FIELD OF THE INVENTION

This invention relates to an apparatus and method for the classification of white blood cells using two large angle light scattering channels.

BACKGROUND OF THE INVENTION

Optical flow cytometry is an established means of counting and classifying particles contained within a fluidic sample (Shapiro, H. M., Practical flow cytometry, Third Edition, Wiley-Liss publishers, New York, 1995). One application involves theanalysis of a blood sample for the purposes of determining the numbers of platelets, red blood cells (RBCs), and white blood cells (WBCs) per unit volume. This is a common clinical measurement, and optical cytometers have been incorporated into a numberof commercial hematology analyzers. Recently, microfluidic techniques have been employed for the purposes of developing cytometers which require smaller sample and reagent volumes (Altendorf, E. et al., "Differential blood cell counts obtained using amicrochannel based flow cytometer," Sensors and Actuators [1997] 1:531-534; Sobek, D. et al., "Microfabricated fused silica flow chambers for flow cytometry," Solid-State Sensor and Actuator Workshop, Hilton Head Island, S.C. [1994]; Miyake, R. et al.,"A development of micro sheath flow chamber," Proceedings of the IEEE micro electro mechanical systems workshop, Nara, Japan [1991] 265-270). Analytical instruments based on these efforts will be smaller and more portable than conventional devices.

Knowledge of the number and nature of blood cells is important for disease diagnosis. For this reason, complete blood counts and white cell differentials are common clinical diagnostic tests carried out using a hematology analyzer. Forwardangle light scattering (FALS) is sensitive to particle size and can be used to distinguish platelets from red blood cells. Small angle scattering (SALS) or large angle light scattering (LALS) in combination with FALS can distinguish within the WBCsbetween granulocytes, lymphocytes and monocytes (Salzman, G. C. et al. (1975), "Cell Classification by Laser Light Scattering: Identification and Separation of Unstained Leukocytes," Acta Cytologica 19:374-377). However, within the granulocytes, SALSand FALS cannot clearly distinguish between eosinophils and the remaining granulocytes such as neutrophils and basophils.

The difference in intensity of scattered light between s-polarized and p-polarized light can be used to further distinguish between the granulocytes. At small angles scattering of the two polarizations is indistinguishable. At large angles, WBCsized structures with no internal structure show only a small difference between the scattered light intensity of the two polarizations. Granulocyte WBCs, having an internal structure comprising numerous small granules, exhibit a difference inscattering intensity between the polarizations. In eosinophils the granules are birefringent and act to depolarize the scattered light, thereby reducing the difference in scattering intensity between the two polarizations. This depolarization has beenused to distinguish cell types (Terstappen, L.W.M.M. et al. (1988), "Four-Parameter White Blood Cell Differential Counting Based on Light Scattering Measurements," Cytometry 9:39-43; de Grooth et al., U.S. Pat. No. 5,017,497; Marshall, U.S. Pat. No.5,510,267. The depolarization was measured by impinging polarized light on a sample, collecting the large angle scattered light at a single large angle, splitting the collected light into two beams and measuring the scattered light in the two beamsusing two detectors, one for orthogonal light scattering of all polarizations, and the second preceded by a polarizing filter to measure depolarized orthogonal light scattering.

SUMMARY OF THE INVENTION

This invention provides an analyzer and a method for distinguishing polarization-preserving particles from depolarizing particles without requiring polarizing filters. This analyzer is especially useful with planar flow cells but can also beused with conventional round flow cytometers. The analyzer comprises a polarized light source positioned to produce a light beam which intersects a liquid sample flow in a flow cell. Light scattered by particles in the sample is measured by a first anda second large angle light scattering channel, positioned to receive scattered light at large angles .theta..sub.1 and .theta..sub.2, respectively. Each LALS channel comprises a photodetector and collection optics. No polarizing or wavelength filtersare required as part of the LALS detection channels. The scattered intensity at each channel is obtained and the relative intensities are used to classify the particles. While this invention can be used with any type of flowing particle, it isparticularly suited to a hematology analyzer used to count and classify blood cells, and in particular eosinophils. Preferably .theta..sub.1, is between about 15.degree. and about 50.degree., more preferably about 30.degree..+-.10.degree., and mostpreferably about 39.degree..+-.10.degree. where the flow cell is positioned at an oblique angle to the light beam. Preferably, .theta..sub.2 is between about 50.degree. and about 130.degree., more preferably about 90.degree..+-.15.degree., or about115.degree..+-.10.degree., and most preferably about 73.degree..+-.10.degree. where the flow cell is positioned at an oblique angle to the light beam.

