{15
`United States Patent
`6,159,739
`Dec. 12, 2000
`Weigl et al.
`Date of Patent:
`[45]
`
`Patent Number:
`
`[11]
`
`US006159739A
`
`[54] DEVICE AND METHODFOR3-
`DIMENSIONAL ALIGNMENTOF
`PARTICLES IN MICROFABRICATED FLOW
`CHANNELS
`
`[75]
`
`Inventors: Bernhard Weigl; Paul Yager, both of
`Seattle, Wash.; James P. Brody,
`Pasadena, Calif.
`;
`os
`,
`[73] Assignee: University of Washington,Seattle,
`Wash.
`
`OTHER PUBLICATIONS
`
`.
`.
`:
`Chmelik, Josef, “Isoelectric focusing, field—flow fraction-
`ation” Journal of Chromatography 545, No. 2 (1991).
`Eisert, W.G. et al. (1975), “Simple flow microphotometerfor
`rapid cell population analysis,” Rev. Sci. Instrum. 46(8):
`1021-1024.
`Sobek et al. (1993), “A Microfabricated Flow Chamberfor
`Optical Measurements in Fluids,” in Proc. of the IEEE
`Micro Electro Mechanical Systems Workshop, Fort Lauder-
`dale, Florida, Feb. 1993, pp. 219-224.
`
`[21] Appl. No.: 08/823,747
`
`(List continued on next page.)
`
`
`
`[22]
`Filed:
`Mar. 26, 1997
`Primary Examiner—Maureen M. Wallenhorst
`[51] WntaiGle” siasssssnssssacatsnweunacnass GOIN 35/08 or OGA HENSOREERIB, VERINEL BI:
`
`
`[52]
`436/52; 436/53; 436/165;
`436/172; 422/81; 422/82; 422/82.05; 422/82.08;
`[57]
`ABSTRACT
`356/246
`The present invention provides a sheath How module made
`
`[58] fromafirst plate ofmaterial having formed therein a laminarField of Search o........ccccce ceceeee 436/52, 53, 63,
`
`436/164, 165, 172;
`422/81, 82, 82.05, 82.08,
`fluid flow channel; at least two inlets, each inlet joining the
`82.09; 356/246
`laminar flow channel at a junction, the first inlet junction
`being wider than the second inlet junction, and an outlet
`from the flow channel. A second plate, e.g. a transparent
`cover plate, seals the module and allows for optical mea-
`surements. A first inlet allows for introduction of a first fluid
`into the flow channel. Thefirst fluid is the sheath fluid. A
`U.S. PATENT DOCUMENTS
`second inlet allows for introduction of a secondfluid into the
`3,873,204
`3/1975 Friedmanet al.
`. 356/39
`
`sheath fluid while it is lowing through the flow channel. The
`4,056,324
`11/1977 Gohde vossusn..
`356/246
`second fluid is the center fluid. Because the second inlet
`4,894,146
`.....csccssessseesesesseneeeee 209/12
`1/1990 Giddings
`
`junction is narrower than thefirst inlet junction, the center
`4,908,112
`204/299 R
`3/1990 Pace ou...
`
`fluid becomes surroundedon both sides by the sheath fluid.
`4,983,038
`venues 356/246
`1/1991 Ohkietal.
`
`
`
`5,007,732 4/1991 Obkiel al.oo...ecesesssssseseeseeees 356/73 After all fluids have been introduced and sheath flow has
`
`8/1991 Giddings...
`-. 210/695
`5,039,426
`been achieved,
`the depth of the flow channel can be
`
`1/1992 Miyakeetal.
`es decreased,
`5,079,959
`leading to vertical hydrodynamic focusing.
`
`LO/1992. Koosaben iicsscicsisinssscsssssascises: S56/243
`5,159,403
`Optionally, the width of the flow channel can be decreased,
`leading to horizontal hydrodynamic focusing. The decrease
`in depth and width can be gradual or abrupt. The device of
`the present invention can function in two modes, the sheath
`flow modeand the particle injector mode, depending on the
`ehlive comatice or the sheath fluid, the center fluid, and any
`particles in either fluid.
`
`_
`[56]
`
`.
`References Cited
`
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`0.288 029 A2
`4/1988
`European Pat. Off.
`.
`0 204701
`9/1992
`European Pat. Off.
`25 21 236 Al
`11/1976 Germany.
