the cytometer analysis with absolute count as described above. In another example, the fluid sample be can initially introduced into the second chamber and next driven through the flow cell and the flow sensor for the cytometer analysis with absolute count. In yet another example, a fluid sample A can be initially introduced into the first chamber and a fluid sample B can be initially introduced to the second chamber, and then the two samples can be transferred between the two chambers for a plurality of mixing cycles, before being delivered to the flow cell for the cytometer analysis with the absolute count. This mixing action involves the fluid sample moving along one direction from the first chamber into the second chamber and then along an opposite direction from the second chamber into the first chamber, and vice versa. In some embodiments, the fluid sample A has a predetermined volume. In certain embodiments, the fluid sample B has a predetermined volume. 
     In another embodiment, a fluid sample A can be initially introduced to the first chamber  12102  and a fluid sample C can be initially loaded in the fluid conduit  12001 . By transferring the fluid sample between the two chambers, the fluid A and the fluid C can be mixed together, and then delivered to the flow cell for the cytometer analysis with the absolute count. The sample exiting the outlet of the flow sensor can be disposed or collected in a reservoir. In an embodiment where a reservoir is used to collect the exiting sample, the fluidic configuration of this example achieves the sample preparation, cytometer analysis and the absolute count function in a self-contained manner, without an exchange of fluid sample between the fluidic structure and the outside environment. Such an embodiment can be used for a cytometer analysis of different biological samples. For example, the fluid sample C can be a biological sample such as whole blood from human body. The fluid sample A can be a reagent containing a fluorophore-conjugated antibody targeting specific cell types, e.g., CD4+ lymphocytes, in the whole blood. By mixing these two fluids together and then measuring the mixture in the flow cell, it achieves the absolute count of the CD4+ Lymphocyte. In another example, the fluid sample C can be a human whole blood, whereas the fluid sample A can be a lysing solution selectively targeting Red Blood Cells (RBCs). After mixing the two fluids together and incubating the mixture for a period of time, the mixture is measured in the flow cell for a cytometer analysis such as the absolute count of the white blood cells (WBCs). 
       FIG. 12C  shows an exemplary fluidic configuration, where an additional fluid conduit  12004  is connected to the fluid conduit  12001  to introduce the initial sample C. The sample can be introduced via the port  12006  into the fluidic conduit  12001 . A valve  12005  can then be closed to seal the conduit  12004 , preventing the sample from exiting the port  12006 . In some embodiments, the fluid conduit  12001  can be used to collect a predetermined volume of the initial sample. In some embodiments, the valve  12005  can be a blood clotting valve (see, e.g., U.S. Pat. No. 8,845,979, which incorporated herein by reference in its entirety as if fully set forth). Other methods known to persons skilled in the art can also be used to introduce the initial samples. 
     In some embodiments, a reservoir chamber can be connected to outlet port of the flow sensor to collect the fluid sample after the cytometer analysis. As shown in the exemplary fluidic configuration of  FIG. 12D , a reservoir  12501  with a venting port  12502  can be connected to the outlet port  12404  of the flow sensor by a fluidic conduit  12503 . With this extra reservoir, the pneumatic pressure P 3  can be adjusted by controlling the pneumatic pressure P 4  at the venting port  12502  of the reservoir. An exemplary operation of this fluidic configuration is illustrated in  FIG. 12E . 
     In other embodiments, additional fluidic structures can be connected to one or more of the basic fluidic units, achieving additional operation functionalities.  FIG. 12F  shows one example of these embodiments. In comparison to the example of  FIG. 12A , the second basic fluidic unit  12201  has a third microfluidic channel  12208  (with a valve  12209 ), which connects by a fluidic conduit  12007  to a reservoir structure  12601  with a venting port  12602 . The venting port  12602  corresponds to a pneumatic pressure P 5 . A fluid sample D is initially stored in the reservoir  12601 .  FIG. 12G  shows a pneumatic control for operating this configuration. By applying a pneumatic control (P 5 &gt;P 0  and P 2 =P 0 ), the sample D initially stored in the reservoir  12601  is transferred into the second chamber  12202 . The rest of the pneumatic operation for the cytometer analysis can be the same as the example in the  FIG. 12B . 
     In yet another exemplary configuration, as shown in  FIG. 13A , there are three basic fluidic units  13101 ,  13201  and  13301 . The units  13101  and  13201  have microfluidic channels  13104  (with the valve  13105 ) and  13204  (with the valve  13205 ), respectively. The unit  13301  has three microfluidic channels  13304  (with the valve  13305 ),  13306  (with the valve  13307 ) and  13308  (with the valve  13309 ). A fluidic conduit  13001  connects the channels  13104  and  13304 , whereas another fluidic conduit  13002  connects the channel  13204  and  13306 . The fluid unit  13302  is also connected to an upstream port of a sheathless flow cell  13401  by a fluidic conduit  13003 , while the downstream port of the flow cell  13401  is connected to a flow sensor  13501  by a fluidic conduit  13004 . This fluidic configuration is operated by controlling the pneumatic pressures at the venting ports of the basic fluidic units  13103  (P 1 ),  13203  (P 2 ) and  13303  (P 3 ), and by controlling the pneumatic pressure of the outlet port  13504  of the flow sensor (P 4 ). 