The flow cell is preferably planar and positioned at Brewster's angle to the light beam, which for glass and plastic windows in the flow cell is about 56.degree.. The analyzer can further include small angle and forward angle light scatteringchannels, which can be used to distinguish between particles based on size and shape. The forward angle light scattering (FALS) detector is preferably placed at an angle .theta..sub.F of between about 0.5 and about 3.degree., although it can be placedat a 0.degree. angle for absorption measurements. When the FALS detector is used for absorbance measurements with a laser light source, filters will be required as is known to the art because of the intensity of the light beam. The small angle lightscattering detector (SALS) is preferably placed at an angle .theta..sub.S greater than .theta..sub.F, of between about 2.degree. and about 10.degree.. The analyzer can further include an absorption channel for measuring particles containing absorptivespecies such as dyes, hemoglobin and bilirubin. The absorption measurement can be carried out in the same stream as the scattering measurement, in the same or a different measurement zone, or in a separate stream. The absorption channel comprises alight source positioned to illuminate a sample flow, collection optics positioned to collect the transmitted light, and a photodetector. The collection optics can include a wavelength filter. The analyzer can further include additional detectors suchas a second absorption channel comprising collection optics with a second wavelength filter and a photodetector. The analyzer can further include a fluorescence channel, comprising a fluorescence photodetector and fluorescence collection optics. Thefluorescence channel can utilize the scattering light source or a separate light source.

This invention also provides a method for distinguishing polarization preserving particles from depolarizing particles, comprising the steps of: flowing said particles through a p-polarized light beam; measuring the scattered light intensityI(.theta..sub.1) at a first large angle, .theta..sub.1 ; measuring the scattered light intensity I(.theta..sub.2) at a second large angle, .theta..sub.2, wherein .theta..sub.2 >.theta..sub.1 ; and comparing I(.theta..sub.1) to I(.theta..sub.2),thereby distinguishing polarization preserving particles from depolarizing

particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an analyzer employing dual LALS detection.

FIG. 2 is a white blood cell model used for Mie scattering calculations.

FIG. 3 is the calculated scattering intensity as a function of scattering angle for the outer cell membrane and cytoplasm of the modeled white blood cell.

FIG. 4 is the calculated scattering intensity as a function of scattering angle for the nucleus of the modeled white blood cell.

FIG. 5 is the calculated scattering intensity as a function of scattering angle for granules in the modeled white blood cell.

FIG. 6 is the calculated scatter plot for (A) agranular leukocytes (B) granular leukocytes with polarization-preserving granules and (C) granular leukocytes with depolarizing birefringent granules

FIG. 7 is an analyzer having dual LALS, SALS, FALS and absorption detection.

FIG. 8 plots small angle light scattering pulse amplitudes for red blood cells and platelets.

FIG. 9 compares results of red blood cell and platelet measurements determined using the methods of this invention with results using a commercial hematology analyzer.

FIG. 10 is a 2-D histogram of the FALS and SALS data from a whole blood sample diluted 1:50 showing lymphocytes (L), monocytes (M) and granulocytes (G).

FIG. 11 shows an analysis of the sample of FIG. 10 using a commercial hematology analyzer.

FIG. 12 shows large angle light scattering data for 2.0 and 4.5.mu. microspheres.

