Abstract:
There is provided a flow cell assembly in which a shuttle supports and positions a capillary with its end extending beyond the shuttle. The flow cell assembly facilitates the replacement of a flow cell which is damaged or with flow cells having capillaries of different size or shape.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims priority to provisional application serial No. 60/291,541 filed May 16, 2001. 
     
    
     
       BRIEF DESCRIPTION OF THE INVENTION  
         [0002]    This invention relates generally to flow cells for cytometers and particularly to flow cell assemblies with suspended capillaries and more particularly to flow cells which are easily replaceable or interchangeable.  
         BACKGROUND OF THE INVENTION  
         [0003]    The detection and analysis of individual particles or cells in a suspension is important in medical and biological research. It is particularly important to be able to measure characteristics of particles such as concentration, number, viability identification and size. Individual particles or cells include, for example, bacteria, viruses, DNA fragments, cells, molecules and constituents of whole blood.  
           [0004]    Typically, such characteristics of particles are measured using flow cytometers. In flow cytometers, particles which are either intrinsically fluorescent or are tagged and labeled with a fluorescent marker are caused to flow past a beam of radiant energy which excites the particles or labels or cells to cause emission of fluorescent light.  
           [0005]    Conventional flow cytometry utilizes a flow cell that must be connected to a pressurized sample in order to force the sample into a flow cell cavity or lumen. The sample is then conducted by this pressure through the cavity or lumen, and then out the other end of the capillary into a sheath flow stream of buffer that is itself pressurized. This design requires complex flow cells that are expensive and require experts to install.  
         SUMMARY OF THE INVENTION  
         [0006]    In the present invention, the sample is drawn through a suspended capillary. One or more photodetectors detect the fluorescent light emitted by the particles or labels responsive to an excitation beam of radiant energy at selected wavelengths as they move past the beam. The photodetectors respond to photons emitted by intrinsically fluorescent, tagged or labeled particles which flow through the beam to generate representative signals. A photodetector is also employed to measure light scattered by the particles to generate signals indicative of the passage and size of all particles which flow through the flow cell.  
           [0007]    Such a cytometer is described in pending U.S. patent application Ser. No. 09/844,080 filed Apr. 26, 2001, which is incorporated herein by reference. The cytometer allows rapid analysis of single cells or particles by drawing the sample through a capillary tube for in-capillary optical detection. The sample is introduced to one end of the capillary by dipping the capillary into the sample while a source of vacuum is applied to the other end of the capillary. The sample is drawn through the capillary. This simple design lends itself to use of an easily exchangeable flow cell assembly which includes a capillary tube.  
           [0008]    There is provided a flow cell assembly with suspended capillary which is replaceably mounted in the cytometer. The flow cell assembly facilitates the replacement of a flow cell with damaged or otherwise broken capillary with a cell with an undamaged capillary or with a flow cell having a different size or shape capillary.  
           [0009]    The suspended capillary format of the cytometer allows sample aspiration by simply dipping the end of the capillary into the liquid sample. By providing a convenient means of replacing or exchanging flow cells, flow cells with damaged capillaries no longer require expert knowledge to repair. The use of simple twist-to-disconnect fluidic interconnects allows the flow cell to be easily freed from the rest of the fluidic system. By providing a simple locking device to constrain the flow cell, an untrained user can easily pull the flow cell free of the flow cytometer and replace it with another flow cell with an undamaged capillary with the capillary in the same optical position or to replace the flow cell with a capillary of different shape or size. By providing a precise positioning system, the replacement flow cell capillary can be located with such accuracy as to not affect the system&#39;s performance.  
           [0010]    The flow cell/capillary replacement system allows users to quickly and affordably exchange a flow cell having a capillary of one size for a flow cell with a capillary of another size. This allows a user studying particles of one particular size to quickly reconfigure the cytometer for particles of a very different size. A flow cell with a capillary of one length may also be exchanged for a flow cell with a capillary of a different length. This allows the cytometer to be reconfigured for a wide variety of sample vial sizes. This also allows the introduction of flow cells having capillary passages long enough to reach samples contained in a well plate autoloader “docking station” below the cytometer. Users can exchange a flow cell having a capillary of one shape for a flow cell with a capillary of another shape. This allows, for example, a flow cell of a square cross-section to be replaced with flow cells of circular, rectangular, asymmetric or other cross-sections. Furthermore, this allows for forward compatibility with future innovations in the production of the flow cell tubing.  
