Apparatus and method for transferring liquids

The present invention concerns devices, apparatus and methods for transferring liquids. One aspect of the present invention is a device comprising a plate having a plurality of transfer elements. Each of the transfer elements comprises an aperture in the plate where the aperture is capable of being electrically activated. The plate has one of more attaching elements for attaching the plate to a multiwell plate to form a sealed system except for the apertures of the transfer elements. Usually, the device is adapted for sealing attachment to a multiwell plate. In a method in accordance with the present invention a quantity of liquid is disposed to a second side of a plate having a plurality of apertures in the plate. The apertures are capable of being electrically activated. The liquid is present in a closed well except for the apertures in the plate. To simultaneously expel liquid from the apertures, the apertures are electrically activated. Also disclosed are kits comprising a device in accordance with the present invention.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates generally to methods and apparatus employing a
 plurality of transfer elements for multiplexing transfer of droplets of
 sample from multiwell source plates to surfaces reservoirs such as in
 miniaturized cassettes, in which chemical syntheses and analyses are
 possible. The invention is useful for the generation of combinatorial
 libraries and high throughput screening in, for example, pharmaceutical
 drug discovery, agricultural pesticide discovery, genomic science
 applications and the like.
 2. Description of the Related Art
 In a range of technology-based business sectors, including the chemical,
 bioscience, biomedical, and pharmaceutical industries, it has become
 increasingly desirable to develop capabilities for rapidly and reliably
 carrying out chemical and biochemical reactions in large numbers using
 small quantities of samples and reagents. Carrying out a massive screening
 program manually, for example, can be exceedingly time consuming and may
 be entirely impracticable where only a very small quantity of an important
 sample or component of interest is available, or where a component of a
 synthesis or analysis is very costly.
 Accordingly, considerable resources have been directed to developing
 methods for high-throughput chemical syntheses, screening, and analyses.
 Considerable art has emerged, in part, from such efforts.
 Automated laboratory workstations have contributed significantly to
 advances in pharmaceutical drug discovery and genomic science over the
 past decade. See for example, U.S. Pat. Nos. 5,104,621 and 5,356,525
 (Beckman Instruments). More specifically, robotics technology has played a
 major role in providing a practical useful means for enabling high
 throughput screening (HTS) methods. Reference can be made, for example, to
 U.S. Pat. No. 4,965,049.
 In addition to the emergence of automation technology, the last decade has
 seen an enormous advance in the scientific understanding of critical
 cellular processes, and this has led to rationally designed approaches in
 drug discovery. Also, the application of molecular genetics and
 recombinant DNA technology, U.S. Pat. No. 4,237,224 (Cohen and Boyer), has
 led to the isolation of many genes encoding proteins, which show promise
 as targets for new drugs. Once a target gene is identified, the
 recombinant protein can be heterologously expressed in mammalian tissue
 culture cells, insect cells, bacteria and/or, yeast.
 The advantages of employing molecular cloning techniques are many. Often
 receptors and enzymes exist in alternative forms, subtypes or isoforms.
 Using a cloned target focuses the primary screen on the subtype
 appropriate for the disease. Agonists or antagonists can be identified and
 their selectivity can then be tested against the other known subtypes. The
 availability of such cloned genes and corresponding expression systems
 have enabled new types of screens to be created that are specific,
 sensitive, and often automatable.
 Matched with the scientific and technological advances in biology has been
 the emergence of innovative methods for highly parallel chemical
 synthesis. For several decades, preparation of synthetic analogs to the
 prototypic lead compound was the established method for drug discovery.
 Natural products were usually isolated from soil microbes and cultured
 under a wide variety of conditions. The spectrum of organisms employed by
 the pharmaceutical industry for isolation of natural products has now
 expanded from Actinomycetes and fungi to include plants, marine organisms,
 and insects.
 During the last five years, the chemistry of creating combinatorial
 libraries has made a vastly increased number of synthetic compounds
 available for testing. More specifically, thousands to tens or hundreds of
 thousands of small molecules can be rapidly and economically synthesized.
 See, for example, U.S. Pat. No. 5,252,743 (Affymax Technologies N.V.) for
 a discussion of combinatorial chemistry. Thus, combinatorial libraries
 complement the large numbers of synthetic compounds available from the
 more traditional drug discovery programs based, in part, on identifying
 lead compounds through natural product screening.
 Competitive binding assays, originally developed in the 1960's for
 immunodiagnostic applications, continue to be commonly employed for
 quantitatively characterizing receptor-ligand interactions. Despite
 advances in the development of spectrophotometric and fluorometric-based
 bioanalytical assays, radiolabeled ligands are still commonly employed in
 pharmaceutical HTS applications. Although non-isotopic markers promise to
 be environmentally cleaner, safer, less expensive, and generally easier to
 use than radioactive compounds, sensitivity limitations have prevented
 these new methods from becoming widespread. Another major disadvantage of
 the competition assay is the number of steps, most notably, washing steps,
 required to run the assays.
 A few years ago, Scintillation Proximity Assays were introduced by Amersham
 and also are discussed in U.S. Pat. Nos. 4,271,139 and 4,382,074 as a
 means of circumventing the wash steps required in the above heterogeneous
 assays. The new homogeneous assay technology, which requires no separation
 of bound from free ligand, is based on the coating of scintillant beads
 with an acceptor molecule, for example, the target receptor.
 Another variation of this theme avoids the use of radioactivity and is
 especially useful in high-throughput assays. The modification involves the
 use of lanthanide chelates in time-resolved fluorometry. Aspects of this
 particular homogeneous assay technology are discussed in U.S. Pat. No.
 5,637,509. This particular technology takes advantage of the unique
 properties of the lanthanide chelate europium-cryptate in combination with
 the energy absorbing molecule, allophycocyanin (APC).
 Robotic-based high-throughput tools are now routinely used for screening
 libraries of compounds for the purpose of identifying lead molecules for
 their therapeutic potential. Subsequently, considerable art has emerged.
 For example, a screening method for characterizing ligand binding to a
 given target employing a variety of separation techniques is described in
 the PCT application WO 97/01755. Another related method is described in
 U.S. Pat. No. 5,585,277 (Scriptgen Pharmaceuticals).