DETAILED DESCRIPTION OF THE INVENTION

The analyzer with dual LALS detection with the laser beam oriented at Brewster's angle to the planar flow cell is illustrated in FIG. 1. The analyzer is used with a sample flow, in this embodiment confined in flow cell 1. The analyzer comprisespolarized light source 10 for directing polarized light beam 15, in this embodiment p-polarized, at the sample flow. The region where the light beam strikes the flow is the scattering measurement zone. The light source can be a laser, preferably aHe--Ne laser, or it can be a non-laser light source such as an arc lamp. It can be intrinsically polarized, as is a laser, or it can include an external polarizer. To minimize reflection losses at the flow cell windows, the light beam is oriented atBrewster's angle .theta..sub.b to an imaginal line normal to the flow cell. For glass or plastic windows .theta..sub.b is about 56.degree..

If a laser beam is incident on a planar flow cell such that the beam is normal to the surface of the cell, then due to internal reflections scattering angles greater than about 50.degree. and less than 140.degree. cannot be accessed. Tiltingthe flow cell relative to the incident beam allows light scattering at larger angles to be detected. If the beam is further incident at the Brewster angle .theta..sub.b and if the incident laser beam is polarized parallel to the plane containing thereflected and refracted beams (p-polarization), then losses due to reflections at the interfaces can be minimized. This angle minimizes the amount of light reflected from the flow cell window interfaces allowing more of the laser light to interact withthe sample stream. In order to make use of this optical property, the light is p-polarized as shown. This is a requirement to minimize light loss and reflection at internal and external interfaces.

Angular orientations given herein are with respect to the propagation direction of beam 15 unless otherwise stated. Note that the beam is refracted by the cell so the propagation direction within the scattering measurement zone is different fromthe direction before the flow cell. The analyzer further includes first LALS detector 20 and second LALS detector 30. This embodiment also includes SALS detector 50 and SALS mirror 55 which directs the SALS to the detector. It also includes FALSdetector 40 and beam block 45 which prevents beam 15 from striking the FALS detector. The photodetectors are preferably photodiodes. Each detector can be coupled with the scattering measurement zone using detection optics. The optics for eachdetection channel typically include one or more lenses to gather light, and a field stop to block scattered light outside of the desired collection angles. One aspect of the present invention is that by the use of two LALS detectors it is not necessaryto include polarizing or wavelength filters in the collection optics. The angles at which the LALS detectors are positioned are preferably about 28.degree. to about 50.degree. for the first LALS detector 20 and between about 65.degree. and about81.degree. for the second LALS detector 30.

The dual LALS analyzer can be used to distinguish between agranular particles, granular particles with one or more polarization-preserving granules and granular particles with one or more depolarizing granules. The term particle is used hereinfor any non-dissolved species in a liquid sample capable of reflecting light, including cells, cell fragments, fluorescent beads, bacteria and other biological particles, polymers, dust, microcrystals and others. The analyzer is particularly suited toleukocyte discrimination, wherein agranular leukocytes include lymphocytes and monocytes, polarization-preserving granular leukocytes include neutrophils and basophils, and depolarizing granular leukocytes include eosinophils. WBC light scattering wasmodeled as follows.

The blood cell was modeled as a system comprised of three parts, the outer cell membrane and contained cytoplasm, herein called the cell component, a nuclear component, and a granular component, as illustrated in FIG. 2. All three componentswere modeled as homogenous spheres so that a Mie scattering analysis could be used to model the light scattering. Independent particle scattering (i.e., no multi-particle scattering events) was assumed so that only the light scattering properties ofthree representative spheres needed to be considered. All membrane effects were ignored, so that the majority of the scattering arises from the bulk of the scattering particle.

The intercellular medium is physiological saline (0.85%) with an index of refraction given by n.sub.s =1.335, while the intracellular medium consists of cytoplasm with an index of n.sub.c =1.35, as well as nuclear and granular material. Theindices for saline and plasma were obtained from Practical Flow Cytometry, by H. M. Shapiro, 3rd edition, p. 149. The nuclear and granular material consist of proteins, and the index of refraction of these materials is modeled after the RBC proteinhemoglobin. The RBC index of refraction is n=1.389 (Thesis by P. Wing-Poon Cheung, Effects of Blood Physiological Variations on Optical Scattering and Fiber Optic Oximetry, University of Washington, 1973) at a wavelength of 660 nm. The nuclear andgranular refractive indices are therefore n.sub.n, n.sub.g =1.389. FIG. 2 illustrates the model as well as the particle dimensions used. The wavelength of the incident light is taken to be .lambda.=685 nm.