     An exemplary method of controlling the pneumatic pressures (P 1 , P 2 , P 3  and P 4 ) and the corresponding fluid transfer is shown in the diagram of  FIG. 13B . A fluid sample in the first chamber ( 13102 ) can be transferred into the third chamber ( 13302 ) by applying a pneumatic control (P 1 &gt;P 0  and P 2 =P 3 =P 4 =P 0 ), whereas a fluid sample in the third chamber can be transferred into the first chamber by applying a pneumatic control (P 1 &lt;P 0  and P 2 =P 3 =P 4 =P 0 ). Similarly, a fluid sample in the second chamber ( 13202 ) can be transferred into the third chamber by applying a pneumatic control (P 2 &gt;P 0  and P 1 =P 3 =P 4 =P 0 ), whereas a fluid sample in the third chamber can be transferred into the second chamber by applying a pneumatic control (P 2 &lt;P 0  and P 1 =P 3 =P 4 =P 0 ). Meanwhile, a fluid sample in the third chamber can be transferred into the flow cell and the flow sensor for the cytometer analysis, by applying a pneumatic control (P 4 &lt;P 0  and P 1 =P 2 =P 3 =P 0 ). In this exemplary pneumatic control method, the vent port of the third chamber P 3  is kept at a constant pressure P 3 =P 0  during the operations. Following the teachings of this disclosure and Applicants&#39; previous disclosures (see, e.g., U.S. application Ser. No. 15/176,729 and PCT Application PCT/US16/36426, which are incorporated herein by reference in their entirety as if fully set forth), other methods can also be used to control the fluid transfer in this configuration. 
     This fluidic configuration and the fluid transfer diagram can be used to perform more complex sample preparation and cytometer analysis. For example, as shown in  FIG. 13C , a fluid sample A 1  is initially introduced into the first chamber and a fluid sample A 2  is initially introduced into the second chamber. Meanwhile, fluid samples B 1  and B 2  are each introduced into the fluidic conduit  13001  and  13002 , respectively. By applying the pneumatic control (P 1 &gt;P 0  and P 2 =P 3 =P 4 =P 0 ), the fluid samples A 1  and B 1  are transferred into the third chamber. By applying the pneumatic control (P 4 &lt;P 0  and P 1 =P 2 =P 3 =P 0 ), the sample mixture of A 1  and B 1  is transferred into the sheathless flow cell and the flow sensor for the cytometer analysis with the absolute count. After the cytometer analysis, if any residue of the sample mixture is left behind in the third chamber, it can be transferred back into the first chamber by applying pneumatic control (P 1 &lt;P 0  and P 2 =P 3 =P 4 =P 0 ) and thus make the third chamber empty to be ready for analysis of other samples. Prior to the cytometer analysis, if mixing uniformity of the sample mixture is a design consideration, the pneumatic control (P 1 &lt;P 0  and P 2 =P 3 =P 4 =P 0 ) and (P 1 &gt;P 0  and P 2 =P 3 =P 4 =P 0 ) can be applied in sequential to move the mixture from the third chamber into the first chamber, and then from the first chamber back into the third chamber again, introducing a mixing action of the sample. This step can be repeated to achieve desirable mixing uniformity. During these steps of fluid transfer, the fluid samples A 2  and B 2  do not move. This is achieved by keeping the pneumatic pressure (P 2 =P 3 ). Next, the fluid samples A 2  and B 2  can be transferred into the third chamber by applying the pneumatic control (P 2 &gt;P 0  and P 1 =P 3 =P 4 =P 0 ). The mixture of the samples A 2  and B 2  can be next transferred into the flow cell for the cytometer by applying the pneumatic control (P 4 &lt;P 0  and P 1 =P 2 =P 3 =P 0 ). If mixing uniformity is desirable, steps of repeated transfer between the second chamber and the third chamber can also be carried out similar to the repeated transfer steps between the first and the third chamber. In certain embodiments, the fluid sample A 1  has a predetermined volume. In certain embodiments, the fluid sample A 2  has predetermined volume. In certain embodiments, the fluid sample B 1  has predetermined volume. In certain embodiments, the fluid sample B 2  has predetermined volume. 
     This fluid configuration and the fluid transfer diagram can be used to implement a cytometer analysis of various biological samples. For example, the fluid sample A 1  can be a dilution buffer for RBC analysis and the sample B 1  can be whole blood, whereas the sample A 2  can be a lysing buffer for WBC analysis and the sample B 2  can be whole blood. A 1  and B 1  can be transferred into the third chamber to form a mixture, and then into the flow cell for counting and analyzing of RBCs and platelets in the blood. A 2  and B 2  can then be transferred into the third chamber to form a mixture, and then into the flow cell for counting and analyzing WBCs in the blood. Different dilution buffers and lysing buffers known to persons skilled in the art of hematology analyzers can be used. In this way, the fluid configuration can be used to achieve the Complete Blood Count (CBC) analysis widely used in clinical tests. 
       FIGS. 12A-12G  and  FIGS. 13A-13C  show examples having two and three basic fluidic units, respectively. In other embodiments, more basic fluidic units can be used in the configuration to achieve additional complexity. In the examples of  FIGS. 12A-12G  and  FIGS. 13A-13C , the fluidic conduits for connecting the basic fluidic units (e.g., the fluid conduit  12001 , the fluid conduit  13001  and the fluid conduit  13002 ) are fluid channels. In other embodiments, fluid structures with additional complexity can be used as the fluidic conduits. 
       FIG. 14A  shows an example with four basic fluidic units,  14101 ,  14201 ,  14301  and  14401 . Each of the four units  14010 ,  14201  and  14401  has a microfluidic channel with a valve. The unit  14301  has four microfluidic channels including channel  14304  (with valve  14305 ), channel  14306  (with valve  14307 ), channel  14308  (with valve  14309 ), and channel  14310  (with valve  14311 ). The basic fluidic unit  14101  is connected to the basic fluidic unit  14301  by a fluidic conduit  14001 . The basic fluidic unit  14201  is connected to the basic fluidic unit  14301  by a fluidic conduit  14002 . The basic fluidic unit  14401  is connected to the basic fluidic unit  14301  by a fluidic conduit  14003 . The upstream of a sheathless flow cell  14501  is connected to the basic fluidic unit  14301  by a fluidic conduit  14004 , while the downstream of the flow cell  14501  is connected by a fluidic conduit  14005  to a flow sensor  14601  that has two sensing zones  14602  and  14603 . The flow sensor  14601  is then connected to a reservoir chamber  14701  that has a venting port  14702 . Meanwhile, a sample A 1  can be initially stored in the chamber  14102  of the basic fluidic unit  14101 , a sample A 2  can be initially stored in the chamber  14202  of the basic fluidic unit  14201  and a sample A 3  can be initially stored in the chamber  14402  of the basic fluidic unit  14401 . Additionally, a sample B 1  can be induced into the fluidic conduit  14001  by an inlet port  14801  through a fluidic conduit  14801  with a valve  14803 . The valve  14803  can be closed after inducing the sample. In some embodiments, the fluidic conduit  14001  can be used to collect a predetermined volume of the sample. Similarly, a sample B 2  can be induced into the fluidic conduit  14002  by an inlet port  14901  through a fluidic conduit  14902  with a valve  14903 . The valve  14903  can be closed after inducing the sample. In some embodiments, the fluidic conduit  14002  can be used to collect a predetermined volume of the sample. 