`WO 97/00442
`1/1997 WIPO .
`
`48 Claims, 12 Drawing Sheets
`
`ie 3c
`
`30
`
`3I
`
`9
`
`1 |h
`
`ci
`
`20
`
`DD
`
`5
`
`el
`
`ABSGlobal, Inc. and Genus ple — Ex. 1005, p. 1
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`

`

`6,159,739
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`8/1993 Caldwell et al... seen 210/748
`5,240,618
`
`5,674,743 10/1997 Ulmer........... . 433/287.2
`5,716,852
`2/1998 Yager etal.
`......
`vee 436/172
`
`...
`ww. 356/246
`5,726,751
`3/1998 Altendorf et al.
`
`5/1998 van den Enghet al.
`.
`ween 436/172
`5,747,349
`
`we 210/634
`.........
`$,932,100
`8/1999 Yager et al.
`
`9/1999 Weigl et al. vices 436/52
`5,948,684
`....cccccseesceseteeeeee 436/34
`5,972,710 10/1999 Weigh et ab.
`OTHER PUBLICATIONS
`
`Gravesen, P. et al. (1993), “Microfluidics —a review,” J.
`Micromech. Microeng 3:168-182.
`Kikuchi, Y. et al. (1992), “Optically Accessible Microchan-
`nels Formed in a Single—Crystal Silicon Substrate for Stud-
`ies of Blood Rheology,” Microvascular Res. 44:226-240.
`
`Miyake, R. et al. (1991), “A Development of Micro Sheath
`Flow Chamber,” in Proceedings of the IEEE Micro Electro
`Mechanical Systems Workshop, Nara, Japan, Jan. 1991, pp.
`265-270.
`
`Verpoorte, E. et al. (1993), “A silicon flow cell for optical
`detection in miniaturized total chemical analysis systems,”
`Sensors and Actuators B 6:66-70.
`
`Wilding, P. et al. (1994), “Manipulation and Flow of Bio-
`logical Fluids in Straight Channels Micromachined in Sili-
`con,” Clin. Chem. 40(1):43-47.
`
`Sobek, D. et al. (1994), “Microfabricated Fused Silica Flow
`Chambers for Flow Cytometry,” Solid State Sensor and
`Actuators Workshop, Hilton Head, South Carolina, Jun.
`1994, 4 pp.
`
`ABS Global, Inc. and Genus plc – Ex. 1005, p. 2
`ABS Global, Inc. and Genus plc — Ex. 1005, p. 2
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`U.S. Patent
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`Dec. 12, 2000
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`
`PRIOR ART
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`

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`6,159,739
`
`1
`DEVICE AND METHOD FOR3-
`DIMENSIONAL ALIGNMENTOF
`PARTICLES IN MICROFABRICATED FLOW
`CHANNELS
`
`This invention was made with government support. The
`government has certain rights therein.
`FIELD OF INVENTION
`
`This invention relates generally to an apparatus and
`methods for achieving sheath flow using a microfabricated
`flow channel. The invention is useful, for example,
`for
`injecting small particles into a sheath stream, for achieving
`sheath flow in a flow cytometer and in creating hydrody-
`namic focusing.
`BACKGROUND OFTHE INVENTION
`
`15
`
`Flow cytometry is a sensitive and versatile probe of the
`optical characteristics of microscopic particles, with wide-
`spread applications including hematology,
`immunology,
`genetics,
`food science, pharmacology, microbiology,
`parasitology, and oncology. Optical flow cytometers use
`light scattering and fluorescence to determine physical and
`chemical properties of the particles. For measurement, par-
`ticles are arranged in single file, typically by hydrodynamic
`focusing within a sheath fluid, and interrogated by a light
`beam propagating orthogonal to the flow axis. Flow cytom-
`elers often use two concentric fluids to carry particles
`through the measurement zone, where optical measurement
`occurs. The use of two concentric fluids facilitates the
`passage ofthe particles through the measurement zonein a
`single file fashion, and helps avoid clogging of the flow
`channel. Hydrodynamic focusing is a phenomenon that
`leads to a single file flow of particles as a result of the very
`small dimensions of the flow channel. A sampleis injected
`into a flowing sheath fluid;
`the dimensions of the flow
`channel become more narrow, causing the dimensionsof the
`stream of sample to become more narrow also. FIG. 1 is a
`cross section of flow in an art-known sheath flow accom-
`plished by injecting, via a needle or other concentric
`opening, a center fluid (41) containing a sample with par-
`ticles (42)
`into a sheath fluid (40), surrounded by air.
