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`
`US 2{){l40tl435(lé/\1
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0043506 A1
`Hausseeker et at. Mar. 4, 2004 (43) Pub. Date:
`
`
`
`(54) CASCADE!) HYDRODYNAMIC FOCUSING
`IN MICROFLUIDIC CHANNELS
`
`(57)
`
`ABS’I‘RAC'I‘
`
`(76)
`
`Inventors: Hurst Haussccker, Palo Alto, CA (US);
`Namyan Stlndararajttn, San Francisco,
`CA (US)
`
`Correspondence A516“???
`MAR§HALBGER$1MN 8‘ BORUN LL?
`Egan’ssmlg'KriifivBlfiEVE
`‘
`‘
`:
`1
`.
`LHIC’AGO’ 11‘ 60606 (US)
`
`(21) Appl. No.:
`
`1093;170
`
`(22
`
`Filed:
`
`Aug. 30, 2002
`
`Publication Classification
`
`Int. Cl.7 ....................................................... G01N 1110
`(51)
`(52) U.S. Cl.
`............................ 4361180; 43652; 422,!100;
`422,581
`
`Disclosed herein is an apparatus that includes a body struc-
`turc having a plurality of microf‘luidic channels fabricated
`therein. the plurality of microftuidic 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 method that includes the
`step of providing a bodyr structure having a plurality of
`mierofluidic channels fabricated therein,
`the plurality of
`mierotluidic channels comprising a center channel and
`focusing channeLs in tluid communication with the center
`channel via a plurality of cascaded junctions. The method
`also includes the steps of providing a tlow of the sample
`
`fluid within the center channel, providing flows of sheath
`fluid in the focusing channels. and controlling or locusing
`the flow ot‘the sample fluid by adjusting the rate at which the
`sheath fluid flows through the focusing channels and eas-
`cadet! junctions, and into the center channel. The disclosed
`apparatus and method can be useful to control or to focus a
`[low of a sample fluid in a microlluidic process are dis-
`closed. Additionally, the apparatus and method can be useful
`to detect molecules of interest in a microlluidic process.
`
`I
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`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 1
`ABS Global, Inc. and Genus plc — EX. 1015, p. 1
`
`

`

`Patent Application Publication Mar. 4, 2004 Sheet 1 0f 3
`
`US 2004/0043506 A1
`
`
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 2
`ABS Global, Inc. and Genus plc — EX. 1015, p. 2
`
`

`

`Patent Application Publication
`
`Mar. 4, 2004 Sheet 2 of 3
`
`US 2004/0043506 A1
`
`
`
`kN.wE
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 3
`ABS Global, Inc. and Genus plc — EX. 1015, p. 3
`
`

`

`Patent Application Publication
`
`Mar. 4, 2004 Sheet 3 0f 3
`
`US 2004/0043506 A]
`
`J
`
`r%/////////////4
`
`V\V\\\\\\\\\\\\\\§
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 4
`ABS Global, Inc. and Genus plc — EX. 1015, p. 4
`
`
`
`

`

`US 2004/0043506 A1
`
`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 micmfluidic systems and precise localization of
`particleslmolecules within such fluid flows.
`
`[0003]
`
`2. Brief Description of Related 'l‘echnology
`
`[0004] Miniaturization of a varietyr 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 tnicrofluidic 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 lluids 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
`cash; of the human factor of (or error in) performing the
`same analyses or functions such as. for example, labor costs
`and the costs associated with error andlor imperfection of
`human operations.
`
`[0006] The ability to carry out these complex analyses and
`functions can be alIected by the rate and eflicieney 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 which are 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 llowrate 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 elfect fluid movement
`also have been contemplated. Each, however, suffers from
`certain disadvantages, most notably malfunction. Addition-
`ally, the presence ofeach in a microlluidic system adds to the
`cost of the system.
`
`[0007] Microfiuidic 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 quite com-
`plex, including numerous channels and reservoirs. Microf—
`luidic channels generally have at least one internal trans-
`verse dimension that is less than about one millimeter (mm),
`typically ranging from about 0.] micrometers (pm) 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 nou-
`tinely to fabricate microfluidie 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 andfor 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 of the disclo-
`[0009]
`sure, reference should he made to the following detailed
`description and accompanying drawings wherein:
`
`[0010] FIG. 1 schematically illustrates a partial cross—
`section of an enlarged microlluidic apparatus exemplifying
`single-step {non-cascading). hydrodynamic fluid focusing;
`
`[0011] FIG. 2 schematically illustrates a partial cross-
`section of an enlarged microlluidic 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
`mu lti-step (cascading), hydrodynamic fluid focusing acmrd-
`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 illustrafi
`live, and is not intended to 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 (rim) 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 Genus plc — EX. 1015, p. 5
`
`