     An exemplary method of controlling the pneumatic pressures (P 1 , P 2 , P 3 , P 4  and P 5 ) is described below and the corresponding fluid transfer is shown in the diagram of  FIG. 14B . The pneumatic pressure P 5  at the venting port  14702  of the reservoir  14701  balances with the pressure P 5 ′ at the downstream port  14604  of the flow sensor  14601 , when there is a pneumatic path between these two ports (e.g., when there is air path in the reservoir  14701  to balance the venting port  14702  and the port  14604 ). A fluid sample in the first chamber ( 14102 ) can be transferred into the third chamber ( 14302 ) by applying a pneumatic control (P 1 &gt;P 0  and P 2 =P 3 =P 4 =P 5 =P 0 ), whereas a fluid sample in the third chamber can be transferred into the first chamber by applying a pneumatic control (P 1 &gt;P 0  and P 2 =P 3 =P 4 =P 5 =P 0  where P 0  is the atmosphere pressure. A fluid sample in the second chamber ( 14202 ) can be transferred into the third chamber by applying a pneumatic control (P 2 &gt;P 0  and P 1 =P 3 =P 4 =P 5 =P 0 ), whereas a fluid sample in the third chamber can be transferred into the second chamber by applying a pneumatic control (P 2 &lt;P 0  and P 1 =P 3 =P 4 =P 5 =P 0 ). Similarly, a fluid sample in the fourth chamber ( 14402 ) can be transferred into the third chamber by applying a pneumatic control (P 4 &gt;P 0  and P 1 =P 2 =P 3 =P 5 =P 0 ), whereas a fluid sample in the third chamber can be transferred into the fourth chamber by applying a pneumatic control (P 4 &lt;P 0  and P 1 =P 2 =P 3 =P 5 =P 0 ). Meanwhile, a fluid sample in the third chamber can be transferred into the flow cell and the flow sensor for the cytometer analysis, by applying a pneumatic control (P 5 &lt;P 0  and P 1 =P 2 =P 3 =P 4 =P 0 ). In this exemplary pneumatic control method, the vent port of the third chamber P 3  is kept at a constant pressure P 3 =P 0  during the operations. Following the teachings of this disclosure and Applicants&#39; previous disclosures (see, e.g., U.S. application Ser. No. 15/176,729 and PCT Application PCT/US16/36426, which are incorporated herein by reference in their entirety as if fully set forth), other methods can also be used to control the fluid transfer in this configuration. 
     In various embodiments, the sheathless flow cell is where the target particles in a fluid sample flow are detected and measured by different signals such as fluorescence, light scattering, light absorption, and light extinction, white light imaging, etc. An excitation light (EL) beam from a light source can be shaped and used to illuminate a designated sensing area of the flow cell and trigger the above signals from the target particles. 
     The sheathless flow cell can be a fluidic channel that has various geometry shapes.  FIGS. 15A-15D  show the top view (in x-y plane) of a few examples of the flow cell. The top view (x-y plane) is defined as the plane perpendicular to the direction of the excitation light (z-axis). The length is defined the as channel dimension along the sample flow (x-axis), and the width is defined as the dimension along the y-axis. The depth is defined as the channel dimension along the z-axis.  FIG. 15B  shows an example of a flow cell that has a gradually decreased width, where the maximum width is W 1  and the minimum width is W 2 . In other embodiments, the flow cell can have a gradually increased width.  FIG. 15C  shows an example of a flow cell that has a non-gradually changing width, where the maximum width is W 1  and the minimum width is W 2 .  FIG. 15D  shows an example of a flow cell that has a fixed width (W 1 =W 2 =W 0 ) at various positions along channel length. In some embodiments, the difference of the maximum width W 1  and the minimum width W 2  are within a designated difference. A non-limiting example of the range of the width difference is (W 1 −W 2 )/W 2 ≤20%. The ranges of the channel width and the depth are chosen to be large enough so that target particles (e.g., cells in biological samples), can pass through the flow cell without blocking it. Meanwhile, they are chosen to be small enough to minimize the coincidence error in the flow cytometer analysis. The minimum width W 1  can be in the range of 1-10 μm, 10-40 μm, 40 to 100 μm, or 100 to 200 μm. The depth of the channel can be in the range of 1-10 μm, 10-40 μm, 40 to 100 μm, or 100 to 200 μm. The cross section of the channel (in y-z plane) can have the shape of a rectangular, a trapezoid, a circle, a half circle, or any other shapes. The length of the flow cell should be long enough for the optical detection of particles in the sample stream, and meanwhile, short enough to reduce the flow resistance of the sample stream flowing through. In various embodiments, the length of the flow cell can be in the range of about 1-10 μm, 10-100 μm, 100-1,000 μm, 1,000-10,000 μm, or 10,000-50,000 μm. 
     As the sheathless flow cell is used for optical measurement, at least one surface of the channel is transparent to the light wavelength involved in the measurement. The material for forming the channel surface can be any transparent material such as glass, quartz, and plastics including, but not limited to, Cyclic Olefin Copolymer (COC), Cyclo-olefin Polymer (COP), Poly-Methyl methacrylate (PMMA), polycarbonate (PC), Polystyrene (PS), and Poly-chloro-tri-fluoro-ethylene (PCTFE) materials such as Aclar, etc. 
