‘AON
`
`1040043506
`
`as) United States
`a2) Patent Application Publication (0) Pub. No.: US 2004/0043506 Al
`(43) Pub. Date: Mar. 4, 2004
`
`Haussecker etal.
`
`(54) CASCADED HYDRODYNAMIC FOCUSING
`IN MICROFLUIDIC CHANNELS
`
`(57)
`
`ABSTRACT
`
`(76)
`
`Inventors: Horst Haussecker, Palo Alto, CA (US);
`Narayan Sundararajan, San Francisco,
`CA (US)
`
`Correspondence Address:
`MARSHALL, GERSTEIN & BORUN LLP
`6300 SEARS TOWER
`233 8S. WACKER DRIVE
`CHICAGO,IL 60606 (US)
`
`(21) Appl. No.:
`
` 10/232,170
`
`(22)
`
`Filed:
`
`Aug. 30, 2002
`
`Publication Classification
`
`TMGAGS nacicecnsccna GOIN 1/10
`(SY)
`(52) US. Cheeee 436/180; 436/52; 422/100;
`422/81
`
`Disclosed herein is an apparatus that includes a body struc-
`ture having a plurality of microfluidic channels fabricated
`therein, the plurality of microfluidic channels comprising a
`center channel and focusing channels in fluid communica-
`tion with the center channel via a plurality of cascaded
`junctions. Also disclosed herein is a methodthat includes the
`step of providing a body structure having a plurality of
`microfluidic channels fabricated therein,
`the plurality of
`microfluidic channels comprising a center channel and
`focusing channels in fluid communication with the center
`channel via a plurality of cascaded junctions. The method
`also includes the steps of providing a flow of the sample
`fluid within the center channel, providing flows of sheath
`fluid in the focusing channels, and controlling or focusing
`the flow ofthe sample fluid by adjusting the rate at which the
`sheath fluid flows through the focusing channels and cas-
`caded junctions, and into the center channel. The disclosed
`apparatus and method can be useful to control or to focus a
`flow of a sample fluid in a microfluidic process are dis-
`closed. Additionally, the apparatus and method canbe useful
`to detect molecules ofinterest in a microfluidic process.
`
`
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 1
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 1
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`Patent Application Publication Mar. 4, 2004 Sheet 1 of 3
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`US 2004/0043506 Al
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`ABS Global, Inc. and Genus plc – Ex. 1015, p. 2
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 2
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`

`

`Patent Application Publication
`
`Mar.4, 2004 Sheet 2 of 3
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`US 2004/0043506 Al
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`
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`ABS Global, Inc. and Genus plc – Ex. 1015, p. 3
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 3
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`

`

`Sheet 3 of 3
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`US 2004/0043506 Al
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`Mar.4, 2004
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`Patent Application Publication
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`ABS Global, Inc. and Genus plc – Ex. 1015, p. 4
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 4
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`

`

`US 2004/0043506 Al
`
`Mar. 4, 2004
`
`CASCADED HYDRODYNAMIC FOCUSING IN
`MICROFLUIDIC CHANNELS
`
`BACKGROUND OF THE DISCLOSURE
`
`[0001]
`
`1. Field of the Invention
`
`[0002] The invention generally relates to fluid transport
`phenomena and, more specifically,
`to the control of fluid
`flow in microfluidic systems and precise localization of
`particles/molecules within such fluid flows.
`
`[0003]
`
`2. Brief Description of Related Technology
`
`[0004] Miniaturization of a variety of laboratory analyses
`and functions provides a number of benefits such as, for
`example, providing substantial savings in time and cost of
`analyses, and space requirements for the instruments per-
`forming the analyses. Such miniaturization can be embodied
`in microfluidic systems. These systems are useful in chemi-
`cal and biological research such as, for example, DNA
`sequencing and immunochromatography techniques, blood
`analysis, and identification and synthesis of a wide range of
`chemical and biological species. More specifically,
`these
`systems have been used in the separation and transport of
`biological macromolecules,
`in the performance of assays
`(e.g., enzyme assays,
`immunoassays,
`receptor binding
`assays, and other assays in screening for affectors of bio-
`chemical systems).