`Hydrodynamic focusing requires laminar flow of the fluids;
`any turbulence would cause mixing of the concentric fluids.
`The optical properties of the particles are measured in the
`measurement zone. Scattered light and fluorescence are
`measured by two or more photodetectors positioned around
`the illuminated portion of the flow stream. A first photode-
`tector can be positioned to collect small angle scattering. A
`second photodetector is often positioned at about 90° to the
`forward scattering direction to collect large angle scattering
`and fluorescence.
`
`Existing commercial cytometers are large and compli-
`cated instruments requiring skilled operators. ‘To increase the
`accessibility of flow cytometry, compact cytometers are
`desired.
`
`The flow behavior ofliquids at the microscopic level is
`significantly different from the flow behavior of liquids at
`the macroscopic level. In microstructures, i.e. microfabri-
`cated fluidic devices, practically all flow is laminar, as a
`result of the extremely small channel diameters. Laminar
`flow allows two or more fluids to flow parallel to each other
`without turbulence-induced mixing. However, because the
`channel diameters are very small, diffusion is significant.
`Since diffusion occurs in all directions, a component of one
`layer may diffuse to another layer, perpendicular to the
`direction of flow.
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`Sheath flow is a particular type of laminar flow in which
`one layer is surrounded by another layer on more than one
`side. Concentric layers of fluids, that is, where one layer is
`completely surrounded onall sides by another layer, is one
`example of sheath flow. Sheath flow is useful because it
`positions particles with respect to illuminating light, e.g., a
`laser beam, and it prevents particles in the center fluid,
`which is surrounded by the sheath fluid, from touching the
`sides of the flow channel and thereby prevents clogging of
`the channel. Sheath flow allowsforfaster flow velocities and
`higher through-put of sample material. Faster flow velocity
`is possible without shredding cells in the center fluid
`because the sheath fluid protects the cells from shear forces
`at the walls of the flow channel. Sheath flow is useful in
`many applications, including but not limited to, any appli-
`cation in which it is preferable to protect particles by a layer
`of fluid, for example in applications whereinit is necessary
`to protect particles from air. Other applications include flow
`cytometry and combustion processes wherein an inner core
`layer burns at a different temperature from that of an outer
`layer. In the latter application, the sheath flow module ofthis
`invention can be used to create a flame of two or more
`combustible fluids with the outer sheath fluid burning, for
`example, al a higher temperature than the inner core fluid. In
`this case, the outer sheath fluid can be used to heat the inner
`core fluid. Of course, the temperatures of the fluids can be
`reversed, i.e., the outer sheath fluid can be one which burns
`at a lower temperature than the inner core fluid. Control of
`flame shape or color
`is possible using the sheath flow
`module of this invention.
`
`In a microfabricated flow channel, a challenge is to focus
`light into the channel and to collect near forward scattered
`and high angled scattered light out of the channel. A few
`microfabricated flow cytometer flow channels have been
`reported. Miyake et al. [Proceedings of the IEEE Micro
`Electro Mechanical Systems Workshop, pp. 265-270, Nara,
`Japan, January 1991] describes a micromachined sheath
`flow channel madeoffive stackedplates. Three metal plates
`are used to create a flow having a sample core within a
`sheath, and glass plates on the top and bottom of the stack
`provide optical access to the flow channel for illumination
`through the top and forward scattered light collection
`through the bottom. The top and bottom plates provide a
`sheath fluid inlet. The middle plate provides for the sample
`inlet in the center, with the sheath fluidinlets on both sides.
`It appears that 90° scattering cannot be collected. Sobek et
`al. [Proceedings of the IEEE Micro Electro Mechanical
`Systems Workshop, pp. 219-224, Fort Lauderdale, Fla.,
`February 1993] describes a four-layer silicon microfabri-
`cated hexagonal sheath flow channel. The channel is formed
`between two of the silicon wafers.