     The fluid sample for analysis in the flow cell can be a fluid suspension of a plurality of particles. For example, the fluid sample can be a blood sample containing different cells such as white blood cells, red blood cells and platelets. In another example, the fluidic sample can be a blood sample, in which certain types of cells remain intact, such as white blood cells, while other types of cells have been lysed, such as red blood cells. In another example, the fluid sample can be a blood sample in which certain types of cells have been labeled with a fluorophore. In another example, the fluidic sample can be a mixture of the cells and other particles, such as non-fluorescent beads and/or fluorescent beads. In other examples, the fluid samples can also be other biological samples such as cerebrospinal fluid, urine, saliva, semen, etc. 
     When particles flow through the sheathless flow cell, various optical signals can be measured to detect and characterize the particles. The measurable signals include, but are not limited to, fluorescence, light scattering, light absorption, light distinction, etc.  FIG. 16A  shows an example where a plurality of particles flow through the flow cell for detection. All particles in the sample flow through in a one-by-one manner. Under the illumination of the excitation light (EL), each cell can be characterized for optical signals that include but are not limited to fluorescence (FL) and light scattering (LS).  FIG. 16B  shows another example where a plurality of particles flow through the flow cell for detection. Some particles are flowing through while overlapping with each other. Nevertheless, if only considering the target particles, they are flowing through still in a one-by-one manner without overlapping with other target particles. In this case, the light scattering from the target particles may be blocked by other particles overlapping with them. Nevertheless, other signals that include but are not limited to fluorescence signal can still be measured to detect these target particles if these particles are treated with specific fluorophore to distinguish from the other particles beforehand. In some embodiments, the other particles can be non-fluorescent or treated with different fluorophore distinguishable from the target particles. 
     In an embodiment, the fluid sample can be a blood sample in which the white blood cells are labeled with fluorophore and the red blood cells are not labeled with fluorophore. When the labeled white blood cells pass through the flow cell one-by-one, the corresponding fluorescence signal can be measured to detect and characterize the white blood cell even when there are red blood cells overlapping with them. In another embodiment, the fluid sample can be a blood sample in which the white blood cells are labeled with fluorophore and the red blood cells are lysed. When the labeled white blood cells pass through the flow cell one-by-one, the corresponding fluorescence signal and light scattering signals can be measured simultaneously from these cells for detection and characterization. In another embodiment, the fluid sample can be a blood sample in which there are fluorophore-labeled white blood cells and fluorescent beads. When these white blood cells and the beads pass through the flow cell one-by-one, they can be detected by the corresponding fluorescence signal. Other cells having no fluorescence, or a different wavelength of fluorescence do not impede the measurement. In another embodiment, the fluid sample can be a blood sample in which there are red blood cells and beads among other cells. When the cells pass through one-by-one, light scattering signals can be measured to detect and characterize the red blood cells and the beads. In yet other embodiment, the bead can be label with a fluorophore, so they can be distinguished from the red blood cells by the light scattering signals or by fluorescence signals, or by both signals. 
     A combination of the sheathless flow cell and the flow sensor achieves the desired functionality of the cytometer analysis with the absolute count of particles.  FIG. 17A  shows one exemplary design, where the outlet  17103  of the flow cell  17101  is coupled to the inlet  17202  of the flow sensor  17201  by a fluidic conduit  17001 . In certain embodiments, the outlet of the flow cell  17101  can be coupled to the inlet  17202  of the flow sensor  17201  directly and without additional fluidic conduit. The flow sensor  17201  has two sensing zones  17204  and  17205 . A fluid sample flows into the inlet  17102  of the flow cell  17101  and then out of the outlet  17203  of the flow sensor  17201 . The signal measured in the flow cell  17101  is recorded, as illustrated in  FIG. 17B . Time T 0  is when the sample starts being detected in the flow cell  17101 , T 1  is when the fluid sample passes the sensing zone  17204 , and T 2  is when the fluid sample passes the sensing zone  17205 . From time T 1  to T 2 , the total number of target particles detected in the flow cell  17101  is N. The fluid volume V 0  between the two sensing zones  17204 ,  17205  is a known parameter from the design of the flow sensor. Because the flow cell  17101  has a sheathless design, the volume of fluid flows through the flow cell  17101  is only the fluid sample. Therefore, the sample volume being measured in the flow cell  17101  between T 1  and T 2  equals to V 0 . In this design, the absolute count is determined as: 
       Absolute Count 1 =N/V   0   [4]
 
       FIG. 17C  shows another exemplary design, where the flow sensor  17201  has only one sensing zone  17205 .  FIG. 17D  is the signal measured from this design, where time T 0  is when the sample starts being detected in the flow cell, and T 2  is when the fluid sample passes the sensing zone  17205 . From time T 0  to T 2 , the total number of target particles detected in the flow cell is N′. The volume V 0 ′ is the total fluid volume filling up the fluidic conduit from the flow cell  17101  to the sensing zone  17205 . In this design, the absolute count is determined as: 
       Absolute Count 2 =N′/V   0 ′  [5]
 
       FIG. 18A  shows another exemplary design, where the inlet  18102  of the flow cell  18101  is coupled to the outlet  18203  of the flow sensor  18201  by a fluidic conduit  18001 . The flow sensor  18201  has two sensing zones  18204  and  18205 . A fluid sample flows into the inlet  18102  of the flow sensor  18201  and then out of the outlet  18203  of the flow sensor  18201 . The signal measured in the flow cell  18101  is recorded, as illustrated in  FIG. 18B . T 1  is when the fluid sample passes the sensing zone  18204 , and T 2  is when the fluid sample passes the sensing zone  18205 . In this example, the number of cells counted N″ is determined by the signal (A, T) between time points T 1 +ΔT and T 2 +ΔT, as shown in  FIG. 18B , where ΔT can be any empirical value to compensate the time delay between sample reaching the first sensing zone  18204  and sample reaching the flow cell  18101 . From time T 1 +ΔT to T 2 +ΔT, the total number of target particles detected in the flow cell is N″. The fluid volume V 0  between the two sensing zones  18204 ,  18205  is a known parameter from the design of the flow sensor  18201 . In this design, the absolute count is determined as: 
       Absolute Count 3 =N″/V   0   [6]
 
     This combination of the flow cell  18101  and the flow sensor  18201  can be used for measurement of particles or cells. The size of the target particles can be in the range of 0.1-1 μm, 1-10 μm, 10-15 μm, 15-30 μm, 30-50 μm, or 50-100 μm depending on the size of the flow cell  18101 . To minimize the risk of clogging the sheathless channel, the size of the particles being measured should be smaller than size of the flow cell  18101 , and the size difference can range from 1-5 μm, 5-10 μm, 10-20 μm, or 20-50 μm. To minimize the coincidence error for the cytometer analysis, the concentration of the target particles in the fluid sample can be in the range of 1-100, 100-1000, 1000-5000, 5000-20,000, or 20,000-50,000 particles or cells per μl sample. 