           [0011]    The simple flow cell/capillary replacement system allows cytometer users to quickly and affordably exchange a flow cell with certain properties for a flow cell with other properties. For example, future assays developed for use in flow cytometers may require capillaries with unusual properties such as resistance to certain corrosives or coatings to reflect, block or transmit light of various wavelengths. Also, future upgrades to the basic flow cell design such as masking to block light from reflecting and refracting off the capillary walls could be accomplished easily as such improvements become available. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The invention will be more clearly understood from the following description when read in conjunction with the accompanying drawings in which:  
         [0013]    [0013]FIG. 1 is a schematic diagram of a flow cytometer employing a flow-through capillary tube.  
         [0014]    [0014]FIG. 2 is an elevational view of the flow cell assembly mounting block of the cytometer.  
         [0015]    [0015]FIG. 3 is a perspective view of the exchangeable flow cell and mounting block.  
         [0016]    [0016]FIG. 4 is a perspective view of the exchangeable flow cell and mounting block viewed at 180° from that of FIG. 2.  
         [0017]    [0017]FIG. 5 is an enlarged sectional view of the mounting block with the flow cell mounted in the block taken generally along the line  5 - 5  of FIG. 4.  
         [0018]    [0018]FIG. 6 is a perspective view of an exchangeable flow cell assembly.  
         [0019]    [0019]FIG. 7 is a cross-sectional view of the exchangeable flow cell assembly of FIG. 6.  
         [0020]    [0020]FIG. 8 is a perspective view of a rectangular capillary provided with masks for scatter detection.  
         [0021]    [0021]FIG. 9 is a sectional view of a rectangular capillary with masks for fluorescence detection. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Referring to FIG. 1, there is schematically illustrated a cytometer or particle analyzer  10  of the type disclosed in co-pending U.S. patent application Ser. No. 09/844,080 filed Apr. 26, 2001, incorporated herein by reference. As used herein, “particle” means particles or cells, for example, bacteria, viruses, DNA fragments, blood cells, molecules and constituents of whole blood. A fluid stream  11  with particles  12  flows in the direction indicated by the arrow  13 . The sample or fluid stream is drawn through a capillary or tube  15  by a suitable pump. The capillary tube can take many shapes. It can be round, square, oblong, etc. A light source, such as laser  14 , emits a light beam  16  of selected wavelength. The beam strikes particles which flow along the capillary. In order to count all particles which pass through the beam, light scattered by the particles is detected by an optical system including a detector  17 , for example a photomultiplier tube. The detector provides an output signal such as that shown by the peak  18 . The size and shape of the peak is dependent upon the size of the particle. The occurrence of the peak indicates that a particle has traversed the light beam.  
         [0023]    If the particles are intrinsically fluorescent, or if the particles have been tagged or labeled with a fluorescent dye, they will emit light  21  at characteristic wavelengths as they pass through the beam  16 . The light is detected at an angle with respect to the beam  16  so that no direct light is detected. The fluorescent light is directed to a beam splitter  22  which passes light above a given wavelength and reflects light below a given wavelength. Transmitted light is detected by detector  23  while reflected light is detected by the detector  24 . For example, the beam splitter reflects light having wavelengths less than 620 nm and transmits light having a greater wavelength. Filters, not shown, may be placed in front of the detectors  23  and  24  to pass light at specific wavelengths, such as 580 nm and 675 mn, which will permit detection of particles tagged with readily available materials which emit light at predetermined wavelengths. The output of the detectors is shown as pulses  26  and  27 . It should be appreciated that the foregoing description of a cytometer is not detailed and that an actual system will include optical elements to collect and direct the light. However, the foregoing explanation suffices in that it shows how the signals which are to be processed by the inventive signal processing system are obtained.  