In the model, birefringence-induced scattering was assumed to occur only for eosinophils, and to cause depolarization of the incident p-polarized light into equal components of s- and p-polarized light. Mie scattering calculations were then usedto determine the angular distributions of the scattering of these components. The degree of birefringence assumed here for the WBCs is not meant to be exact, and was chosen to demonstrate the underlying principle of the dual LALS approach.

Results from the dual LALS model are shown in FIGS. 3, 4, and 5, which display the calculated Mie scattering for each of the three cellular components. These figures indicate that most of the large angle scattering, and sensitivity topolarization at large angles, is due to the granules. Therefore, for the purposes of this model, only the granule properties were used to represent WBC scattering at large angles. Table 1 displays the LALS intensities at both large anglescharacteristic of a constructed optical configuration, for s-polarized, p-polarized, and depolarized (equal, s-polarized, and p-polarized) light. Eosinophils, with their birefringent granules, are assumed to behave as if the light were depolarizedlight. This assumes that the birefringence and scattering mechanisms can be decoupled, i.e., that the birefringence generates new incident light which is then scattered. Non-granulocytes (i.e., lymphocytes and monocytes) have smaller scatteringintensities than those in Table 1 due to the absence of granules in these cells.

TABLE 1 ______________________________________ MIE scattering results for granules p-polarized s-polarized depolarized LALS scattering detection channel intensity intensity ______________________________________ .theta..sub.1 =39.degree. 0.112 0.184 0.148 .theta..sub.2 = 73.degree. 0.0118 0.135 0.073 ______________________________________

A calculated scatter plot suggested by Table 1 is shown in FIG. 6, demonstrating how the eosinophils can be distinguished from the remaining white blood cells. The scatter in the plot is caused by the inhomogeneity in the number and size ofgranules in the cells. The shapes of the scatter plots are merely indications of possible shapes. In the method of distinguishing particles of this invention, the two LALS intensities are compared and the particles are assigned to types on the basis ofcalculated or measured data as in FIG. 6. As suggested by the figure, the ratio of the two intensities is a characteristic which can be used in assigning particles.

The calculation results shown in FIGS. 3-5 can be used to select angles for the LALS detectors. As shown in FIG. 5, the scattering from granules becomes polarization-sensitive above about 15.degree., and the maximum difference occurs at90.degree.. Comparing FIG. 5 to FIGS. 3 and 4 shows that above about 15.degree. granular scattering is predominant over cell and nuclear scattering. To identify granules a scattering angle above about 15.degree. is chosen. To further distinguishdepolarizing granules scattering is also measured at a second angle at which there is a marked difference in the scattering of s-polarized and p-polarized light. In a constructed embodiment, LALS detectors were positioned at .theta..sub.1 =39.degree. and .theta..sub.2 =73.degree..

The term large angle light scattering is used herein for scattering at angles at which granule scattering dominates, generally greater than about 15.degree.. In this analyzer the two LALS detectors are at different large angles. As suggested byFIG. 5, the first is positioned between about 15.degree. and 50.degree., and the second is positioned between about 50.degree. and 130.degree.. For optimum distinction of depolarizing particles, the detectors are at about 30.degree..+-.10.degree. and90.degree..+-.15.degree.. Preferably the LALS detectors are positioned at oblique angles to the light beam. A second consideration in detector placement is the ease of construction. In the embodiment of FIG. 1 having an angled flow cell, the LALSdetectors can most conveniently accommodate light scattering at angles of .theta..sub.1 =39.degree..+-.10.degree. and .theta..sub.2 =73.degree..+-.10.degree..