 Highly parallel and automated methods for DNA synthesis and sequencing have
 also contributed significantly to the success of the human genome project
 to date. For example, PE/Applied Biosystems (ABI), PerSeptive BioSystems,
 Pharmacia Biotech, and Beckman Instruments have developments in DNA
 synthesis instrumentation. In the area of DNA sequencing, ABI and LiCor
 are active. In addition, see U.S. Pat. No. 5,455,008. For a related
 invention, see Genzyme Corporation's HTS method for DNA analysis that is
 described in U.S. Pat. No. 5,589,330. For sequencing by hybridization, see
 PCT WO 89/10977 (Southern), Affymetrix (U.S. Pat. Nos. 5,599,695 and
 5,631,734), and U.S. Pat. No. 5,202,231 (Drmanac, et al.).
 Computerized data handling and analysis systems have also emerged with the
 commercial availability of high-throughput instrumentation for numerous
 life sciences research and development applications. Commercial software,
 including database and data management software, has become routine in
 order to efficiently handle the large amount of data being generated.
 Bioinformatics has emerged as an important field.
 With the developments outlined above in molecular and cellular biology,
 combined with advancements in combinatorial chemistry, there has been an
 exponential increase in the number of targets and compounds available for
 screening. In addition, many new genes and their expressed proteins will
 be identified by the Human Genome project and will therefore greatly
 expand the pool of new targets for drug discovery. Subsequently, an
 unprecedented interest has arisen in the development of more efficient
 ultrahigh throughput methods and instrumentation for pharmaceutical and
 genomic science screening applications.
 In recent parallel technological developments, miniaturization of chemical
 analysis systems, employing semiconductor processing methods, including
 photolithography and other wafer fabrication techniques borrowed from the
 microelectronics industry, has attracted increasing attention and has
 progressed rapidly. The so-called "lab-on-a-chip" technology enables
 sample preparation and analysis to be carried out on-board
 microfluidic-based cassettes. Moving fluids through a network of
 interconnecting enclosed microchannels of capillary dimensions is possible
 using electrokinetic transport methods.
 Application of microfluidics technology embodied in the form of analytical
 devices has many attractive features for pharmaceutical high throughput
 screening. Advantages of miniaturization include greatly increased
 throughput and reduced costs, in addition to low consumption of both
 sample and reagents and system portability. Implementation of these
 developments in microfluidics and laboratory automation hold great promise
 for contributing to advancements in life sciences research and
 development.
 Nonetheless, the 96 well microtiter plate and multiples thereof such as,
 e.g., the 384 well microtiter plate, have been, and still are, the
 pharmaceutical industry standard for carrying out bioanalytical assays
 despite the recent advances in miniaturization and microfluidics. Because
 an enormous number of synthetic libraries have been, and continue to be,
 generated using this particular multiwell format, the microtiter plate
 will remain entrenched within the industry.
 As microfluidic technologies advance, new methods for enabling fluid
 transfer between multi-well plates and microassay cassettes would be
 beneficial. A critical factor currently limiting such a microfluidic HTS
 hybrid device is a means for reproducible liquid communication between the
 disparate dimensions of the two systems. More specifically, integration of
 microfluidics technology with existing robotic-based methods currently
 used in automated workstations is constrained by differences in volume
 size of samples used. For these reasons, new automated methods for
 multiplexing common lab tasks such as sample handling and dispensing on
 the microscale are required. Once again, other parallel developments, in
 this case borrowed from the ink jet printing industry, are applicable to
 fulfilling, at least in part, this currently unmet technological need. The
 art is briefly reviewed.
 Various droplet ejector technologies have been or are being developed. One
 such technology, electrostatic discharge, is commonly used for dispensing
 fluids and reference may be made to U.S. Pat. Nos. 4,749,125; 5,086,973;
 5,165,601 issued to Terronics Development Corp.; and U.S. Pat. No.
 5,332,154 to Lundy and Associates.
 Other devices use electrostatic energy to eject ink onto a recording
 medium. For a more detailed description of electrostatic ink printing,
 reference may be made to U.S. Pat. No. 5,588,597 to MicroParts GmbH; U.S.
 Pat. No. 5,278,583 to Matsushita Electric Industrial Co.; U.S. Pat. No.
 4,915,718 to On Target Technology, Inc.; and U.S. Pat. No. 4,799,068 to
 Fuji Xerox Co., Ltd.
 Another related invention includes Quate's acoustic fluid ejector system as
 described in U.S. Pat. No. 5,608,433 issued to Xerox Corp. Other related
 U.S. Patents include U.S. Pat. No. 5,586,723 issued to Spraying Systems
 Co.; U.S. Pat. No. 5,164,740 issued to Yehuda Ivr, and the citations
 therein.
 Another ejector technology, piezoelectric ejection, is discussed in U.S.
 Pat. No. 5,164,740. For a more detailed description of piezoelectric
 printing, reference may be made to U.S. Pat. No. 5,529,055 issued to
 L'Oreal and the citations therein.
 An apparatus for liquid transfer has been made and used for delivering a
 plurality of samples in sequence to treatment reservoirs wherein a
 chemical reaction or physical treatment step occurs. See, e.g., U.S. Pat.
 No. 5,188,148 for a conduit plate for fluid delivery system and U.S. Pat.
 No. 5,325,889 for a laminated conduit plate for fluid delivery system
 (both issued to Millipore Corp.).
 Aspiration devices involve pneumatic forces or back pressure for its
 mechanism of action. See, e.g., U.S. Pat. No. 5,463,910 for a
 multi-function aspirating device (AVL Scientific Corp.); U.S. Pat. No.
 5,384,093 for an apparatus for aspirating and discharging a liquid sample
 (Toa Medical Electronics Co., Ltd.); and U.S. Pat. No. 5,525,302 for a
 method and device for simultaneously transferring plural samples.
 A multiwell plate is disclosed in PCT WO 97/15394 published May 1, 1997
 (SmithKline Beecham Corporation). The wells have a large opening at the
 top and small nozzle hole in the base. The opening is chosen so that a jet
 of liquid is emitted when a pressure pulse is applied to the surface such
 that by selecting a time for the pressure pulse a precise amount of volume
 in the well can be dispensed.