`
`[0005] Generally, microfluidic processes and apparatus
`typically employ microscopic channels through which vari-
`ous fluids are transported. Within these processes and appa-
`ratus, the fluids may be mixed with additional fluids, sub-
`jected
`to
`changes
`in
`temperature,
`pH,
`and
`ionic
`concentration, and separated into constituent elements. Still
`further, these apparatus and processes also are useful in other
`technologies, such as, for example, in ink-jet printing tech-
`nology. The adaptability of microfluidic processes and appa-
`ratus can provide additional savings associated with the
`costs of the human factor of (or error in) performing the
`same analysesor functions such as, for example, labor costs
`and the costs associated with error and/or imperfection of
`human operations.
`
`(0006] The ability to carry out these complex analyses and
`functions can be affected by the rate and efficiency with
`which these fluids are transported within a microfluidic
`system. Specifically, the rate at which the fluids flow within
`these systems affects the parameters upon which the results
`of the analyses may depend. For example, when a fluid
`contains molecules, the size and structure of whichare to be
`analyzed, the system should be designed to ensure that the
`fluid is transporting the subject molecules in an orderly
`fashion through a detection device at a flowrate such that the
`device can perform the necessary size and structural analy-
`ses. There are a variety of features that can be incorporated
`into the design of microfluidic systems to ensure the desired
`flow is achieved. Specifically, fluid can be transported by
`internal or external pressure sources, such as integrated
`micropumps, and by use of mechanical valves to re-direct
`fluids. Utilization of acoustic energy, electrohydrodynamic
`energy, and other electrical means to effect fluid movement
`also have been contemplated. Each, however, suffers from
`certain disadvantages, most notably malfunction. Addition-
`ally, the presence ofeach in a microfluidic system addsto the
`cost of the system.
`
`[0007] Microfluidic systems typically include multiple
`microfluidic channels interconnected to (and in fluid com-
`munication with) one another and to one or more fluid
`reservoirs. Such systems may be very simple, including only
`one or two channels and reservoirs, or may be quile com-
`plex, including numerous channels and reservoirs. Microf-
`luidic channels generally have at least one internal trans-
`verse dimensionthatis less than about one millimeter (mm),
`typically ranging from about 0.1 micrometers (4m) to about
`500 um. Axial dimensions of these micro transport channels
`may reach to 10 centimeters (cm) or more.
`
`(0008] Generally, a microfluidic system includes a net-
`work of microfluidic channels and reservoirs constructed on
`a planar substrate by etching, injection molding, embossing,
`or stamping. Lithographic and chemical etching processes
`developed by the microelectronics industry are used rou-
`tinely to fabricate microfluidic apparatus on silicon and glass
`substrates. Similar etching processes also can be used to
`construct microfluidic apparatus on various polymeric sub-
`strates as well. After construction of the network of microf-
`luidic channels and reservoirs on the planar substrate, the
`substrate typically is mated with one or more planar sheets
`that seal channel and reservoir tops and/or bottoms while
`providing access holes for fluid injection and extraction
`ports as well as electrical connections, depending upon the
`end use of the apparatus.
`
`BRIEF DESCRIPTION OF THE DRAWING
`FIGURES
`
`For a more complete understanding ofthe disclo-
`(0009]
`sure, reference should be made to the following detailed
`description and accompanying drawings wherein:
`[0010] FIG. 1 schematically illustrates a partial cross-
`section of an enlarged microfluidic apparatus exemplifying
`single-step (non-cascading), hydrodynamic fluid focusing;
`
`(0011] FIG. 2 schematically illustrates a partial cross-
`section of an enlarged microfluidic apparatus exemplifying
`multi-step (cascading), hydrodynamic fluid focusing accord-
`ing to the disclosure; and,
`[0012] FIG. 3 schematically illustrates a partial cross-
`section of an enlarged microfluidic apparatus exemplifying
`multi-step (cascading), hydrodynamicfluid focusing accord-
`ing to the disclosure.