`

`US 2004/0043506 A1
`
`Mar. 4, 2004
`
`reservoir, the term "microfluidic" generally refers to one or
`more fluidic elements (cg, channels, junctions, and reser-
`voirs) having at least one internal cross-sectional dimension
`(cg, depth, width, length, and diameter), that is less than
`about 500 lrim, and typically between about 0.1 pm and about
`500 pm.
`
`[0015] The term “hydraulic diameter" as used herein
`refers to a diameter as defined in Table 5-8 of Perry's
`Circtrticrri Engineers" Handbook, 6‘“ ed, at p. 5-25 (1984).
`See also, Perry ‘5 Chemical Engineers" Handbook, 7th ed. at
`pp. 6-12 to 6-1.3 (1997). Such a definition accounts for
`channels having a non-circular cross section or for open
`channels, and also accounts for flow through an annulus.
`
`[0016] As known by those skilled in the art, a Reynolds
`number (NRC) is any of several dimensionless quantities of
`the form:
`
`ivpHr-—.
`
`[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 of the flow channel, v is the
`linear velocity, p is the fluid density, and ,u is the fluid
`viscosity. Also known by those skilled in the art is the term
`"streamline," which defines a line which lies 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 '5 Chemical Engi—
`neer-5' Handbook, 6”I ed., at p. 5-6 (1984). Generally, where
`the Reynolds number is 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 flows of fluid throughout
`the
`various microlluidic processes and apparatus herein are
`laminar.
`
`[0018] Referring now to the drawing figures wherein like
`reference numbers represent the same or similar elements in
`the various figures, 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.
`
`[0019] As shown, the center channel 12 has a fixed, inner
`diameter denoted as do. Upstream of the junction 18, a
`sample fluid flows through the center channel 12 at a
`velocity of vi and occupies a region therein generally having
`a hydraulic diameter of di defined by the inner walls of the
`center channel 12. Upstream of the junction 18, d,- is iden-
`tical
`to dc. Sheath fluid flows from the first and second
`reservoirs 20 and 22. respectively,
`through the first and
`
`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 HOWs 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 diflerent {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 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 v1 to v2. This focusing is
`represented in FIG. 1 by the continuous, dashed lines within
`the center channel 12. Any particles (or molecules) sus-
`pended in 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 (is) can be expressed by the
`following equation, where 1:11 and (.12 are hydraulic diameters
`as described above:
`
`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 hydrodynamics effects, pressure
`gradients, and channel dimensions. For example, as pressure
`in the focusing channels increases, the [low 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 llu id in the focusing channels is too great, the sheath
`fluid will flow into, not only that portion of the center
`channel downstream of thejunction, but also into portionsof
`the center channel that are upstream of the junction; thus,
`ctl‘ectively causing a backwards flow of the sample fluid.
`
`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 mu [ti-step (cascading),
`
`ABS Global, Inc. and Genus plc – Ex. 1015, p. 6
`ABS Global, Inc. and Genus plc — EX. 1015, p. 6
`
`