 SUMMARY OF THE INVENTION
 One aspect of the present invention is a device comprising a plate having a
 plurality of transfer elements. Each of the transfer elements comprises an
 aperture in the plate where the aperture is capable of being electrically
 activated. The plate has one or more attaching elements for attaching the
 plate to a multiwell plate to form a sealed system except for the
 apertures of the transfer elements. Usually, the device is adapted for
 sealing attachment to a multiwell plate.
 Another embodiment of the present invention is an apparatus for
 transferring liquid. The apparatus comprises a first plate comprising a
 plurality of individual wells containing the liquid. The wells rae formed
 in the first plate on a first side thereof wherein the second side of the
 plate is free of holes. The apparatus also comprises a second plate
 comprising a first side and a second side and a plurality of transfer
 elements comprising apertures in the second plate. Each of the apertures
 is capable of being electrically activated. The second plate is adapted
 for simultaneously transferring precise amounts of a liquid from the first
 plate to a sample receiving plate by electrically activating the
 apertures. The second side of the second plate is sealingly attached, and
 may be removably attached, to the first side of the first plate.
 Another aspect of the present invention is a method for transferring
 liquid. A quantity of liquid is disposed to a second side of a plate
 having a plurality of apertures in the plate. The apertures are capable of
 being electrically activated. The liquid is present in a closed well
 except for the apertures in the plate. To simultaneously expel liquid
 through the apertures, the apertures are electrically activated.
 Another aspect of the present invention is a method for transferring
 liquid. A first plate is used comprising a plurality of individual wells
 containing the liquid. The wells are formed in the first plate on a first
 side thereof. A second plate is also used. The second plate comprises a
 first side and a second side and a plurality of transfer elements, each
 comprising an aperture in the second plate. Each of the apertures is
 capable of being electrically activated. The second plate is adapted for
 simultaneously transferring precise amounts of a liquid from the first
 plate to a sample receiving plate by electrically activating the
 apertures. The second side of the second plate is sealingly attached, and
 may be removably attached, to the first side of the first plate. The
 apertures are positioned adjacent to an array of sample receiving
 reservoirs of a third plate, and the apertures are electrically activated.
 Another aspect of the present invention is a method for transferring
 liquids. A multiwell plate is provided having liquid contained in the
 wells thereof. A second plate is provided and comprises a first side and a
 second side and a plurality of apertures. Each of the apertures is at
 least partially comprised of an electroconductive material. The second
 plate is attached to the multiwell plate such that each of the apertures
 is aligned with a corresponding well of the multiwell plate. The second
 plate comprises, on-the second side, one or more attaching elements. The
 second plate is attached to the top of the multiwell plate by the
 attaching elements. The multiwell plate is attached to the second plate
 and the assembly is inverted so that liquid is disposed at each of the
 apertures. The dimensions and surface properties of the apertures are such
 that liquid does not exit the apertures under gravity conditions. The
 apertures are positioned adjacent to an array of sample receiving
 reservoirs of a microfluidic network in a third plate. Each of the
 microfluidic networks has an electrode connected to an electrode attached
 to the aperture. An electric potential is applied across the
 electroconductive material of the aperture and the opposing electrode
 establishing an electrostatic field that causes a portion of the liquid to
 exit the aperture as an electrospray and enter a corresponding sample
 receiving reservoir.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS
 This invention encompasses methods and apparatus for multiplexing fluid
 transfer from multiwell source plates to sample receiving plates such as a
 planar surface or a sample receiving reservoir of a miniaturized cassette,
 in which chemical syntheses and analyses are possible. The invention
 provides a fluid application device for dispensing sample droplets to an
 array of spots on a planar surface or an array of receiving reservoirs on
 a microfluidic-based cassette from an array of sample wells. The invention
 further provides a means for enabling fluid transfer between the disparate
 dimensions associated with the size of a-sample reservoir (milliliter to
 microliter range) in, for example, a 96 or 384 well plate, and the volume
 of sample or reagents, (nanoliter to picoliter range) in a microfluidic
 device. The ability to achieve fluid communication in an automated manner
 across this so-called "macro-to-micro" transition is particularly useful
 for high throughput screening (HTS) applications, including pharmaceutical
 drug discovery and genomic science applications.
 In one embodiment of the invention, sample handling is achieved by
 employing liquid-dispensing means housed within a protective cover
 assembly for the source plate. The cover assembly contains one transfer
 element for each well of the source or library plate, to which the
 assembly may be attached permanently or removably. The cover assembly
 device in its simplest concept is a cover plate comprising a plurality of
 nozzles that upon activation simultaneously dispense liquid droplets into
 the fluid--receiving sites of a microfluidic assay card. The mechanism of
 action of liquid transfer is electrical activation of the apertures.
 Accordingly, the transfer may be electrodynamically driver, including
 electrostatic spray or piezoelectric nozzles.
 The sample-transfer devices of the present invention serve as a
 fluid-communication means for dispensing liquids having a volume ranging
 from microliters to nanoliters and potentially as small as picoliters,
 starting from samples in the milliliter to microliter range. Demand for
 having the capability to bridge the macro-to-micro transition has arisen
 from the emergence of microfluidic devices for use in HTS applications.
 Advantages of the invention as distinguished from conventional HTS include
 the elimination of wash steps, dead volume, carry-over and the significant
 reduction of contamination, in addition to being compatible with existing
 laboratory ware. For example, the sample transfer devices and methods of
 the invention serve as a hybrid system and are particularly well suited to
 integrating standard 96 and 384 multi-well sample plates with microfluidic
 network systems and corresponding robotic-based instrumentation for
 ultra-high throughput sample processing and analyses. The device of the
 present invention may be used with standard multiwell plates thereby
 avoiding the need for specialized plates. No special design is necessary
 for the multiwell plate. As will be appreciated by the skilled artisan,
 the present invention is quite versatile.
 Before proceeding further with a detailed description of the present
 invention, a number of terms as used herein are defined.
 Multiwell plate--a plate comprising an array of wells. The plate may have
 any number of wells, which are usually in a pattern, and are usually
 plates having 96, 192, 384 or 1536 wells or larger. Exemplary of such well
 plates are microtiter plates having a pattern of wells. The wells extend
 into the substrate forming the plate. The wells are open at the top
 surface of the plate and closed at the bottom surface thereof. There are
 no openings, holes or other exits from the wells other than from the top
 surface at the opening of the well.