`
`[0013] While the disclosed method and apparatus are
`susceptible of embodiments in various forms,
`there are
`illustrated in the drawing figures (and will hereafter be
`described) specific embodiments of the disclosure, with the
`understanding that the disclosure is intended to be illustra-
`live, and is not intendedto limit the invention to the specific
`embodiments described and illustrated herein.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0014] As used herein, the term (or prefix) “micro” gen-
`erally refers to structural elements or features of an appa-
`ratus or a component thereof having at least one fabricated
`dimension in a range of about 0.1 micrometer (sm) to about
`500 um. Thus, for example, an apparatus or process referred
`to herein as being microfluidic will
`include at
`least one
`structural feature having such a dimension. When used to
`describe a fluidic element, such as a channel, junction, or
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 5
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 5
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`US 2004/0043506 Al
`
`Mar. 4, 2004
`
`reservoir, the term “microfluidic” generally refers to one or
`more fluidic elements (¢.g., channels, junctions, and reser-
`voirs) having at least one internal cross-sectional dimension
`(e.g., depth, width, length, and diameter), that is less than
`about 500 um, and typically between about 0.1 um and about
`500 wm.
`
`[0015] The term “hydraulic diameter” as used herein
`refers to a diameter as defined in Table 5-8 of Perry's
`Chemical Engineers’ Handbook, 6" ed., at p. 5-25 (1984).
`See also, Perry's Chemical Engineers’ Handbook, 7th ed. at
`pp. 6-12 to 6-13 (1997). Such a definition accounts for
`channels having a non-circular cross section or for open
`channels, and also accounts for low through an annulus.
`
`[0016] As knownby those skilled in the art, a Reynolds
`number (Nx) is any of several dimensionless quantities of
`the form:
`
`[0017] which are all proportional to the ratio of inertial
`force to viscous force in a flow system. Specifically, I is a
`characteristic linear dimension ofthe flow channel, v is the
`linear velocity, p is the fluid density, and w#
`is the fluid
`viscosity. Also known by those skilled in the art is the term
`“streamline,” which defines a line whichlies in the direction
`of flow at every point at a given instant. The term “laminar
`flow” defines a flow in which the streamlines remain distinct
`from one another over their entire length. The streamlines
`need not be straight or the flow steady as long as this
`criterion is fulfilled. See generally, Perry's Chemical Engi-
`neers’ Handbook, 6" ed., a p. 5-6 (1984). Generally, where
`the Reynolds numberis less than or equal to 2100, the flow
`is presumed to be laminar, and where the Reynolds number
`exceeds 2100, the flow is presumed to be non-laminar(i.e.,
`turbulent). Preferably,
`the Hows of fluid throughout
`the
`various microfluidic processes and apparatus herein are
`laminar.
`
`second focusing channels 14 and 16, respectively, and
`through the junction 18 at a velocity of v,,. Because the
`velocity of the flows of sheath fluid are identical, and
`depending upon the densities and viscosities of the sheath
`and sample fluids, the flows of sheath fluid entering the
`center channel 12 through the junction 18 combine to form
`a discrete sheath 24 around the flow of sample fluid. The
`discreteness of the sheath 24 is ensured where, as noted
`above, the flows of fluid are laminar. Downstream of the
`junction 18,
`the sample fluid flows through the center
`channel 12 at the same flowrate, but a different (and higher)
`velocity of v,, and occupies a
`region therein generally
`having a hydraulic diameter of d,. The flows of sheath fluid
`from thefirst and secondreservoirs 20 and 22, respectively,
`combine to form the sheath 24 around the sample fluid (an
`outline of which is depicted by the continuous, dashed
`streamline within the center channel 12).