     When the target particles are biological cells, too fast of a flow velocity in the sheathless flow cell can introduce shear force and may lyse the cells. Because the sheathless flow cell has a dimension similar to the target particles, this imposes a limitation on the flow rate of the sample. The flow rate can be in the range of 0.001-1, 1-50, 50-200, or 200-1000 microliters per minute (μ1/min). In certain embodiments, the ranges can be 1-50 or 50-200 μl/min. For size consideration when implementing in self-contained cartridges, the range of the fluid sample volume can be constrained by the cartridge size. The volume of the flow sensor and the total volume of the sample can be in the range of 0.1-1 μl, 1-200 μl, 200-1000 μl, 1-5 ml, or 5-30 ml. In certain embodiments, the range can be 1-200 μl, 200-1000 μl l or 1-5 ml. In certain embodiments, by considering both the sample volume and the flow rate, the measurement is completed in less than 10 minutes. 
     By further incorporating the combination of the sheathless flow cell and the flow sensor with the basic fluidic unit, as illustrated in the examples shown in  FIGS. 9A-14B , sample preparation steps can be further integrated with the cytometer analysis including the absolute count. The integration of the above functions enables the fluidic configurations to be operated as a self-contained structure for a cytometer analysis, without fluid exchange with the outside environment after the fluid samples having been loaded into the cartridge. 
     In different embodiments of the fluidic configurations, pneumatic pressures are applied to the venting ports of the basic fluidic units and additional venting ports of other fluidic structures such as a reservoir (see, e.g.,  FIG. 12D  and  FIG. 14A ). The higher the pressure difference between two venting ports is, the higher the flow rate to transfer fluid in the microfluidic channels. When the fluid sample is a biological sample containing cells, a high flow rate in a confined channel may induce a large shear force to lyse the cells. Considering this limitation, the pressure difference between any two of the applied pressures can be in the range of 0-1, 1-5, 5-15, or 15-30 psi. In certain embodiments, the range can be 0-1, 1-5, or 5-15 psi. In certain embodiments, at least one of the venting ports can be connected to the atmosphere pressure of the environment. When at least one venting port is connected to the atmosphere pressure, another pressure higher than the atmosphere pressure applied introduces a positive pressure difference in comparison to the atmosphere pressure. This positive pressure difference can be in the range of 0-1, 1-5, 5-15, or 15-30 psi. In certain embodiments, the range can be 0-1, 1-5, or 5-15 psi. When at least one venting port is connected to the atmosphere pressure, another pressure lower than the atmosphere pressure applied introduces a negative pressure difference. This negative pressure difference can be in a range of 0-1, 1-5, 5-15, or 15-30 psi. In certain embodiments, the range can be 0-1, 1-5, or 5-15 psi. The flow rate achieved for transferring the sample via the channel between any two of the basic fluidic units can be in the range of 0-1, 1-50, 50-200, or 200-1000 μl/min, or 1-10 ml/min. In certain embodiments, the range can be 1 microliter to 1-50, 50-200, or 200-1000 μl/min. 
     Various fluidic configurations incorporating a plurality of basic fluidic units and a plurality of the combinations of the sheathless flow cell and the flow sensor can be implemented in various manufacturing structures to form a fluidic cartridge. In some embodiments, this cartridge can be inserted into a reader instrument for operation, as shown in the example of  FIG. 19 . The cartridge  19101  having the fluidic structure  19102  can be inserted into a docking slot  19202  on the reader instrument  19201 . In some embodiments, a control unit of the reader instrument records the signals from the cytometer analysis. Some examples of the signals include but are not limited to the optical signals such as fluorescence, light scattering, light absorption, etc. In some embodiments, the reader instrument has alignment mechanisms and features to align the sheathless flow cell with the optics in the instrument for optical signal measurement. In some embodiments, the control unit of the reader instrument also detects the signals from the flow sensor to determine the absolute count. In some embodiments, the control unit of the reader instrument also applies the pneumatic pressure source to the cartridges to drive the fluid transfer. In some embodiments, the control unit of the reader instrument also supports additional actuations such as opening or closing a valve structure in the cartridge fluidics. In some embodiments, the cartridge is self-contained and there is no exchange of liquid samples between the cartridge and the reader instrument. In some embodiments, the cartridge is not self-contained, and the reader instrument has on-board liquid storage and there is liquid exchange between the reader instrument and the cartridge, such as liquid infusion from the reader instrument into the cartridge. 
     In some embodiments, the cartridge stays stationary after being inserted into the reader, whereas the interface for external connections such as the pneumatic pressure source moves to make contact with the cartridge. In other embodiments, the cartridge can be movable after being inserted into the reader and is moved to make contact with the interface for external connections such as pneumatic pressure sources. 