 Array--an arrangement of a plurality of elements such as a plurality of
 wells in a multiwell source plate, a plurality of apertures or nozzles in
 a sample transfer plate, a plurality of microfluidic networks on the
 multi-assay card, and so forth.
 Planar array--an array that is arranged in a plane, which may be the plane
 of an object such as, for example, a planar substrate, comprising the
 array.
 Microfluidic--of or pertaining to fluids and being of a magnitude on the
 order consistent with capillary dimension.
 Microfluidic processing--processing carried out on a microfluidic scale.
 The processing involves fluid handling, transport and manipulation within
 chambers and channels of capillary dimension. Valveless sample injection
 is achieved by moving fluid from the reagent reservoirs into cross-channel
 injection zones, where plugs of buffer or test compounds are precisely
 metered and dispensed into a desired flowpath. The rate and timing of
 movement of the fluids in the various microchannels can be controlled by
 electrokinetic, magnetic, pneumatic, and/or thermal-gradient driven
 transport, among others. These sample manipulation methods enable the
 profile and volume of the fluid plug to be controlled over a range of
 sizes with high reproducibility. In addition, microfluidic processing may
 include sample preparation and isolation where enrichment microchannels
 containing separation media are employed for target capture and
 purification. Microfluidic processing may also include reagent mixing,
 reaction/incubation, separations and sample detection and analyses.
 Microfluidic network--a system of interconnected cavity structures and
 capillary-size channels configured with a plurality of branches through
 which fluids may be manipulated and processed.
 Cavity structure--an unfilled space with a mass, preferably, a hollowed out
 space in an object, such as, e.g., a planar substrate, a plate, or the
 like in accordance with the present invention such as, for example, a
 well, a reservoir, a chamber for incubation or separation or detection,
 and the like.
 The cavity structures are usually present at one or both of the termini,
 i.e., either end, of a channel. The cavity structures may serve a variety
 of purposes, such as, for example, means for introducing a buffer
 solution, elution solvent, reagent rinse and wash solutions, and so forth
 into a main channel or one or more interconnected auxiliary channels,
 receiving waste fluid from the main channel, and the like.
 Channels--a conduit or means of communication, usually fluid communication,
 more particularly, liquid communication, between elements of the present
 apparatus. The elements in communication are, e.g., cavity structures, and
 the like. Channels include capillaries, grooves, trenches, microflumes,
 and so forth. The channels may be straight, curved, serpentine,
 labyrinth-like or other convenient configuration within the planar
 substrate. The cross-sectional shape of the channel may be circular,
 ellipsoidal, trapezoidal, square, rectangular, triangular and the like so
 that it forms a microchannel within the planar substrate in which it is
 present.
 The inside of the channel may be coated with a material for strength, for
 modifying, enhancing or reducing electroosmotic flow, for enhancing or
 reducing electrophoretic flow, for modification of surface
 hydrophobicity/hydrophilicity, for binding of selected compounds, and so
 forth. Exemplary of coatings are silylation, polyacrylamide (vinyl-bound),
 methylcellulose, polyether, polyvinylpyrrolidone, and polyethylene glycol,
 polypropylene, Teflon.TM. (DuPont), Nafion.TM. (DuPont), polystyrene
 sulfonate and the like may also be used. See also U.S. patent application
 Ser. No. 08/715,338, the relevant disclosure of which is incorporated
 herein by reference.
 Capillary dimension--a cross-sectional area that provides for capillary
 flow through a channel. At least one of the cross-sectional dimensions,
 e.g., width, height, diameter, is at least about 1 .mu.m, usually at least
 10 .mu.m, and is usually no more than 500 .mu.m, preferably no more than
 200 .mu.m. Channels of capillary dimension typically have an inside bore
 diameter (ID) of from about 10 to 200 microns, more typically from about
 25 to 100 microns.
 Electroflow--the manipulation of entities such as molecules, particles,
 cells, vitreous fluid and the like through a medium under the influence of
 an applied electric field by use of electrodes and the like to induce
 movement such as electrokinetic flow, electroosmotic flow, electrophoretic
 flow, dielectrophoretic flow, and so forth. Depending on the nature of the
 entities, e.g., whether or not they carry an electrical charge, as well as
 the surface chemistry of the chamber in which the electroflow is
 conducted, the entities may be moved through the medium under the direct
 influence of the applied electric field or as a result of bulk fluid flow
 through the pathway resulting from the application of the electric field,
 e.g., electroosmotic flow. It is within the purview of the present
 invention that electroflow can be carried out in conjunction with movement
 of material by gravity or by application of a magnetic field, centrifugal
 force, thermal gradients, aspiration, negative pressure, pumping,
 pneumatic forces, and the like.
 Electroflow medium--an electrically conductive medium; a medium generally
 utilized in carrying out microfluidic processes. The particular medium
 chosen is one that is suitable to a particular application of the present
 invention. Such media include, for example, buffer solutions, cross-linked
 and uncross-linked polymeric solutions, organic solvents, detergents,
 surfactant micellular dispersions, gels of the type generally used in
 connection with analytical separation techniques and other microfluidic
 processes, and so forth. For example, cross-linked polyacyrlamide gel,
 cellulose derivatives, uncross-linked polyacrylamide and derivatives
 thereof, polyvinyl alcohols, polyethylene oxides and the like may be used.
 For a discussion of such media see, e.g., Barron and Blanch, "DNA
 Separations by Slab Gel and Capillary Electrophoresis: Theory and
 Practice," Separation and Purification Methods (1995) 24:1-118.
 The electroflow medium may be a conventional buffer such as, for example,
 the Good'buffers (HEPES, MOPS, MES, Tricine, etc.), and other organic
 buffers (Tris, acetate, citrate, and formate), including standard
 inorganic compounds (phosphate, borate, etc.). Exemplary buffer systems
 include: i) 100 mM sodium phosphate, pH 7.2; ii) 89.5 mM tris-base, 89:5
 mM Boric acid, 2 mM ETDA, pH 8.3. Buffer additives include: methanol,
 metal ions, urea, surfactants, and zwitterions, intercalating dyes and
 other labeling reagents. Polymers can be added to create a sieving buffer
 for the differential separation of nucleic acids based on fragment length.