`
`[0020] Generally, the single-step (non-cascading) hydro-
`dynamic focusing shown in FIG, 1 is accomplished by the
`three-way junction 18 when sheath fluid from the focusing
`channels 14 and 16 pushes the sample fluid in the center
`channel 12 more closer to the center axis of the center
`channel 12, while increasing the velocity of the sample fluid
`through the channel 12 from v,
`to v5. This focusing is
`represented in FIG. 1 by the continuous, dashedlines within
`the center channel 12. Any particles (or molecules) sus-
`pendedin the sample fluid of the center channel 12 upstream
`of the junction 18, migrate towards the center axis of the
`channel 12 as the fluid flows through and past the junction
`18. Spacial localization of the particles (or molecules) can be
`controlled and focused in this manner and analyzed or
`manipulated in downstream operations.
`
`(0021] The maximum achievable focusing ratio in a single
`focusing step is limited by hydrodynamic and geometric
`constrains that
`follow an asymptotic relationship. More
`specifically, the focusing ratio (f,) can be expressed by the
`following equation, where d, and d, are hydraulic diameters
`as described above:
`
`(0018] Referring now to the drawing figures wherein like
`reference numbers represent the same or similar elements in
`the variousfigures, FIG. 1 schematically illustrates a partial
`cross-section of an enlarged microfluidic apparatus exem-
`plifying single-step (non-cascading), hydrodynamic fluid
`focusing. The apparatus is a body structure 10 having a
`center channel 12, and symmetric,first and second focusing
`channels 14 and 16, respectively, in fluid communication
`with the center channel 12 via a junction 18. As shown in
`FIG, 1, the first focusing channel 14 is in fluid communi-
`cation with a first reservoir 20 and the second focusing
`channel 16 is in fluid communication with a second reservoir
`22. Solid arrows indicate the direction of flow through the
`various channels 12, 14, and 16.
`
`Ideally, a high focusing ratio is desired. For a single
`[0022]
`focusing step, however, this ratio is subject to limitations,
`such as those imposed by hydrodynamicseffects, pressure
`gradients, and channel dimensions. For example, as pressure
`in the focusing channels increases, the flow in the center
`channel is susceptive to back flow. In other words, depend-
`ing upon the flow rate in the center channel upstream of the
`junction,
`if the flowrate of (or pressure exerted by)
`the
`sheath fluid in the focusing channels is too great, the sheath
`fluid will flow into, not only that portion of the center
`channel downstream of the junction, but also into portions of
`the center channel that are upstream of the junction; thus,
`[0019] As shown,the center channel 12 hasafixed, inner
`effectively causing a backwards flow of the sample fluid.
`diameter denoted as d_. Upstream of the junction 18, a
`sample fluid flows through the center channel 12 at a
`velocity of v; and occupies a region therein generally having
`a hydraulic diameter of d; defined by the inner walls of the
`center channel 12. Upstream of the junction 18, d; is iden-
`tical
`to d.. Sheath fluid flows from the first and second
`reservoirs 20 and 22, respectively,
`through the first and
`
`It has been discovered that such limitations can be
`[0023]
`overcome by utilizing multiple (or multi-step), cascaded
`junctions whereby the sample fluid is incrementally focused
`at each successive junction. Specifically, FIGS. 2 and 3
`schematically illustrate partial cross-sections of enlarged
`microfluidic apparatus exemplifying multi-step (cascading),
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 6
`ABS Global, Inc. and Genus plc — Ex. 1015, p. 6
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`US 2004/0043506 Al
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`Mar. 4, 2004
`
`hydrodynamic fluid focusing. Specifically, in FIG, 2, the
`apparatus is a body structure 28 having a center channel 30,
`and symmetric, first and second focusing channels 32 and
`34, respectively,
`in fluid communication with the center
`channel 30 via a first junction 36, As shown in FIG,2, the
`first focusing channel 32 is in fluid communication with a
`first reservoir 38, and the second focusing channel 34 is in
`fluid communication with a second reservoir 40. Solid
`arrows indicate the direction of flow through the various
`channels 30, 32, and 34.