     The sheathless flow cell in the fluidic structures can be built with various manufacturing processes. In some embodiments, an open fluidic channel for the flow cell can be built by injection molding, embossing, etching, CNC, laser cutting, or die cutting, etc. A cover can then be added onto the patterns to form enclosed fluidic channel to be the flow cell. The cover can be added by various manufacturing process, such as thermal fusion bonding, thermal lamination, adhesive bonding, solvent assisted bonding, laser wielding, and ultrasonic wielding, etc. Non-limiting examples of building the sheathless flow cell are described here. In some embodiments, optical signals are detected from particles flowing inside the sheathless flow cell. Smooth surface of the flow cell is useful to achieve acceptable optical signals.  FIG. 20A  shows one example of the sheathless flow cell  20101  having two pieces. The cross-section view (y-z plane) is perpendicular to the direction of sample flow (x-axis). The bottom piece  20102  forms three sides of a channel without a cover. The top piece  20103  adds a cover side to the channel, which then forms an enclosed channel. The bottom and the top surfaces  20104  and  20105  can achieve smoothness for optical measurement in the two pieces  20102  and  20103 , respectively.  FIG. 20B  shows another example of building the sheathless flow cell  20201  having three pieces. The middle piece  20202  forms two sides of a channel, without top and bottom sides. Then a bottom piece  20203  and a top piece  20204  are added separately. The three pieces together forms an enclosed channel as the flow cell. The surface  20205  and  20206  can achieve smoothness for optical measurement in the two pieces  20203  and  20204 , respectively. 
     The cartridge device for the cytometer analysis can be of any size. In certain embodiment, the cartridge device is received in the reader instrument device for the measurement and analysis and has a size in the range of about 0.1-1 cm 3 , 1-5 cm 3 , 5-25 cm 3 , 25¬50 cm 3 , or 50-200 cm 3 . 
     Many variations and alternative elements have been disclosed in embodiments of the present disclosure. Still further variations and alternate elements will be apparent to one of skill in the art. Among these variations, without limitation, are the selection of fluidic units, components and structures for the inventive devices and methods, and the samples that may be analyzed therewith. Various embodiments of the disclosure can specifically include or exclude any of these variations or elements. 
     In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the disclosure are to be understood as being modified in some instances by the term “about.” As one non-limiting example, one of ordinary skill in the art would generally consider a value difference (increase or decrease) no more than 10% to be in the meaning of the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the disclosure may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. 
     Groupings of alternative elements or embodiments of the disclosure disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims. 
     The disclosure is explained by various examples, which are intended to be purely exemplary of the disclosure and should not be considered as limiting the disclosure in any way. Various examples are provided to better illustrate the claimed disclosure and are not to be interpreted as limiting the scope of the disclosure. To the extent that specific materials are mentioned, it is merely for purposes of illustration and is not intended to limit the disclosure. One skilled in the art may develop equivalent means or reactants without the exercise of inventive capacity and without departing from the scope of the disclosure. 
     The various methods and techniques described above provide a number of ways to carry out the application. Of course, it is to be understood that not necessarily all objectives or advantages described can be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that the methods can be performed in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objectives or advantages as taught or suggested herein. A variety of alternatives are mentioned herein. It is to be understood that some preferred embodiments specifically include one, another, or several features, while others specifically exclude one, another, or several features, while still others mitigate a particular feature by inclusion of one, another, or several advantageous features. 
     Furthermore, the skilled artisan will recognize the applicability of various features from different embodiments. Similarly, the various elements, features and steps discussed above, as well as other known equivalents for each such element, feature, or step, can be employed in various combinations by one of ordinary skill in this art to perform methods in accordance with the principles described herein. Among the various elements, features, and steps some will be specifically included, and others specifically excluded in diverse embodiments. 
     Although the application has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the embodiments of the application extend beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and modifications and equivalents thereof. 
     Preferred embodiments of this application are described herein, including the best mode known to the inventors for carrying out the application. Variations on those preferred embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. It is contemplated that skilled artisans can employ such variations as appropriate, and the application can be practiced otherwise than specifically described herein. Accordingly, many embodiments of this application include all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the application unless otherwise indicated herein or otherwise clearly contradicted by context. 
     All patents, patent applications, publications of patent applications, and other material, such as articles, books, specifications, publications, documents, things, and/or the like, referenced herein are hereby incorporated herein by this reference in their entirety for all purposes, excepting any prosecution file history associated with same, any of same that is inconsistent with or in conflict with the present document, or any of same that may have a limiting affect as to the broadest scope of the claims now or later associated with the present document. By way of example, should there be any inconsistency or conflict between the description, definition, and/or the use of a term associated with any of the incorporated material and that associated with the present document, the description, definition, and/or the use of the term in the present document shall prevail. 
     It is to be understood that the embodiments of the application disclosed herein are illustrative of the principles of the embodiments of the application. Other modifications that can be employed can be within the scope of the application. Thus, by way of example, but not of limitation, alternative configurations of the embodiments of the application can be utilized in accordance with the teachings herein. Accordingly, embodiments of the present application are not limited to that precisely as shown and described. 
     Various embodiments of the disclosure are described above in the Detailed Description. While these descriptions directly describe the above embodiments, it is understood that those skilled in the art may conceive modifications and/or variations to the specific embodiments shown and described herein. Any such modifications or variations that fall within the purview of this description are intended to be included therein as well. Unless specifically noted, it is the intention of the inventors that the words and phrases in the specification and claims be given the ordinary and accustomed meanings to those of ordinary skill in the applicable art(s). 
     The foregoing description of various embodiments of the disclosure known to the applicant at this time of filing the application has been presented and is intended for the purposes of illustration and description. The present description is not intended to be exhaustive nor limit the disclosure to the precise form disclosed and many modifications and variations are possible in the light of the above teachings. The embodiments described serve to explain the principles of the disclosure and its practical application and to enable others skilled in the art to utilize the disclosure in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed for carrying out the disclosure. 
     While particular embodiments of the present disclosure have been shown and described, it will be obvious to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from this disclosure and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of this disclosure. 