 Examples of such polymers are: polyacrylamide (cross-linked or linear),
 agarose, methylcellulose and derivatives, dextrans, and polyethylene
 glycol. Inert polymers can be added to the separation buffer to stabilize
 the separation matrix against factors such as convective mixing.
 Alternatively, buffers containing micelles could be used for effecting
 separation of electrically neutral or hydrophobic substances of interest.
 The micelles are formed in the buffer by addition of an appropriate
 surfactant at a concentration exceeding the critical micelle concentration
 of that detergent. Useful surfactants include but are not limited to
 sodium dodecyl sulfate, dodecyltrimethyl ammonium bromide, etc. Weakly
 charged or apolar analytes partition into the micelles to different
 degrees depending upon their degree of hydrophobicity and thus can be
 separated. This subtechnique of capillary electrophoresis is termed
 micellar electrokinetic chromatography.
 Electrophoresis--separation of components in a liquid by electroflow.
 Various forms of electrophoresis include, by way of example and not
 limitation, free zone electrophoresis, gel electrophoresis,
 isotachophoresis, high performance CE, capillary zone electrophoresis, and
 the like.
 Electrophoresis column--in the context of the present invention, a channel
 for carrying out electrophoresis.
 Electroforming--involves the electrodepositing of metal onto or into a mold
 or mandrel to produce a free standing metal object. The master pattern may
 be made from an original design or an actual article. The
 electrodeposition can be carried out to produce specified characteristics
 in the plated deposit. Various electroforming techniques are well-known in
 the art and will not be repeated here.
 Electrical activation (electrically activated)--activation that is
 electrodynamically driven, including electrostatic activation,
 piezoelectric activation, and the like. Electrostatic activation is
 typically implemented by generating a 1.0 to 1.5 kV potential between a
 fluid reservoir with a nozzle or tip of target surface. Applied pulses of
 0.5 to 1.0 kV can propel micron-sized droplets of picoliter volumes, or
 create continuous microstreams of 10 to 100 ml/hour. In the case of
 typical piezoelectric activation, picoliter to nanoliter droplets can be
 delivered at 1 kHz frequencies by cycling the deformation of a
 piezoelectric material via voltage modulation. Recent advances in
 high-frequency printing mechanisms have made it possible to deliver such
 droplets at 50 kHz frequencies by using a piezoelectric element to vibrate
 a microfabricated cantilevered beam with a tip that is in fluid
 communication with a liquid reservoir. For a further description of
 piezoelectric activation, see U.S. Pat. No. 5,164,740, the relevant
 disclosure of which is incorporated herein by reference.
 Electroconductive material--material that is capable of transporting an
 electrical stimulus. Exemplary of such material are metals such as, e.g.,
 nickel, copper, gold, silver, platinum, rhodium, palladium, and the like
 and alloys thereof such as, e.g., gold-copper alloy, palladium-nickel
 alloy, stainless steel, and so forth.
 Planar surface--a planar surface is any generally two-dimensional structure
 on a solid substrate, which is usually rigid. The surface may be composed
 of any of a wide variety of materials, for example, polymers, plastics,
 resins, polysaccharides, silica or silica-based materials, carbon, metals,
 inorganic glasses, membranes, etc. The surface may be non-reactive to the
 liquid deposited thereon or it may contain reactive functionalities for
 binding to a component of the liquid. On the other hand, the surface may
 contain one or more reagents for conducting a chemical synthesis or
 analysis. The substrate upon which the surface lies may be composed of the
 same material as the surface. The substrate may have any convenient shape
 such as disk, square, and the like. Where the substrate is formed from a
 different material than the surface, the substrate may be formed from
 glass, modified silicon, polymeric material, such as
 polytetrafluoroethylene, polyvinylidenedifluoride or combinations thereof.
 Other substrate materials will be readily apparent to those of skill in
 the art upon review of this disclosure.
 As mentioned above, one aspect of the present invention is a device
 comprising a plate having an array of transfer elements. The transfer
 elements comprise an array of apertures in the plate wherein each of the
 apertures is capable of being electrically activated. This is usually
 achieved by having at least a portion of the aperture comprise an
 electroconductive material. The configuration of the transfer elements
 generally conforms to the spacing format of the wells of a multiwell
 plate. The dimensions of the apertures are usually about 0.001 to 0.020
 inches in diameter, preferably, about 0.005 to 0.01 inches in diameter.
 Optionally, the area adjacent apertures in a plate may form a protrusion in
 the plate. Each protrusion corresponds to an aperture in the plate and
 extends the surface of the plate out of the plane of the plate. The
 protrusions from each of the apertures is generally tubular and of
 capillary dimensions.
 It should be understood that the number of transfer elements associated
 with the plate may be less than the number of wells in a multiwell plate.
 For example, for a 96 well plate, the number of transfer elements in the
 transfer element plate may correspond to only one row of wells in the 96
 well plate, i.e., 8 transfer elements in a single row. Several different
 transfer element plates may be employed independently of one another for
 the 96 well plate. Each of the transfer element plates may have a single
 row of 8 transfer elements where the single row in each corresponds to a
 different 8-well row of the 96 well plate. Other variations will be
 evident to those skilled in the art in view of the above disclosure. Thus,
 simultaneous transfer of liquids may be achieved for less than all of the
 wells in a multiwell plate.
 The inner surface of the apertures and protrusions may be coated with a
 material that is conductive, preferably of higher conductivity than the
 liquid to be transferred and may be hydrophilic. In this regard the
 aperture, and/or the protrusion, may be formed from, or the inner surface
 thereof coated with, an electroconductive material. The apertures and/or
 protrusions may be coated with the electroconductive material by
 electroforming, sputtering, vacuum deposition, chemical deposition,
 electroplating, conductive inks, insert molding of conductive material
 such as stainless steel, and so forth. The transfer elements are designed
 to retain a quantity of liquid under normal conditions of gravity,
 vibration, handling, capillary action and the like. In other words the
 liquid does not exit the transfer elements until application of an
 external force. This feature is usually achieved by the design of the
 transfer elements. The apertures themselves, or the protrusions, may have
 any convenient shape such as, for example, circular, rectangular, oval,
 tubular, funnel-shaped, conical (varying diameter) or varying
 cross-sections such as truncated pyramid, and so forth. The protrusions
 can be tapered or straight. The protrusion is usually shaped in the form
 of a nozzle. The length of the protrusions is about 0.005 to 0.5 inches,
 preferably, about 0.05 to 0.10 inches, more preferably, about 0.050
 inches. Usually, the length of the protrusions is related to the inner
 dimensions of the protrusion. Again, the overall consideration is that the
 liquid not exit the transfer elements until application of some force.