`Integrated optical
`waveguides intersecting the channel are used to couplelaser
`light into the channel and out of the channel in the forward
`direction. At this intersection, the top and bottom walls of
`the channel are silicon nitride/silicon dioxide windowsfor
`90° light collection, Each window is fabricated by growing
`an oxide layer on a silicon wafer, bonding the oxide layerto
`a second silicon wafer, etching away the silicon on both
`sides of the oxide at the window region and depositing a
`nitride layer. Sheath flow with a sample in the center of the
`sheath stream is accomplished by injecting sample via a
`hypodermic needle into the center of the stream of sheath
`fluid. Sobek et al. [Proceedings of the Solid-State Sensors
`and Actuators Workshop, Hilton Head, 8.C., June 1994]
`describes a sheath flow channel fabricated between two
`fused silica wafers. To couple light into the channel and out
`in the forward direction, optical
`fibers are sandwiched
`
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`

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`6,159,739
`
`3
`between the wafers orthogonal to the flow axis. Fluores-
`cence is collected through the upper transparent wafer.
`Again, sheath flow is accomplished by injection of the
`sample via a hypodermic needle into the center of the sheath
`stream.
`
`U.S. Pat. No. 5,726,751, “Silicon Microchannel Optical
`Flow Cytometer,” issued Mar. 10, 1998, which is incorpo-
`rated by reference herein in its entirety, discloses a flow
`cytometer comprising a v-groove flow channel formed by
`micromachining a silicon wafer. This reference describes a
`flow cytometer made of two components: a flow cytometer
`optical head and a disposable flow module. The flow module
`of this reference exploits the fact that anisotropic etching of
`single crystalline silicon wafers provides access to reflective
`surfaces with precisely etched angles relative to the surface
`of the wafer. The facets are used for reflecting, as opposed
`to transmitting, an illuminating laser beam. This reference
`suggests the use of a sheath flow in a v-groove but does not
`teach a novel method or apparatus for achieving sheath flow.
`SUMMARY OF THE INVENTION
`
`4
`junction, into an established sheath fluid. Unlike the previ-
`ously known devices which create sheath flow (e.g. Miyake
`et al.), the present invention does not need sheath inlets on
`each side of the flow channel, Optionally, to get sheath fluid
`above and below the center fluid so that the center fluid is
`entirely surrounded by sheath fluid, a third inlet can be
`provided for introduction of sheath fluid downstream of the
`center fluid (second) inlet. The sheath flow module may be
`oriented in any way, e.g., horizontally, vertically, or tilted
`(with respect to the long axis of the flow channel).
`In this modethe inlets may be on the bottom ortop of the
`flow channel. This results in sheath fluid on twosides and
`
`15
`
`either the top or the bottom, respectively. If the module is
`oriented with the inlets on the bottom of the flow channel,
`then upon introduction of the center fluid, sheath flow is
`accomplished with the center fluid surrounded by the sheath
`fluid on the top and on the sides. Alternatively, if the module
`is oriented with the inlets on the top ofthe flow channel, then
`upon introduction ofthe center fluid, sheath How is accom-
`plished with the center fluid surrounded by the sheath fluid
`on the bottom andon thesides.
`
`30
`
`40
`
`‘To surround the center fluid on all sides, the sheath flow
`invention provides a sheath flow module
`The present
`made from a first plate, which is a single piece of material,
`module of the present
`invention may further comprise
`additional inlets, for instance, a third inlet, downstream of
`and a second plate, which is preferably a transparent cover
`plate. This module allows for sheath flow creation and
`the second inlet. The third inlet may be used to introduce any
`optical measurements of a sample ofinterest. The sheath
`desired fluid. For example, a third inlet may be included to
`flow module of the present invention can be employed to
`introduce a second layer of sheath fluid so that the center
`achieve sheath flow on a microscale for use in flow cytom-
`fluid is surrounded on all sides by the sheath fluid. If the
`etry. An object of the present invention is to provide a flow
`third inlet is used for introducing sheath fluid, the third inlet
`module for reproducibly focusing particles into the mea-
`is preferably wider than the second inlet, more preferably
`surement zone of a flow cytometer, Another object of the
`approximately the same width as thefirst inlet. Alternatively,
`invention is to prevent particles from touching the walls/
`a third or additional inlet may be included to, for example,
`sides and bottom and top of the flow channel.
`introduce a reagent which chemically reacts with or other-
`wise modifies a sample already introduced.