In addition to the dual LALS detectors, the analyzer can include a SALS detector and a FALS detector. The term FALS as used herein refers to light scattered at angles which can be used primarily to count particles. The lower limit on the FALSangle is determined by the incident beam shape and size. The FALS detector is preceded by a beam stop, such as an obscuration bar, to prevent the incident beam from directly striking the detector. The FALS angle is an angle allowing measurement ofabsorption and particle size and is preferably between about 0.degree. and about 3.degree., more preferably between about 0.50 and about 3.degree.. The term SALS is used herein for angles which, in combination with the FALS signal, can be usedprimarily to distinguish granular from agranular particles. The SALS angle is an angle providing information about internal structure of particles as shown by their light scattering properties, is greater than the FALS angle, and is preferably betweenabout 2.degree. and about 10.degree..

The dual LALS analyzer can also include fluorescence measuring for use when the sample has been labeled with a fluorescent dye or if it includes fluorescent beads or other fluorescent particles. For fluorescence excitation the analyzer canutilize the light scattering light source or can alternatively include a separate light source. Preferred light sources for fluorescence excitation are lasers, in particular argon ion lasers. The fluorescence excitation can take place in the scatteringmeasurement zone or at a different region of the sample flow. The fluorescence measurement can use the same sample flow as the scattering measurements or a separate flow. The fluorescence is detected at a large angle to avoid scattered light,preferably greater than about 30.degree.. A wavelength filter in front of the detector can be used to further separate fluorescent from scattered light. The fluorescence photodetector can share collection optics with one of the LALS detectors and,following a collection lens, the light can be separated with a wavelength sensitive beam splitter.

The analyzer can also include absorbance measuring for use with absorbing particles such as cells labeled with a stain, or having hemoglobin or bilirubin. As with the fluorescence measurements, the absorbance measurement can use the same or adifferent light source than the scattering measurement, positioned on the same or different flow region. Preferred light sources include LEDs. The absorbance is measured with a detector positioned on the opposite side of the sample flow from the lightsource. As a practical construction consideration, the absorption measurement is preferably performed on a separate flow region with a separate detection channel and light source from the scattering so that both FALS and SALS detectors can beaccommodated as well as the absorption detector. The detector can be preceded by a wavelength filter to select the absorption band. More than one detector, each having different wavelength filters can be employed.

FIG. 7 shows a schematic of an embodiment of the analyzer having two large angle light scattering detectors, a forward angle light scattering detector, a small angle light scattering detector, and an absorption measurement means. Laser 10 isused for the light source for the scattering measurements. The light beam 15 is focused using first focusing lens 11 and second focusing lens 13, and is directed to the sample flow in cell 1 by mirror 14. The light beam is partially reflected by amember comprising a material which is both reflective and transparent, such as cover slip 16 and photodiode 19, for monitoring of the laser power. Photodiode 19 is preceded by photodiode lens 17 and photodiode field stop 18. The laser beam interceptsthe sample flow in cell 1 to define a light scattering measurement zone. The scattered light is collected at two large angles. At a first large angle the light is collected by first LALS lens 22 and detected by first LALS detector 20, which is precededby first LALS field stop 21. At a second large angle the light is collected by second LALS lens 32 and detected by second LALS detector 30, which is preceded by second LALS field stop 31. Small angle scattering is collected by SALS/FALS lens 53 incombination with SALS lens 52 and detected by SALS detector 50, which is preceded by SALS field stop 51. It is directed to the SALS detector 50 by mirror 55. Forward angle scattering is collected by SALS/FALS lens 53 in combination with FALS lens 42and detected by FALS detector 40, which is preceded by FALS field stop 41. Mirror 55 has a hole in the center to permit transmission of the forward angle scattered light. Beam block (obscuration bar) 45 prevents the laser beam from striking FALSdetector 40 directly. Sample absorption is measured in a different portion of the sample flow from the light scattering measurement zone. Light from

LED 60, focused by LED lens 62 in combination with LED field stop 61, intercepts flow cell 1 to define an absorption measurement zone. Beam-splitting mirror 74 transmits some of the light to first absorbance detector 70 and reflects theremainder to second absorbance detector 80. First absorbance detector 70 is used in combination with filter 73, which selects a first wavelength of light, and absorbance lens 72 and absorbance field stop 71. Second absorbance detector 80 is used incombination with filter 83, which selects a second wavelength of light, LED lens 82 and LED field stop 81.