 The exit orifice of the aperture or protrusion has an effect on the quality
 of the dispensation of the liquid from the transfer elements. In general,
 the smaller the diameter of the exit orifice, the smaller the volume of
 the drop of liquid ejected through the transfer elements. The dimensions
 of the exit orifice also have a large influence on the linear velocity of
 the dispensed liquid. The linear velocity must not be so great as to cause
 excessive splashing. In general, the exit orifice has dimensions of about
 0.001 to 0.020 inches, preferably, about 0.003 to 0.010 inches, more
 preferably, about 0.005 inches.
 The physical properties of the liquids to be dispensed also play a role in
 the composition, dimensions and geometry of the transfer elements. The
 composition of the transfer elements must be compatible with the liquid.
 Where the liquid contains particulate material, the dimensions of
 particularly the exit orifice must be such as to avoid clogging of the
 transfer element. Also of consideration are the viscosity, surface tension
 and density of the liquid to be transferred. As the viscosity of a liquid
 increases, the minimum dispensable volume achievable generally also
 increases. Surface tension has most impact on formation of droplets and
 the ability of the liquid to adhere to the protrusion. In general, as
 surface tension increases, the ability to dispense reliably also
 increases. Density has primary influence on the kinetic energy of the
 droplet. Generally, the greater the density, the greater the kinetic
 energy of the droplet. For the most part the particular parameters for the
 transfer elements may be determined empirically taking into consideration
 the above comments.
 As will be appreciated, the volume of the liquid that enters the aperture
 and that is transferred from the multiwell plate to a sample receiving
 plate is determined, among others, by the dimensions of the apertures and
 the surface tension properties of the liquid and the surrounding area of
 the aperture and of the microwell plate. The liquid to be transferred is
 disposed adjacent to the apertures. In this regard the liquid may fill all
 or only a portion of the apertures. Furthermore, the liquid may simply
 form a meniscus at the opening of the aperture where the meniscus is
 convex at the opening of the aperture at which it is disposed and, thus,
 extends partially into the aperture. When liquid enters the aperture
 and/or protrusion, the volume of liquid that is usually about 0.1
 nanoliter to about 2.5 microliters. The dimensions of interest for the
 apertures are primarily the inner dimension and the length. Retention of a
 certain volume of sample in the apertures is also dependent on the nature
 of the inner surface of the apertures. Accordingly, the inner surface of
 the apertures, and/or the protrusions, may be made hydrophobic or
 hydrophilic as desired.
 The device is generally adapted for sealing attachment, optionally,
 removable attachment, to a multiwell plate. Removable attachment may be
 achieved by utilizing one or more attaching members, each corresponding to
 a well of a muiltiwell plate. The attaching members may also serve as
 positioning elements by assuring the alignment of the transfer elements
 with the wells of the multiwell plate when the present device is attached
 to the multiwell plate. The attaching element not only serves to secure
 the device to the multiwell plate, it may also provide for a sealing
 attachment. It is important that a proper seal be formed when the device
 is attached to the multiwell plate. When the plate is manipulated such as
 by inverting the plate to position the transfer elements, the liquid in
 the wells must not exit the wells except from the transfer elements and
 only upon activation. The attaching elements may be friction members,
 adhesive layer, press fit, and the like.
 The friction members may be constructed from elastomeric material such as
 rubber including soft rubber, which may be natural or synthetic, including
 styrene-butadiene rubber; neoprene and nitrile rubbers; butyl,
 epichlorohydrine, ethylene-propylene rubbers; polyurethane rubbers;
 silicone and fluorosilicone rubbers; fluorocarbon rubbers; and so forth,
 as well as some other suitable material such as, e.g., low hardness
 thermoplastic materials, such as polyether- and polyester-based
 polyurethanes, polyvinyl chloride and fluoroelastomers. Alternatively,
 removable attachment may be achieved using materials such as ceramics,
 plastics, rubbers, and the like coated with a material that imparts
 slidability such as Teflon and the like.
 One of the particularly advantageous features of the present invention is
 that the device and the microwell plate may be reused after washing. Thus,
 for this embodiment the device is attached to the multiwell plate, samples
 are transferred to a sample receiving plate in accordance with the present
 invention, the device is detached from the multiwell plate and the device
 and the microwell plate are washed for reuse. However, another advantage
 of the invention is that the device may be disposed of conveniently while
 the multiwell plate may be washed and reused.
 In another aspect the apparatus comprising a microwell plate with the
 attached device in accordance with the present invention may be used to
 transfer liquids to a sample receiving plate. Thereafter, the apparatus
 may be stored for a period of time and then another aliquot of liquid
 transferred. This process can be repeated a number of times depending on
 the volume of liquid available in wells of the microwell plate. In this
 approach it is convenient to have a cover for the device of the present
 invention. This cover can be removably attached to the device opposite to
 the attached microwell plate. In this way the contents of the microwell
 plate may be incubated or the apparatus simply stored in a cold room until
 another transfer is desired. Such a cover may be conveniently made of
 plastic or other suitable material and is generally of a size
 corresponding to the size of the device. The cover may have sides that
 slip over at least a portion of the sides of the apparatus.
 There may be one or several attaching elements per transfer element
 depending on the design of the attaching elements. For example, the
 attaching element may be a circumferential lip extending from a side of a
 plate opposite the side from which the protrusions extend. Alternatively,
 the attaching element may comprise several fingers depending from such
 side of the plate. Thus, the friction members may be in the form of a
 gasket, finger elements, preformed film and so forth. The friction member
 may be secured to the transfer element plate by physical adherence or
 permanent bonding using standard adhesive technology.