`The present
`invention provides a sheath flow module
`35
`The laminar flow channel of the sheath flow module ofthe
`made fromafirst plate of material having formed therein a
`laminar fluid flow channel; at
`least two inlets, each inlet
`present invention can increase in depth at any and/or each
`joining the laminar ow channel at a junction, thefirst inlet
`inlet. For example, the depth of the channel may be greater
`junction being wider than the second inlet junction, and an
`between the second inlet junction and the outlet than the
`outlet from the flow channel. A second plate, e.g. a trans-
`depth between the first and secondinlet junctions. Ifa third
`parent cover plate, seals the module and allows for optical
`inlet is present, the depth of the channel between the second
`measurements.
`and third inlet junctions may be greater than the depth
`between the first and secondinlet junctions but less than the
`depth between the third inlet junction and the outlet. An
`increase in depth provides for introduction of an additional
`fluid layer with retention ofall fluid layer dimensions (layers
`already flowing in the channel, as well as the newly injected
`layer). This retention of all
`fluid layer dimensions is
`preferable, but not necessary.
`After all fluids have been introduced and sheath flow has
`been achieved,
`the depth of the flow channel can be
`decreased,
`leading to vertical hydrodynamic focusing.
`Optionally, the width of the flow channel can be decreased,
`leading to horizontal hydrodynamic focusing. The decrease
`in depth and width can be gradual or abrupt.
`The second mode, termed the particle injector mode, is
`useful in cases in which the center fluid contains particles
`which are denser or less dense than the fluids surrounding
`them.
`In the present
`invention, one or both fluids may
`contain particles. If the particles are denser than the fluids
`surrounding them,
`the particles settle out of the fluids
`(gravity pulls the particles down), and hence the particles
`can elude measurement. In the present invention, this prob-
`lem ofparticlessettling out ofthe fluids as a result of gravity
`can be avoided by orienting the sheath flow module verti-
`cally. Alternatively, gravity can be exploited by orienting the
`module horizontally and positioning the inlets on top of the
`
`The present invention provides the creation of sheath flow
`from a single plate with formed features, covered by a
`second plate. The second plate can cither be a flat cover
`plate, preferably transparent, or it can have a channel and/or
`inlets and/or an outlet formed therein. A transparent cover
`plate allows for optical measurements by reflection, in cases
`where thefirst plate is a reflective material, e.g. silicon. In
`cases where the first and second plates are both transparent,
`optical measurements can be performed by transmission.
`There is no needto fabricate and align multiple plates or use
`a syringe needle for injection.
`A first inlet allows for introduction ofa first fluid into the
`flow channel. Thefirst fluid is the sheath fluid. Asecondinlet
`allowsfor introduction of a second fluidinto the sheath fluid
`while it is flowing through the flow channel. The second
`fluid is the center fluid. Because the secondinlet junction is
`narrower than the first
`inlet
`junction,
`the center fluid
`becomes surrounded on both sides by the sheath fluid.
`The device of the present invention can function in two
`modes, the sheath flow mode andthe particle injector mode,
`depending on the relative densities of the sheath fluid, the
`center fluid, and any particles in either fluid.
`The first mode, termed the sheath flow mode,is for fluids
`and particles of approximately equal densities, and creates
`sheath flow by introducing a center fluid, via a narrow inlet
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`6,159,739
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`5
`module. In this mode, particles are injected by first estab-
`lishing a flow ofsheath fluid whichis introduced viathe first
`inlet, and then introducing particles or particle-containing
`center fluid via the second inlet. Because the particles are
`denser than the center and sheath fluids, gravity acts to
`center the particles in the vertical dimension. Thus,
`the
`second mode ofthis invention provides for deliberate mix
`(as a result of gravity) of a center fluid constituent with
`sheath fluid (which was avoided in the first mode) and
`allows the particles to be surrounded onall sides by sheath
`fluid (which was accomplished by a third inlet in the first
`mode).
`If the particles are less dense than the surrounding fluids,
`they can be injected from the bottom, from whencethey float
`upwardas a result of their buoyancy.If the particles are less
`dense than the surrounding fluids,
`it may be preferable to
`introduce a second sheath fluid, via a third inlet, especially
`if the particles are injected from the top.
`In the second mode, the injected particles can be fluores-
`cent beads.It is preferable to have the inlets on the top ofthe
`flow channel in this mode. Thus, gravity causes the particles
`to fall slowly as the fluids flow through the channel. U.S.