`
`[0024] As shown, the center channel 30 has a fixed, inner
`diameter denoted as d,. Upstream of the junction 36, a
`sample fluid flows from a reservoir (not shown) and through
`the center channel 30 at a velocity of v, and occupies a
`region therein generally having a hydraulic diameter of d,
`defined by the inner wall of the center channel 30. Upstream
`of the junction 36, d, is identical to d.. Sheath fluid flows
`from the reservoirs 38 and 40, through the focusing channels
`32 and34, and through the first junction 36 at a velocity of
`V,,- Because the velocity of the flows of sheath fluid are
`identical, and depending upon the densities and viscosities
`of the sheath and sample fluids, the flows of sheath fluid
`entering the center channel 30 through thefirst junction 36
`combine to form a discrete, first sheath 42 around the flow
`of sample fluid. The discreteness of the first sheath 42 is
`ensured where, as noted above,
`the flows of fluid are
`laminar. Downstream of the first junction 36, the sample
`fluid flows through the center channel 30 at
`the same
`flowrate, but a different (and higher) velocity of v,, and
`occupies a region therein generally having a hydraulic
`diameter of d,. The flows of sheath fluid from the first and
`second reservoirs 38 and 40, respectively, combine to form
`the first sheath 42 around the sample fluid (an outline of
`which is depicted by the continuous, dashed streamline
`within the center channel 30).
`
`[0025] Asecond junction 44 downstream (in the direction
`of flow ofthe sample fluid in the center channel 30) of the
`first junction 36 communicates additional sheath fluid from
`symmetric, third and fourth focusing channels 46 and 48,
`respectively,
`into the center channel 30, which already
`contains the sample fluid surroundedbythefirst sheath 42.
`As shown in FIG. 2, the third focusing channel 46is in fluid
`communication with a third reservoir 50, and the fourth
`focusing channel 48is in fluid communication with a fourth
`reservoir 52. Solid arrows indicate the direction of flow
`through the various channels 30, 46, and 48.
`
`[0026] Downstream of the first junction 36 and upstream
`ofthe second junction 44, the sample fluid ows through the
`center channel 30 at the same flowrate, but a different (and
`higher) velocity of v,, and occupies a region therein gener-
`ally having a hydraulic diameter of d,. Sheath fluid flows
`from the third and fourth reservoirs 50 and 52, respectively,
`through the third and fourth focusing channels 46 and 48,
`respectively, and through the second junction 44 at a veloc-
`ity of v,,. Because the velocity of the flows of sheath fluid
`are identical, and depending upon the densities and viscasi-
`ues of the sheath and sample fluids, the flows of sheath fluid
`entering the center channel 30 through the secondjunction
`44 combine to form a second, discrete sheath 54 around the
`flow of the sample fluid and thefirst sheath 42. The flows of
`sheath fluid from the third and fourth reservoirs 50 and 52,
`respectively, combine to form the second sheath 54 around
`
`the sample fluid (an outline of which is depicted by the
`continuous, dashed streamline within the center channel 30).
`
`‘Together, the first and second junctions 36 and 44,
`(0027]
`respectively, and the focusing channels (32, 34, 46, and 48)
`that communicate with the center channel 30 via these
`junctions encompass an embodiment of a multi-step (cas-
`cading), hydrodynamic fluid focusing method and appara-
`tus—specilically two focusing steps or junctions. As shown
`in FIG. 2, the apparatus can include additional focusing
`channels 56 and 58 capable of communicating additional
`sheath fluid via additional junction(s) 60 to the center
`channel 30. Similarly,
`these additional focusing channels
`communicate with additional reservoirs 62 and 64, which
`can be a source for the additional sheath fluid. To control
`each focusing step (f,), individually, in an apparatus such as
`the one shownin FIG,2, the pressure in each reservoir (38,
`40, 50, 52, 62, and 64) can be adjusted to yield the desired
`flow rate of sheath fluid within the communicating channels
`(32, 34, 46, 48, 56, and 58, respectively).