     Additional Aspects of the Present Disclosure 
     Aspects of the subject matter described herein may be useful alone or in combination with any one or more of the other aspect described herein. Without limiting the foregoing description, in a first aspect of the present disclosure, a device for analyzing target particles in a sample includes a cartridge device, wherein the cartridge device comprises: an inlet configured for receiving the sample into the cartridge device; a fluidic structure fluidly connected to the inlet and configured for mixing at least a portion of the sample with at least a portion of a reagent to form one or more sample mixtures; a flow cell fluidly connected to the fluidic structure and configured for forming one or more sample streams from the one or more sample mixtures, wherein the sample streams are formed in the flow cell without a sheath flow, and wherein the flow cell comprises an optically transparent area configured for measuring an optical signal from the sample streams to detect the target particles in the sample; and a flow sensor fluidly connected to the flow cell and configured for measuring a sensing signal from the sample streams that enter the flow sensor. 
     In accordance with a second aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic structure comprises one or a plurality of chambers, wherein each chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml; and wherein the fluidic structure is configured for transferring the sample mixtures from one of the chambers to the flow cell to form the sample streams. 
     In accordance with a third aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the flow cell has a width in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm and a depth in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm; and wherein the sample streams have a cross section of the same size as the flow cell. 
     In accordance with a fourth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the flow cell has a length in the range of about of 1-10 μm, 10-100 μm, 100-1,000 μm, 1,000-10,000 μm, or 10,000-50,000 μm. 
     In accordance with a fifth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the optically transparent area on the flow cell has a transmission rate of 50-60%, 60-70%, 70-80%, 80-90%, 90-96%, or 96-99.9% for the optical signal from the sample streams, and wherein the optical signal comprises scattered light, reflected light, transmitted light, fluorescence, light absorption, light extinction, or white light image, or a combination thereof. 
     In accordance with a sixth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the optically transparent area on the flow cell is made of a plastic material. 
     In accordance with a seventh aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the cartridge device further comprises a reagent. 
     In accordance with an eighth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the reagent comprises a fluorescent labeling agent that selectively labels the target particles in the sample with fluorescence, and wherein the optical signal from the sample streams comprises fluorescence. 
     In accordance with a ninth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the flow sensor comprises a fluidic channel and a sensing zone on the fluidic channel, wherein the fluidic channel is fluidly connected to the flow cell to allow the sample streams to flow through; and wherein a sensing signal is measured when the sample streams enter the sensing zone. 
     In accordance with a tenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic channel in the flow sensor has a channel width in the range of about 0.001-0.05 mm, 0.05-1 mm, or 1-5 mm, and a channel depth in the range of about 0.001-0.01 mm, 0.01-0.5 mm, 0.5-1 mm, or 1-2 mm. 
     In accordance with an eleventh aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the sensing zone comprises an optically transparent area configured for measuring an optical signal that changes levels between the absence and presence of the sample streams in the sensing zone. 
     In accordance with a twelfth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic connection between the flow cell and the flow sensor is configured for a sample stream to have the same flow rate flowing through the flow cell and the flow sensor. 
     In accordance with a thirteenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic structure comprises at least one basic fluidic unit that comprises: a chamber configured to accommodate a fluid; a venting port connected to the chamber, wherein the venting port is connected to a pneumatic pressure source, an ambient pressure, or the atmosphere pressure; a microfluidic channel connected to the chamber; and a valve on the microfluidic channel. 
     In accordance with a fourteenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml, and wherein the microfluidic channel has a cross section of a size in the range of about 0.001-0.01 mm2, 0.01-0.1 mm2, 0.1-0.25 mm2, 0.25-0.5 mm2, 0.5-1 mm2, 1-2 mm2, or 2-10 mm2. 
     In accordance with a fifteenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the cartridge device is configured for transferring the sample mixtures from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device, and wherein the external actuation mechanism comprises a pneumatic pressure source. 
     In accordance with a sixteenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, when the cartridge device is in use, the chamber is so positioned that the at least a portion of the fluid inside the chamber is pulled by gravity towards the microfluidic channel and/or away from the venting port. 
     In accordance with a seventeenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, when the cartridge device is in use, the chamber has a volume larger than the volume of the fluid accommodated therein and an air gap exists between the venting port and the fluid accommodated therein. 
     In accordance with an eighteenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the valve is a passive valve that is configured for allowing a fluid flow to pass through the microfluidic channel when a pneumatic pressure is applied to the fluid flow and stopping the fluid flow when no pneumatic pressure is applied to the fluid flow. 
     In accordance with a nineteenth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the valve is a passive valve that comprises one of the following structures: (i) a channel with a hydrophilic inner surface embedded with a patch of a hydrophobic surface, (ii) a channel with a hydrophobic inner surface embedded with a patch of a hydrophilic surface, (iii) an enlargement of the channel cross section along the flow direction in a channel with a hydrophilic inner surface, and (iv) a contraction of the channel cross section along the flow direction in a channel with a hydrophobic inner surface. 
     In accordance with a twentieth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the device further comprises a reader instrument device, wherein the reader instrument device is configured for receiving, operating, and/or actuating the cartridge device. 
     In accordance with a twenty-first aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the reader instrument device is configured for measuring the optical signal at the flow cell to quantify the target particles in the sample. 
     In accordance with a twenty-second aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the reader instrument device is configured for measuring the optical signal at the flow cell and the sensing signal at the flow sensor to determine the concentration of the target particles in the sample. 
     In accordance with a twenty-third aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, a method for analyzing target particles in a sample includes applying the sample to a cartridge device, which is configured for collecting a predetermined sample volume into the cartridge device; transferring the cartridge device into a reader instrument device; mixing at least a portion of the collected sample and at least a portion of a reagent to form one or more sample mixtures inside the cartridge device; forming one or more sample streams from the one or more sample mixtures in a flow cell inside the cartridge device, wherein the sample streams are formed in the flow cell without a sheath flow; measuring an optical signal from the sample streams at the flow cell to detect the target particles in the sample streams; and using the reader instrument device to analyze the measured optical signal to quantify the target particles in the sample. 
     In accordance with a twenty-fourth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the method includes flowing the sample streams through a flow sensor that is fluidly connected to the flow cell; measuring a sensing signal from the sample streams at the flow sensor to detect the entrance of the sample streams into the flow sensor and/or the exit of the sample streams out of the flow sensor; and using the reader instrument device to analyze the measured optical signal and sensing signal to determine the concentration of the target particles in the sample. 