`Pat. No. 5,747,349 issued Mar. 5, 1998, “Fluorescent
`Reporter Beads for Fluid Analysis,” which is incorporated
`by reference herein in its entirety, discloses reporter beads
`for chemical analysisoffluid properties such as pH, oxygen
`saturation and ion content. A fluorescent property of the
`reporter bead, such as intensity, lifetime or wavelength, is
`sensitive to a corresponding analyte. Reporter beads are
`added to a fluid sample and the analyte concentration is
`determined by measuring the fluorescence of individual
`beads. Beads tagged with different reporter molecules allow
`for a plurality of analytes in a sample to be measured
`simultaneously. Alternatively, absorptive beads tagged with
`reporter molecules which change absorbance as a function
`of analyte concentration can be employed in a manner
`similar to the fluorescent beads.
`
`For use in either mode, the module can include a mea-
`surement zone between the most downstream inlet and the
`outlet. The measurement zone provides optical access for
`measurements such as scattering, absorbance, fluorescence
`and emission. The distance between an inlet through which
`particles are introduced and the outlet is preferably chosen
`such that, for a given flow speed, the particles do not touch
`the bottom ortop of the flow channel. In the particle injector
`mode, the measurement zone is preferably positioned so that
`the particles are surrounded on all sides by fluid and have not
`dropped so close to the bottom orfloated so close to the top
`of the flow channel that optical measurements are hindered.
`In a preferred embodiment, optical measurements exploit
`reflection from the channel walls, as described in U.S. Pat.
`No. 5,726,751 “Silicon Microchannel Optical Flow
`Cytometer,” issued Mar. 10, 1998.
`Prior to the measurement zone, the diameter of the flow
`channel can taper from a wider to a narrower downstream
`portion. This narrowing of the channel leads to horizontal
`hydrodynamic focusing.
`The sheath flow module ofthis invention can be applied
`to many systems. For example, the sheath fluid may be a
`sample fluid and the particles in the center fluid may be
`reporter beads. Alternatively, the sheath fluid may be aninert
`fluid and the center fluid may be a sample, e.g., blood. These
`are just a few of the many types of systems in which the
`present invention can be applied.
`The sheath flow module may be made from any etchable,
`machinable or moldable material, e.g. silicon wafers,
`plastics, and casting materials.
`
`6
`This invention further provides methods for focusing a
`center fluid in a sheath fluid using the sheath How module of
`the present invention. The methods include introducing a
`sheath fluid into the first inlet; introducing a center fluid into
`the second inlet, and optionally introducing a third fluid
`(which may be sheath fluid) into an optional third inlet. The
`center fluid may be a sample fluid, and/or may contain
`reporter beads. The sheath fluid may be a particle-free
`carrier fluid (optically inert) or it may contain particles. The
`sheath fluid may be a sample fluid, e.g. whole blood.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a cross section of sheath flow achieved by a
`known method.
`
`FIG. 2 is a cross section of a v-groove flow channel.
`FIG. 3A is a lengthwise section through the center of the
`sheath flow module of this invention.
`
`FIG. 3B is a top view of the sheath flow module of this
`invention.
`FIG, 3C is a cross section of the flow channel of FIGS. 3A
`and 3B and sheath flow attained therein.
`
`FIG. 4A is a lengthwise section of a particle injector,
`showingfalling particles.
`FIG, 4B is a top view ofa particle injector, showing the
`relative widths of inlets and portions of the laminar flow
`channel.
`
`FIG, 3A is a lengthwise section through the center of a
`sheath flow flow cytometer.
`FIG. 5B is a top view of the sheath flow flow cytometer
`of FIG. 5A.
`
`FIG. 5C is a lengthwise section through the flow channel
`some distance from the center, i.e. not through the second
`inlet, in the flow channel of FIGS. 5A and 5B in which the
`depth of the channel increases at the secondinlet only across
`the width ofthe second inlet and increases across the entire
`width of the channelat the third inlet.
`
`FIG. 5D is a cross section of the fluid flowing in the flow
`channel of FIGS. 5A, B and C.
`FIG, 6 is a lengthwise section through the flow channel
`some distance from the center, ic. not through the second
`inlet, in an alternative embodiment to the flow channel of
`FIGS. 5A-SD.
`
`FIG, 7, comprising FIGS. 7A—7D,showscross sections of
`various embodiments of the flow channel of this invention.