`
`[0028] FIG. 3 schematically illustrates a partial cross-
`section of an enlarged microfluidic apparatus exemplifying
`multi-step (cascading), hydrodynamic fluid focusing. Gen-
`erally, this embodiment is similarto that illustrated in FIG.
`2, however, in FIG. 3, the apparatus is a body structure 66
`containing focusing channels that draw sheath fluid from
`fewer (and common)reservoirs 68 and 70. Similar to FIG.
`2, however, FIG, 3 also is capable of providing incremental,
`hydrodynamic fluid focusing. To control each focusing step
`(f,), individually, in an apparatus such as the one shownin
`FIG. 3, where all (or many) of the focusing channels are
`communicating with a single reservoir, the dimensions of
`the individual focusing channels communicating with the
`single reservoir can be designed to yield the desired flow rate
`of sheath fluid within those communicating channels.
`
`In an apparatus, such as the ones shown in FIGS.
`[0029]
`2 and 3, the total focusing ratio (f,) accomplished by n
`focusing steps (or junctions) can be derived by the following
`equation, where f; denotes each individual focusing step:
`
`tual
`
`d, - d, dz
`dy,
`i. ay ds
`
`
`
`.
`di
`dint) [|
`dy “3 Font |
`
`[0030] The focusing ratio of each particular focusing step
`(f,) can be adjusted by controlling the flow rate of sheath
`fluid entering the center channel at the corresponding junc-
`tion. Alternatively,
`the focusing ratio of each particular
`focusing step (f;) can be adjusted by controlling the pressure
`exerted by the sheath fluid on the sample fluid as the sheath
`fluid enters the center channel at the corresponding junction.
`
`For n focusing steps (or junctions) each commu-
`{0031]
`nicating with focusing channels having diameters of dy.;,
`connectedto a single pair of reservoirs 68 and 70 (see FIG.
`3), the foregoing equation reduces to:
`fn=(fe)"
`
`[0032] which monotonically increases for f,>1.
`
`[0033] The distances between the successive junctions
`need not be identical and can be determined by those skilled
`in the art based upon the intended application. Similarly, the
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 7
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 7
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`US 2004/0043506 Al
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`Mar. 4, 2004
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`lengths and hydraulic diameters of the various microfluidic
`channels need not be identical
`to one another and can be
`determined based upon the intended application by those
`skilled in the art.
`
`{0034] As a result of the conservation law of laminar
`flows, the velocity of the sample fluid increases after each
`successive junction. In order to avoid exceeding the maxi-
`mum allowable fluid velocity,
`the apparatus and method
`should be designed by considering the velocities of the input
`flow (having a velocity of v,, as in FIGS. 2 and 3, for
`example) and focusing flows (havinga velocities of v,,, V,.5
`and v,, as in FIGS, 2 and 3, for example). In the situation
`where a microfluidic system is used for single-molecule
`detection (¢.g., molecules of interest in genomic or DNA
`sequencing techniques) in a downstream detection device,
`the foregoing focusing effects can be used to incrementally
`stretch inter-molecule distances within the sample (mol-
`ecule-carrying) fluid. Starting with very narrow spacing of
`adjacent molecules, the molecules can be spaced apart at
`increasing distances as the sample (molecule-carrying) liq-
`uid passes each successive focusing slep, to a point where
`the molecules are sufficiently spaced apart to permit rapid
`and accurate detection by the detection device. This is but
`one way in which hydrodynamic focusing using multiple
`cascaded junctions can be useful in microfluidic systems.
`
`[0035] Even though laminar flowsof fluid are preferred, as
`previously noted, diffusional effects may be present even
`with such laminar flows. Specifically, diffusional effects may
`be realized as the time period in which a sheath fluid spends
`in contact with the sample fluid increases. The realized effect
`can be demonstrated by way of example, wherein a sample
`fluid contains ten molecules of interest. As this sample fluid
`flows through the center channel and comes into contact
`with a sheath fluid, its flow will be controlled (or focused).