 In another approach the attaching element providing for sealing attachment
 may be a non-permanent removable adhesive layer. The adhesive must be
 capable of providing a liquid tight seal with the top surface of the
 multiwell plate and must not be reactive with, or detrimental to, any
 component of the liquid in the wells of the multiwell plate. Suitable
 adhesives for forming an adhesive layer that provides for removing
 attachment include adhesives that are generally flexible, tacky, low
 cross-link density, pressure sensitive, and the like. Such adhesives
 include, for example, acrylic based, e.g., methacrylates, cyanoacrylates,
 etc., elastomeric, e.g., Neoprene, nitriles, polyurethanes, silicones,
 polysulfides, etc., plasticized hot melt, e.g., polyamides, polyesters,
 polyethylenes, polysulfones, vinyl acetates, etc. and the like. On the
 other hand the adhesive may be permanent and non-removable such as, for
 example, acrylic-based, epoxies, hot melt, elastomeric and so forth
 including some of the above where increased permanency is obtained by
 selecting for less flexibility and providing longer curing times.
 It is also within the purview of the present invention that the adhesive
 layer be an adhesive coated on a support plate that is secured to the
 transfer element plate. The support plate may be a generally planar
 substrate fabricated from one or more of the materials mentioned above
 with respect to the friction members. Other examples of ways in which
 sealing attachment of the device to a multiwell plate may be realized
 include thermal bonding, clamping mechanisms, and so forth.
 When the device of the present invention is attached to the top of a
 multiwell plate by means of the attaching elements, a sealed system is
 formed except for the apertures in the present device. Thus, attachment of
 the present device to a multiwell plate produces a closed chamber with the
 only exit port being that provided by a transfer element in accordance
 with the present invention.
 The present device may be fabricated as a unitary plate or it may be
 constructed from several parts assembled into the device. For example, the
 plate may be made from plastic, plastic coated with an electroconductive
 material, an electroconductive material alone, and the like. The array of
 apertures may be made in the plate by laser cutting, etching, piercing,
 drilling, punching, direct molding or casting from a master with pins, and
 so forth.
 Where the transfer element includes a protrusion, the protrusions are
 formed in the plate by means of electrical plating, electroforming,
 stamping and the like. The protrusions may be separately attached to the
 plate adjacent to the apertures. In the latter situation the protrusions
 may be of an electroconductive material and are preformed in the desired
 shape, e.g., nozzle, tapered nozzle, conical nozzle and so Separately
 formed protrusions may be attached to one side of the plate by suitable
 bonding means such as, e.g., adhesives, press fits, and so forth.
 The other side of the plate has one or more attaching elements for
 attaching the plate to a plate comprising a plurality of sample containers
 such as a multiwell plate. If the attaching element is an adhesive layer,
 tacky material, or the like, the side of the plate bearing the adhesive
 layer or tacky material is covered with a suitable removable backing such
 as, for example, non-sticking plastic sheets, wax paper, and the like. The
 plate usually is about the same size as the multiwell plate to which it is
 attached. Typically, a standard 96 well plate is about 3.4 inches in
 width, about 5.0 inches in length, and about 0.6 inches in thickness. The
 thickness of the plate generally depends on the particular construction of
 the plate. It should be obvious that the dimensions of the plate are not
 critical as long as the dimensions are compatible with the microwell
 plate.
 For applications where it is desired to have a disposable device, due to
 ease of manufacture and cost of materials, at least part of the device
 typically is fabricated from a plastic. Particular plastics finding use
 include polypropylene, such as high density polypropylene,
 polymethylmethacrylate, polycarbonate, polyethylene terephthlate,
 polystyrene or styrene copolymers, and the like. Of course, at least part
 of the aperture, or any protrusion, should be fabricated from, or coated
 with, an electroconductive material.
 The device may be fabricated using any convenient means, including
 conventional molding and casting techniques. For example, a planar or flat
 plastic plate is injection molded with an array of countersunk apertures
 in a pattern corresponding to that of the wells in a microwell plate. In
 one approach an electroconductive material is electroformed on part or all
 of the inner surface of the aperture. Metal nozzles may be electroformed
 to the underside of the aperture locations.
 In addition, production techniques used in flexible circuitry fabrication
 can be employed. Such fabrication techniques include conductive ink
 printing, imaging and etching or mechanically cutting metal foils, or
 forming and placing wire by numerical control (NC) equipment. The
 dielectric layers are tightly bonded to the conductive pattern using
 lamination techniques.
 In one embodiment, once the apertures have been formed in the plate, an
 adhesive layer is applied to one side. The adhesive layer has
 through-holes having essentially the same centers as the apertures in the
 plate. However, the diameter of the through-holes of the adhesive layer
 are larger than that of the apertures and usually will approximate the
 diameter of the sample containers such as the wells of a multiwell plate.
 The adhesive layer is usually about 0.01 to 0.5 mm in thickness. The
 through-holes in the adhesive may be formed by molding, laser cutting, and
 so forth. The adhesive layer has a removable backing that is placed over
 the entire area of the adhesive layer.
 For attaching elements that are friction members, a single substrate sheet
 may be employed with the friction members formed thereon in an array
 corresponding to the wells of the multiwell plate.
 An example of one device in accordance with the present invention is
 depicted in FIGS. 1-2. Device 100 comprises a plate 20 having an array of
 transfer elements 22. The transfer elements each comprise a aperture 30 in
 plate 20. Plate 20 has outer lip 21 extending upward from plate 20 and
 extending around the perimeter of plate 20. Above plate 20 is adhesive
 layer 38 and removable backing 26. Backing 26 is shown as a transparent
 material in FIG. 1; however, backing 26 may be translucent or opaque. An
 array of through-holes 37 are present in adhesive layer 38 generally
 corresponding in location and centered with respect to the array of
 apertures 30. Through-holes 37 usually have a diameter that is about the
 diameter of the top of the wells in a standard multiwell plate, usually,
 about 4 mm. It is evident that the diameter of the through-holes can be
 larger of smaller depending on the diameter of the wells in a non-standard
 multiwell plate.
 An alternate embodiment of the present invention is shown in FIG. 2B
 wherein apertures 30 have a funnel shape resulting from a circumferential
 bevel 36. Bevel 36 results from circumferential tapering from the side
 wall 28 adjacent to aperture 30 to the top rim of aperture 30. Bevel 36 is
 at an angle of about 10 degrees to 45 degrees with respect to wall 28 of
 plate 20. The function of bevel 36 is to assist liquid into aperture 30
 when the present device is utilized.