FIG. 13 shows a further embodiment of this invention which has been developed for cytometry and hematology applications. In this embodiment cylindrical lenses and prisms are used to shape and focus the incident beam into an elliptical profile. This beam is directed through the flow cell at Brewster's angle .theta..sub.b by means of two mirrors. Laser 10 directs light beam 15 through a first pair of anamorphic prisms 88 through first focusing lens 11 and a second pair of anamorphic prisms 84. The prisms broaden the beam in one direction and narrow it in another to form the elliptical profile. The elliptical beam strikes mirror 14, which directs light beam 15 through second focusing lens 13 to second mirror 86 which directs it to flow cell 1. FALS detector 40 preceded by FALS lens 42 measures light reaching it through a hole in SALS mirror 55 preceded by SALS/FALS lens 53. Light reflected from SALS mirror 55 is measured by SALS detector 50 preceded by SALS lens 52. First LALS detector 20preceded by first SALS lens 22 measures large angle scattered light. The second large angle detector 30 and second LALS lens 32 which precedes it have been moved from their positions shown in FIG. 7 to the other side of flow cell 1 to avoid backgroundstray light reflected by the FALS field stop. The FALS and SALS detectors are photodiodes and the LALS detectors are miniature photomultiplier tubes. The actual scattering angles collected by this system are: FALS detector--1.43-2.15.degree.; SALSdetector--2.15-8.44.degree.; first LALS detector--28.2-49.2.degree.; second LALS detector--107-127.degree..

EXAMPLE

Microfluidic laminate-based structures incorporating hydrodynamic focusing and flow channels with dimensions much less than 1 mm were fabricated and used to transport and analyze blood samples. Optically transparent windows integral to the flowchannels were used to intercept the sample streams with a tightly focused diode laser probe beam. The size and structure of the blood cells passing through the laser beam determined the intensity and directional distribution of the scattered lightgenerated. Forward and small angle light scattering channels were used to count and differentiate platelets, red blood cells, and various populations of white blood cells. All the blood samples used were characterized using a commercial hematologyanalyzer for comparison and validation purposes.

In order to count and classify blood cells in the manner described above, the cells must be made to pass one at a time through the incident laser beam. Traditionally this is done by using hydrodynamic focusing where the blood cell sample streamis encircled and combined in appropriate proportions with a sheath fluid stream, and both fluids are made to pass through a tapered orifice or flow channel. The hydrodynamic forces of the flowing and constricting sheath fluid then cause the samplestream to form a narrow thread of flowing cells.

Microfluidic structures can be used to spatially confine blood cells in very narrow and precisely formed channels without the need for a sheath fluid. Such microstructures cannot, however, typically accommodate high flow rates due to the shearstresses generated. The microcytometer used in this invention confines both the sample and sheath streams within a microchannel of appropriate dimensions for the assays intended.