`Though the flows of both fluids may be laminar, as the
`length oftime that the sheath and sample fluid are in contact
`with one another increases, diffusional forces will cause
`someof the ten molecules of interest to diffuse from the flow
`sample fluid into the flow sheath fluid. These diffusional
`forces may be controlled by, for example, adjusting the fluid
`flows, adjusting the time period that the sample fluid spends
`in contact with the sheath fluid, selection of appropriate
`sheath fluids, and/or adjusting the length of the center
`channel. In certain applications, the effects of diffusion may
`be desired (useful), whereas in other applications, such
`effects may not be desired. For example, these diffusional
`effects may be useful to obtain a fluid detection volume
`where only a single molecule of interest resides,
`
`[0036] The hydraulic diameter of each of the microfluidic
`channels preferably is about 0.01 #m to about 500 am,
`highly preferably about 0.1 wm and 200 wm, more highly
`preferably about
`1 wm to about 100 wm, even more highly
`preferably about 5 4m to about 20 wm. The various focusing
`channels (32, 34, 46, 48, 56, and 58) can have the same or
`different hydraulic diameters. Preferably, symmetric focus-
`ing channels have equal or substantially equal size hydraulic
`diameters, Depending upon the particular application, the
`various focusing channels may have hydraulic diameters
`that are less than (or greater than) the hydraulic diameter of
`the center channel.
`
`(0037] Generally, the sheath fluid flows through the focus-
`ing channels and cascaded junctions at different Howrates
`
`relative to each other. However, preferably, the flows of fluid
`through symmetric focusing channels are equal or substan-
`tially equal. Furthermore, the sheath fluid can flow through
`the respective focusing channels and respective cascaded
`junctions al a flowrate greater than the rate at which fluid
`flows through the center channel immediately upstream of
`the respective junctions.
`[0038] The body structure of the microfluidic apparatus
`and method described herein typically includes an aggrega-
`tion of two or more separate substrates, which, when appro-
`priately mated or joined together, form the desired microf-
`luidie device, e.g., containing the channels and/or chambers
`described herein. Typically,
`the microfluidic apparatus
`described herein can include top and bottom substrate por-
`tions, and an interior portion, wherein the interior portion
`substantially defines the channels, junctions, and reservoirs
`of the apparatus.
`[0039] Suitable substrate materials include, but are not
`limited to, an elastomer, glass, a silicon-based material,
`quartz, fused silica, sapphire, polymeric material, and mix-
`tures thereof. The polymeric material may be a polymer or
`copolymer
`including, but not
`limited to, polymethyl-
`methacrylate (PMMA), polycarbonate, polytetrafluoroeth-
`ylene (e.g., TEFLON™), polyvinylchloride (PVC), poly-
`dimethylsiloxane
`(PDMS), polysulfone,
`and mixtures
`thereto. Such polymeric substrate materials are preferred for
`their ease of manufacture, low cost, and disposability, as
`well as their general inertness. Such substrates are readily
`manufactured using available microfabrication techniques
`and molding techniques, such as injection molding, emboss-
`ing or stamping, or by polymerizing a polymeric precursor
`material within the mold. The surfaces of the substrate may
`be treated with materials commonly used in microfluidic
`apparatus by those ofskill in the art to enhance various flow
`characteristics.
`
`[0040] Use of a plurality of cascaded junctions in the
`manner described herein results in microfluidic flow systems
`that do not need conventional flow control equipment, like
`internal or external pressure sources, such as integrated
`micropumps, or mechanical valves to re-direct the fluids.
`Utilization of acoustic energy, electrohydrodynamic energy,
`and other electrical meansto effect fluid movement also are
`not necessary when employing the plurality of cascaded
`junctions in the manner described herein. Without conven-
`tional equipment, there is less likelihood of system malfunc-
`tion and total costs associated with the operation and manu-
`facture of such systems.