`

`US 2004/0043506 A1
`
`Mar. 4, 2004
`
`LA
`
`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 dc. 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 d1
`defined by the inner wall of the center channel 30. Upstream
`of the junction 36, (:11 is identical to dc. Sheath fluid flows
`from the reservoirs 38 and 40, through the focusing channels
`32 and 34, and through the first junction 36 at a velocity of
`vd. 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 the first 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
`flowrale, but a different (and higher) velocity of v3, and
`occupies a region therein generally having a hydraulic
`diameter of (is. 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] A second junction 44 downstream {in the direction
`of flow of the 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 surrounded by the first sheath 42.
`As shown in FIG. 2, the third fecusing channel 46 is in fluid
`communication with a third reservoir 50, and the fourth
`focusing channel 48 is 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
`of the second junction 44, the sample fluid flows through the
`center channel 30 at the same flowrate, but a ditferent (and
`higher) velocity of v2, and occupies a region therein gener-
`afly having a hydraulic diameter of d2. 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 vlg. Because the velocity of the flows of sheath fluid
`are identical, and depending upon the densities and viscosi-
`ties of the sheath and sample fluids, the flows of sheath fluid
`entering the center channel 30 through the second junction
`44 combine to form a second, discrete sheath 54 around the
`flow of the sample fluid and the first 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).
`
`[0027] Together, the first and second junctions 36 and 44,
`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 lluid focusing method and appara-
`tus—specifically 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 ([5), individually, in an apparatus such as
`the one shown in 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 microlluidic apparatus exemplifying
`multi—step (cascading), hydrodynamic fluid focusing. (jen-
`erally, this embodiment is similar to 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
`(f5), individually, in an apparatus such as the one shown in
`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 (fn) accomplished by n
`focusing steps (or junctions) can be derived by the following
`equation, where fi denotes each individual focusing step:
`
`1;: fl = as
`03:
`d2 0'3
`
`
`"is” = 1—] inn
`dz:
`_l dour-=1
`
`[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 dig,
`connected to a single pair of reservoirs 68 and 70 (see FIG.
`3), the foregoing equation reduces to:
`Leila".
`
`[0032] which monotonically increases for f9].
`
`[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 Genus plc — EX. 1015, p. 7
`
`

`

`US 2004/0043506 A1
`
`Mar. 4, 2004
`
`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 allowahle fluid velocity,
`the apparatus and method
`should he 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 {having at velocities of vu, vrz,
`and vi, as in FIGS. 2 and 3, for example). In the situation
`where a microlluidic system is used for single-molecule
`detection (e.g., molecules of interest in genomic or DNA
`sequencing techniques) in a downstream detection device,
`the foregoing focusing elIects 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 step, 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 microlluidic systems.
`
`[0035] Even though laminar flows of fluid are preferred, as
`previously noted, ditIusionat effects may be present even
`with such laminar flows. Specifically, diffusional efiects 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 ot‘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 of time that the sheath and sample fluid are in contact
`with one another increases, diffusional forces will cause
`some ofthe ten molecules of interest to dilfuse from the flow
`sample tluid 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, andi'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 rliflusional
`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 rim to about 500 pm,
`highly preferably about 0.1 pm and 200 rim, more highly
`preferably about
`1 jinn to about 100 lmo, even more highly
`preferably about 5 rim to about 20 ,trm. 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 flowrates
`
`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 at 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—
`luidic device, cg, containing the channels andz'or chambers
`described herein.
`‘I'ypically,
`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.
`include, but are not
`[0039] Suitable substrate materials.
`limited to, art 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., TEFLONT”), polyvinylchloride (PVC), poly-
`dimethylsiloxane
`(PDMS), polysulfone,
`and mixtures
`thereto. Such polymeric substrate materials are preferred for
`their case 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 of skill in the art to enhance various flow
`characteristics.
`
`[0040] Use of a plurality of cascaded junctions in the
`manner described herein results in microlluidic flow systems
`that do not need conventional flow control equipment, like
`internal or external pressure sources, such as integrated
`micropumps, or mechanical valves to redirect the fluids.
`Utilization of acoustic energy, electrohydrodynamic energy,
`and other electrical means to 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 as a 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, e.g., computers, for instructing the
`monitoring instrumentation in accordance with prepro-
`grammed instructions, 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 Genus plc — EX. 1015, p. 8
`
`

`

`US 2004/0043506 A1
`
`Mar. 4, 2004
`
`What is claimed is:
`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 ofclaim 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 copolymer selected from the group
`consisting of polymethylmelhacrylate, polycarbonate, poly-
`tetrafluoroethylcnc, 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 l, 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 (pm) to about 500 ‘trm.
`10. The apparatus of claim 9, wherein the hydraulic
`diameter is about 0.] am and 200 ,nm.
`11. The apparatus of claim 10, wherein the hydraulic
`diameter is about 1 pm to about lOO rim.
`12. The apparatus of claim 11, wherein the hydraulic
`diameter is about 5 pm to about 20 ,um.
`13. A method useful to control or to focus a flow of a
`sample fluid in a rnicrofluidic process, the method compris-
`ing the steps of:
`
`(a) providing a body structure having a plurality of
`microfluidic channels fabricated therein, the pluralit