All the experiments were performed in laminate-based planar microstructures manufactured by Micronics, Inc., Redmond Wash., as described in U.S. patent applications Ser. No. 08/823,747 filed Mar. 26, 1997, and 09/080,691 filed May 18, 1998,incorporated herein by reference to the extent not inconsistent herewith. One such device was comprised of two thin glass windows separated by a 100.mu. thick adhesive layer into which flow channels were cut. This device produced a focusing of thesample stream in one plane only, and hence is referred to herein as the 2-D flow cell. The cross-sectional dimensions of the channel containing the focused cell stream was 100.mu. by 1 mm. A second structure was formed from Mylar and Mylar-laminatesheets (3M, Austin, Tex.). The channels were cut with a CO.sub.2 laser system (ULS-25E, Universal Laser Systems, Scottsdale Ariz.). This device produced a focusing of the sample stream by fully encircling the sample stream with a sheath fluid stream,and is referred to herein as the 3-D flow cell. The cross-sectional dimensions of the channel containing the focused cell stream in this device were 100.mu. by 500.mu.. A custom control station consisting of two computer-controlled syringe pumps(Kloehn Company, Ltd. , Las Vegas Nev.) was used to provide constant sheath and sample flow rates in the micro-structures. The sample flow rate was 95 nl/s in the 2-D flow cells and 400 nl/s in the 3-D flow cells. A 9 mw, 685 nm wavelength diode lasermodule (Melles Griot, Boulder Colo.), which produced a near circular collimated 4 mm diameter beam, was used as the light source. The laser beam passed through two crossed cylindrical lenses in order to produce a focused elliptical beam with dimensionsperpendicular to the direction of propagation of 13.mu. by 105.mu. at the sample stream. Two high speed narrow format scanning photodiode detectors (Centro Vision, Newbury Park Calif.) were used to collect the FALS (1.4.degree. to 2.2.degree.) andSALS (2.2.degree. to 8.4.degree.) signals. An obscuration bar was used to block the direct laser beam from impinging on the detectors, and three lenses and a custom mirror with a central aperture (hole) were used to direct the scattered light to thedetectors. Electronics signals were collected with an AT-MIO-16E-1 data acquisition board (National Instruments, Austin Tex.) when using the 2-D flow cell, and with a custom high speed data acquisition system when using the 3-D flow cell.

All blood samples (human) were collected with vacutainer (Becton Dickinson, Franklin Lakes N.J.) tubes containing the anticoagulant EDTA, prior to preprocessing and dilution. For the RBC and platelet assays, dilution of the samples withphosphate buffered saline was carried out by external manual mixing prior to introduction to the flow system. For the white blood cell assays, external mixing of the blood sample with a commercial soft lysing reagent (Streck-Sheath, Streck Laboratories,Omaha Nebr.) was carried out prior to introduction to the instrument. Times between mixing and analysis in both cases were kept to a minimum to avoid excess lysing of white cells or osmotic distortion of the RBCs and platelets. Aliquots of all theoriginal samples, as well as aliquots of the mixed and diluted samples where possible, were analyzed with a commercial hematology analyzer (Cell-Dyn 3500R, Abbott Laboratories, Ill.) for comparison and control purposes.

FIG. 8 displays results obtained using a 1:400 prediluted sample of whole blood and a 2-D flow cell. A histogram of the SALS light scattering pulse amplitudes is shown indicating a biomodal distribution corresponding to platelets and RBCs. Integration of the area under each of the peaks was used to determine the relative percentages of RBCs and platelets in the sample. These results along with data obtained from three additional samples are plotted in FIG. 9 against RBC and plateletpercentages obtained using the Cell-Dyn 3500R. FIG. 9 indicates a good correlation between the two methods.

FIG. 10 displays results obtained using a whole blood sample diluted 1:50 in the commercial soft lyse reagent, and a 3-D flow cell in the form of a 2-D histogram of the FALS and SALS data. An analysis of an aliquot of the same sample by theCell-Dyn 3500R is shown in FIG. 11. The three dominant clusters in each plot correspond to lymphocytes (L), monocytes (M), and granulocytes (G). The microcytometer, and commercial analyzer produce similar degrees of cluster resolution. The relativecell counts (to the total white cell count) obtained with the microcytometer are 27.0% (L), 9.31% (M), and 63.7% (G), which are also in good agreement with the Cell-Dyn percentages of 26.9% (L), 9.68% (M), and 63.4% (G).

FIG. 12 shows large angle light scattering data for a flow sample containing 2.0 and 4.5.mu. microspheres used for calibrating and testing instrument performance.

The microcytometer and method described herein has demonstrated the ability of counting and classifying platelets, RBCs, various white cell populations and other particles by means of laminar flow-based microfluidic flow channels and lightscattering optics.

This invention has been described and illustrated with respect to specific components; however, as will be appreciated by one skilled in the art, other equivalent components may be substituted for those described herein. For example, the LALSand other detectors may be used to detect absorbance, fluorescence, or other signals as well as scattered light from a laser source, and multiple (more than two) LALS detectors may be used. Additional SALS and FALS detectors may also be used to collectadditional information.

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