`apparatus
`and
`processes
`[0041] The microfluidic
`described herein can be used asa part of a larger microfluidic
`system, such as in conjunction with instrumentation for
`monitoring fluid transport, detection instrumentation for
`detecting or sensing results of the operations performed by
`the system, processors, ¢.g., computers, for instructing the
`monitoring instrumentation in accordance with prepro-
`grammedinstructions, receiving data from the detection
`instrumentation, and for analyzing, storing and interpreting
`the data, and providing the data and interpretations in a
`readily accessible reporting format.
`[0042] The foregoing description is given for clearness of
`understanding only, and no unnecessary limitations should
`be understood therefrom, as modifications within the scope
`of the disclosure may be apparent to those having ordinary
`skill in the art.
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 8
`ABS Global, Inc. and Genusplc — Ex. 1015, p. 8
`
`

`

`US 2004/0043506 Al
`
`Mar. 4, 2004
`
`What is claimedis:
`1. An apparatus useful to control or to focus a flow of a
`sample fluid in a microfluidic process, the apparatus com-
`prising a body structure having a plurality of microfluidic
`channels fabricated therein,
`the plurality of microfluidic
`channels comprising a center channel and focusing channels
`in fluid communication with the center channel via a plu-
`rality of cascaded junctions.
`2. The apparatus of claim 1, wherein the center channel is
`in fluid communication with a reservoir containing the
`sample fluid.
`3. The apparatus of claim 1, wherein the focusing chan-
`nels are in fluid communication with one or more reservoirs,
`each reservoir containing a sheath fluid.
`4. The apparatus of claim 1, wherein the body structure is
`a material selected from the group consisting of an elas-
`tomer, glass, a silicon-based material, quartz, fused silica,
`sapphire, polymeric material, and mixtures thereof.
`5. The apparatus of claim 4, wherein the polymeric
`material is a polymer or copolymerselected from the group
`consisting of polymethylmethacrylate, polycarbonate, poly-
`tetrafluoroethylene, polyvinylchloride, polydimethylsilox-
`ane, polysulfone, and mixtures thereof.
`6. The apparatus of claim 1, wherein each of the microf-
`luidic channels has a hydraulic diameter and the hydraulic
`diameters of the focusing channels are all equal.
`7. The apparatus of claim 1, wherein each of the microf-
`luidic channels has a hydraulic diameter and the hydraulic
`diameter of each of the focusing channels is less than the
`hydraulic diameter of the center channel.
`8. The apparatus of claim 1, wherein each of the microf-
`luidic channels has a hydraulic diameter and the hydraulic
`diameter of each of the focusing channels is greater than the
`hydraulic diameter of the center channel.
`9. The apparatus of claim 1, wherein each of the microf-
`luidic channels has a hydraulic diameter of about 0.01
`micrometers (4m) to about 500 «am.
`10. The apparatus of claim 9, wherein the hydraulic
`diameter is about 0.1 wm and 200 um.
`11. The apparatus of claim 10, wherein the hydraulic
`diameter is about | wm to about 100 sm.
`12. The apparatus of claim 11, wherein the hydraulic
`diameter is about 5 wm to about 20 4m.
`13. A method useful to control or to focus a flow of a
`sample fluid in a microfluidic process, the method compris-
`ing the steps of:
`
`(a) providing a body structure having a plurality of
`microfluidic channels fabricated therein, the plurality
`of microfluidic channels comprising a center channel
`and focusing channels in fluid communication with the
`center channel via a plurality of cascaded junctions;
`
`(b) providing a flow of the sample fluid within the center
`channel;
`
`(c) providing flows of sheath fluid in the focusing chan-
`nels; and,
`
`(d) controlling or focusing the flow ofthe sample fluid by
`adjusting the rate at which the sheath fluid flows
`through the focusing channels and cascaded junctions,
`and into the center channel.
`
`14. The method ofclaim 13, wherein the flow of sample
`fluid