`
`FIG. 8A showsthe relative velocities of the various layers
`offluids in the laminar flow channel.
`
`FIG. 8B is a velocity histogram of fluorescent beads in a
`sheath flow channel. Frequency (a measure ofthe number of
`beads) versus velocity of the beads is graphed.
`FIG. 9 illustrates the channels of an embodiment of the
`“H” filter of U.S. Pat. No. 5,932,100 issued Aug. 3, 1999.
`FIG. 10A illustrates a sheath flow module, having a
`branching flow channel.
`FIG. LOB illustrates the use of a branching flow channel
`to divide the fluid flowing through the flow channel.
`FIG. 10C shows the branching flow channels of a sheath
`flow module.
`
`FIG. 10D showsthat the branching flow channels may
`join the flow channel at angles other than 90 degrees.
`FIG. LLA showsthe sheath flow module creating a flame.
`FIG. 11B showsthe sheath flow module with an outlet at
`the downstream end ofthe channel for introducing particles
`into a flame for emission spectroscopy.
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`7
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The sheath flow module of the present invention provides
`that a center stream is surrounded on more than one side and
`optionally on all sides by a sheath fluid. This provides a way
`to position a particle in the channel. This helps prevent
`clogging ofthe flow channel and provides a uniform speed
`of
`the particle in the channel. Precise positioning and
`uniform speed ofparticles are generally useful in detection
`schemes, ¢.g., in flow cytometry.
`The term sheath fluid refers to a layer of fluid, which may
`contain particles, surrounding on more than oneside a center
`fluid. The term center fluid refers to a layer of fluid, which
`may contain particles, whichis surrounded on more than one
`side by a sheath fluid.
`The sheath fluid can be an optically and chemically inert
`fluid or it can be a sample containing cells and/or analytes
`of interest.
`
`The center fluid can be a sample fluid which can contain
`fluorescent reporter beads, and/or cells and/or analytes of
`interest and/or a chemical indicator and/or a reagent which
`reacts with an analyte of interest to give a change in detected
`optical properties. The center fluid can be a non-sample fluid
`which contains reporter beads, an indicator or a reagent.
`The term particles has the common meaning,and refers to
`undissolved solid matter, and specifically includes cells and
`fluorescent beads.
`
`FIG, 2 is a cross section of a v-groove flow channel. A
`v-groove (56) is etched in a silicon wafer (43) and the
`channel is sealed by a transparent, e.g. glass, cover plate
`(44). A particle (42) is surrounded by sample fluid (41).
`The sheath flow module of this invention is illustrated in
`FIGS. 3A, 3B and 3C. FIG. 3A is a lengthwise section
`through the center of the flow module. Plate (1) is machined,
`molded or etched to form the flow channel. The plate can be
`selected from the following which include, but are not
`limited to, silicon wafers, plastics, e.g. polypropylene, and
`casting materials. Techniques for etching silicon wafers and
`molding and machining plastics are well-known in the art.
`The plate has at least one surface (6), which is a substan-
`tially flat plane. A laminar flow channel (8)is formed in flat
`plane of the plate. The term laminar flow channel is used
`herein to refer to a flow channel having dimensions that
`allow for laminar flow. Surface (6) is termed herein the
`channel surface. The laminar flow channel has an upstream
`end (7) and a downstream end (9). A first inlet (10) passes
`through the plate at the upstream end of the channel and
`joins the flow channel at first inlet junction (11). An outlet
`(30) passes through the plate at the downstream end of the
`channel and joins the flow channelat outlet junction (31). A
`second inlet (20) passes through the plate between the first
`inlet andthe outlet and joins the low channel at second inlet
`junction (21), which is narrower thanthe first inlet junction.
`Asecondplate (5) is sealed to the flat plane of the first plate,
`thereby forming one side of the laminar flow channel.
`A view ofthe channel surface is illustrated in FIG. 3B.
`
`The relative widths of the inlet junctions are shown, as well
`as the edge (12) of the flow channel (8). The second inlet
`junction (21) is narrower than thefirst inlet junction (11).
`Referring again to FIGS. 3A and 3B, a sheath fluid is
`introduced into the flow channel (8) via the first inlet (10)
`and flows through the flow channel toward the outlet (30).
`The sheath fluid can be an inert carrier fluid or it can be a
`sample fluid containing cells, e.g. whole blood, or other
`analytes. The term carrier fluid is used herein