         [0024]    In the present invention, the capillary  15  is mounted in a flow cell assembly  31  which is received in a cytometer block  32  forming part of the cytometer instrument (not shown) which supports the light source  14 , optics and photodetectors  17 ,  23  and  24 . The block includes an opening  33  through which the excitation light beam  16  is projected. Scattered light  20  is detected by detector  17  by blocking direct light with a beam blocker  34 . If the detector  17  is placed to detect side-scattered light, a beam blocker is not required. The fluorescent light  21  travels through a window  36 . A shaft  35  is mounted on the block  32 . The flow cell assembly  31  and cytometer block  32  are shown in more detail in FIGS.  3 - 7 . The flow cell assembly  31  includes a body with a rectangular end  38  which accommodates a capillary tube union  39 . The end  38  is threaded to receive a quick disconnect high pressure fitting  41  connected to the end of tubing  42 . The other end of the tubing is connected to a syringe pump (not shown) which draws sample fluid through the capillary  15 . When the flow cell assembly  31  is mounted in the block  32  the capillary  15  must be accurately located with respect to the light beam  16 . To this end, the capillary must be accurately positioned in the flow cell body, and the flow cell and capillary must be accurately located in the cytometer block  32 .  
         [0025]    The flow cell body is machined to form an L-shaped region  43 . This, together with the rectangular end  38 , defines an overhang or stop  44  which engages a stop region  46  of the block  32 , FIGS. 3 and 4. When the flow cell assembly is inserted into the block and the stops are engaged, portion  53  of the capillary is supported adjacent the light input aperture  47  in the body  43 . Spaced reference pins  48 ,  49  and  51 ,  52  are mounted in the flow cell body and extend beyond the faces of the L-shaped cut-out. The capillary is positioned on the pins and secured to the shuttle such as by an adhesive. As a result, the portion  53  of the capillary is accurately located with respect to the flow cell body and aperture  47 . Although the preferred embodiment includes locating pins, the body can be formed with spaced locating ridges. The outer edge of the body  43  has a camber  54  which helps guide the body as the flow cell is inserted in the block  32 .  
         [0026]    The block  32  includes an L-shaped opening  55  with reference surfaces  56  and  57 . Spaced screws  57  with spring-loaded balls  58  extend through the wall of the block  32  into the L-shaped opening  55 . The balls engage the flow cell and urge it against the reference surfaces. To install a flow cell into the cytometer, the user places the end of the flow cell into the opening. As the flow cell body is moved down into the opening, the spring-loaded balls  58  urge the shuttle reference pins against the reference walls or surfaces  56  and  57 . In view of the fact that the reference pins extend beyond the surface of the shuttle, they engage the reference surfaces and the capillary portion  53  is accurately located with respect to the light beam  16 . The insertion is terminated when the stop  44  engages block stop  46 .  
         [0027]    A further improvement is to apply masks to the outer surface of the capillary. One mask includes a slit which passes a beam having a predetermined thickness. Referring to FIGS. 8 and 9, the mask  61  on the front face of the capillary includes a slit  62  which defines the thickness of the light beam from light source  63  traversing the capillary lumen. In the embodiment of FIG. 8, a mask is provided on the back face which includes spaced slits  66  and  67 . The mask portion  68  between the slits  69  intercepts direct light. Light scattered by the particle  69  travels through the spaced slits and is detected by photodetectors  71  and  72 . In the embodiment of FIG. 9, slits  73  and  74  are formed in masks  76  and  77  on opposite sides. Fluorescent emission from the particle  69  is detected by photodetectors  78  and  79 . It is apparent that the masking arrangement of FIGS. 8 and 9 can be combined and both scattered light and fluorescent light can be detected with a single capillary.  
         [0028]    Thus, there has been provided an improved exchangeable flow cell assembly which is easy to place in a cytometer with the capillary precisely located with respect to the light beam. The capillary may be masked to enhance the optics.