     In accordance with a twenty-fifth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the target particles have a size in the range of 0.1-1 μm, 1-10 μm, 10-15 μm, 15-30 μm, 30-50 μm, or 50¬100 μm; and wherein the target particles have a concentration in the range of 1-100, 100-1000, 1000-5000, 5000-20,000, or 20,000-50,000 target particles per μl sample steam. 
     In accordance with a twenty-sixth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the reagent comprises a fluorescent labeling agent that selectively labels the target particles in the sample with fluorescence, and wherein the optical signal from the sample streams comprises fluorescence. 
     In accordance with a twenty-seventh aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the mixing step is performed in a fluidic structure comprising one or a plurality of chambers, wherein each chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. 
     In accordance with a twenty-eighth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the flow cell has a width in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm and a depth in the range of about 1-10 μm, 10-40 μm, 40-100 μm, or 100-200 μm; and wherein the sample streams have a cross section of the same size as the flow cell. 
     In accordance with a twenty-ninth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the sample streams in the flow cell have a flow rate in the range of 0.001-0.01, 0.01-0.1, 0.1-1, 1-50, 50-200, or 200-1000 μl/min when the optical signal is measured from the sample streams. 
     In accordance with a thirtieth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the optical signal measured from the sample streams at the flow cell comprises scattered light, reflected light, transmitted light, fluorescence, light absorption, light extinction, or white light image, or a combination thereof. 
     In accordance with a thirty-first aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the flow sensor comprises a fluidic channel and a sensing zone on the fluidic channel, wherein the fluidic channel is fluidly connected to the flow cell to allow the sample streams to flow through; and wherein a sensing signal is measured when the sample streams enter the sensing zone. 
     In accordance with a thirty-second aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic channel in the flow sensor has a channel width in the range of about 0.001-0.05 mm, 0.05-1 mm, or 1-5 mm, and a channel depth in the range of about 0.001-0.01 mm, 0.01-0.5 mm, 0.5-1 mm, or 1-2 mm; and wherein the sample streams in the flow cell and the flow sensor have the same flow rate. 
     In accordance with a thirty-third aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the sensing zone comprises an optically transparent area configured for measuring an optical signal that changes levels between the absence and presence of the sample streams in the sensing zone. 
     In accordance with a thirty-fourth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, mixing is performed in at least one basic fluidic unit that comprises: a chamber configured to accommodate a fluid, wherein the chamber has a volume in the range of about 0.01-0.1 ml, 0.1¬0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml; a venting port connected to the chamber, wherein the venting port is connected to a pneumatic pressure source, an ambient pressure, or the atmosphere pressure; a microfluidic channel connected to the chamber, wherein the microfluidic channel has a cross section of a size in the range of about 0.001-0.01 mm2, 0.01-0.1 mm2, 0.1-0.25 mm2, 0.25-0.5 mm2, 0.5-1 mm2, 1-2 mm2, or 2-10 mm2; and a valve on the microfluidic channel. 
     In accordance with a thirty-fifth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the sample mixtures are transferred from the chamber into the flow cell to form the sample streams when an external actuation mechanism is applied to the cartridge device, and wherein the external actuation mechanism comprises a pneumatic pressure source. 
     In accordance with a thirty-sixth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, when the cartridge device is in use, the chamber is so positioned that the at least a portion of the fluid inside the chamber is pulled by gravity towards the microfluidic channel and/or away from the venting port. 
     In accordance with a thirty-seventh aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, when the cartridge device is in use, the chamber has a volume larger than the volume of the fluid accommodated therein and an air gap exists between the venting port and the fluid accommodated therein. 
     In accordance with a thirty-eighth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, at least two separate sample mixtures are transferred into the same flow cell to form at least two separate sample streams. 
     In accordance with a thirty-ninth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, a method for analyzing particles in a sample includes applying the sample to a cartridge device, which is configured for collecting a predetermined sample volume into the cartridge device; transferring the cartridge device into a reader instrument device; mixing at least a portion of the collected sample and at least a portion of a reagent to form one or more sample mixtures inside the cartridge device; forming one or more sample streams from the one or more sample mixtures in a flow cell inside the cartridge device, wherein at least two separate sample mixtures are transferred into the same flow cell to form at least two separate sample streams without a sheath flow; measuring an optical signal from the sample streams at the flow cell to detect the target particles in the sample streams; and using the reader instrument device to analyze the measured optical signal to quantify the target particles in the sample. 
     In accordance with a fortieth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, a portion of the collected sample is mixed with a first reagent to form a first sample mixture and another portion of the collected sample is mixed with a second reagent to form a second sample mixture; and wherein the two sample mixtures are separately transferred into the flow cell to form two separate sample streams. 
     In accordance with a forty-first aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the two sample mixtures are separately formed in a chamber or separately transferred into a chamber before being separately transferred into the flow cell. 
     In accordance with a forty-second aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the chamber has a volume in the range of about 0.01-0.1 ml, 0.1-0.2 ml, 0.2-0.4 ml, 0.4-0.8 ml, 0.8-2 ml, or 2-10 ml. 
     In accordance with a forty-third aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the sample is collected into a fluidic conduit. 
     In accordance with a forty-fourth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic conduit is closed by a valve and/or sealed by an external structure after the sample is collected into the fluidic conduit. 
     In accordance with a forty-fifth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, the fluidic conduit is configured for collecting a predetermine sample volume in the range of about 0.1-1 μL, 1-5 μL, 5-10 μL, 10-20 μL, or 20-50 μL. 
     In accordance with a forty-sixth aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, at least a portion of the reagent is transferred into the fluidic conduit to flush a portion of the collected sample into a chamber to form a sample mixture. 
     In accordance with a forty-seventh aspect of the present disclosure, which may be used in combination with any other aspect or combination of aspects listed herein, at least one sample stream comprises white blood cells as the target particles detected in the flow cell and at least another sample stream comprises red blood cells and/or platelet cells as the target particles detected in the flow cell.