 Another embodiment of the present invention is shown in FIG. 2C wherein
 transfer elements 22 comprise apertures 30 in plate 20, which has
 protrusion 32 adjacent each of apertures 30. Protrusion 32 forms a nozzle,
 thereby extending aperture 30 accordingly. Plate 20 also has
 circumferential bevel 39 adjacent the top of aperture 30. Bevel 39
 generally corresponds to protrusion 32. Bevel 39 results from
 circumferential tapering from the side wall 28 adjacent to aperture 30 to
 the rim of aperture 30. Bevel 39 is at an angle of about 10 degrees to 45
 degrees with respect to wall 28 of plate 20. The function of bevel 39 is
 to assist liquid into aperture 30 when the present device is utilized.
 An apparatus 50 in accordance with the present invention is depicted in
 FIGS. 3-4. Backing 26 is removed from plate 20, which is then attached to
 the top 52 of multiwell plate 54 having an array of wells 56 containing
 liquid 58. Plate 20 is pressed firmly into place on the top of multiwell
 plate 54 so that outer lip 21 fits snugly into cut out area 51, which
 extends around the periphery of plate 54. Adhesive layer 38 is pressed
 firmly against the front side 52 of multiwell plate 54. The construction
 of plate 20 is such that each of the transfer elements 22 are aligned with
 a corresponding well 56 of multiwell plate 54. In general the apertures
 are aligned so that the apertures are substantially centered with respect
 to the top of wells 56.
 Once device 100 is attached to multiwell plate 54, the resulting apparatus
 50 is inverted so that each of the apertures 30 fills with liquid. A
 meniscus 60 is formed at opening 34. Apparatus 50 is, for example, then
 positioned adjacent to an array of sample receiving reservoirs 142, which
 are part of microfluidic networks 108 in a microfluidic network plate 110
 as depicted in FIG. 5. Each of the microfluidic networks 108 has an
 electrode 64 connected to an electrode 62 attached to transfer element 22.
 An electric potential is applied to the electroconductive material means
 of electrodes 62 and 64 causing a precise amount of liquid 58 in each of
 transfer elements 22 to be forced out of the transfer elements and into a
 corresponding sample receiving reservoir 142.
 FIG. 4B shows the positioning of electrode 62 in the embodiment of FIG. 4A.
 Electrode 62 is shown adjacent aperture 30 of plate 20. In this depiction
 the electrode appears similar to a through-hole in a printed circuit board
 trace. The electrodes employed may be selected from those electrodes that
 are described more fully below with respect to the microfluidic networks.
 The apparatus is disposed relative to the microfluidic network plate so
 that the transfer elements are aligned with the sample receiving
 reservoirs. As the number of samples in the array increases, alignment
 becomes more critical. A positioning device may be used to provide for
 precise alignment. Such device may be part of an instrument into which the
 present apparatus and the microfluidic network plate are inserted for
 activating the electroconductive material and for driving the electroflow
 in the microfluidic network plate. Positioning will generally be
 accomplished by mechanical, electromechanical, manual or similar means as
 is known in the art.
 Alignment may also be affected by the forces acting on the droplet in
 flight from the exit orifice of the protrusion to the sample receiving
 reservoir. Air currents can alter the trajectory of the droplet. In
 addition, electrostatic charge differences between the droplet and the
 sample receiving plate can affect the path of the droplet. Consideration
 must be made of the above and the apparatus handled accordingly.
 Microfluidic network plate 310 comprises an array of microfluidic networks
 308 having interconnected cavity structures 342 and 346 and channels 320
 (see FIG. 7). Each of the microfluidic networks corresponds to a
 respective sample transfer element 22 of device 100. The microfluidic
 network has interconnected cavity structures and channels, the latter
 forming one or more flowpaths resulting in an interconnected system. In
 general, there is a main flowpath and one or more secondary flowpaths. A
 desired microfluidic process may be carried out in the main flowpath or in
 one of the secondary flowpaths. The additional flowpaths may be employed
 for a variety of purposes such as, for example, enrichment of a sample,
 isolation, purification, dilution, and the like. A variety of
 configurations are possible, such as a branched configuration in which a
 plurality of flowpaths are in fluid communication with the main flowpath.
 See, for example, U.S. Pat. No. 5,126,022.
 The main flowpath has associated with it at least one pair of electrodes
 for applying an electric field to the medium present in the flowpath.
 Where a single pair of electrodes is employed, typically one member of the
 pair is present at each end of the pathway. Where convenient, a plurality
 of electrodes may be associated with the flowpath, as described in U.S.
 Pat. No. 5,126,022, the relevant disclosure of which is herein
 incorporated by reference, where the plurality of electrodes can provide
 for precise movement of entities along the flowpath. The electrodes
 employed may be any convenient type capable of applying an appropriate
 electric field to the medium present in the flowpath with which they are
 associated.
 An example of a basic configuration of a microfluidic network is shown in
 FIG. 5. Plate 110 is comprised of a plurality of microfluidic networks
 108. Each network comprises main flowpath 120 and secondary flowpath 122,
 which intersect at 124. Electrode 130 is connected to reservoir 132 and
 electrode 134 is connected to reservoir 136. An electric potential can be
 applied to flowpath 122 by means of electrodes 130 and 134. Electrode 140
 is connected to sample introduction port and reservoir 142 and electrode
 144 is connected to reservoir 146. An electric potential can be applied to
 main flowpath 120 by means of electrodes 140 and 144. The main flowpath
 120 has optional portion 150 that is tortuous to provide an appropriate
 path length and residence time to achieve mixing by diffusion, incubation,
 and so forth.
 Secondary flowpath 122 has detection zone 148 where the result of a
 microfluidic process may be detected. For example, if the microfluidic
 process is an assay for an analyte, the detection zone permits the
 detection of a signal produced during the assay. Alternatively, if the
 microfluidic process is a chemical synthesis, the detection zone may be
 used to detect the presence of the synthesized compound. It is, of course,
 within the purview of the present invention to utilize several detection
 zones depending on the nature of the microfluidic process. There may be
 any number of detection zones associated with a single channel or with
 multiple channels. Suitable detectors for use in the detection zones
 include, by way of example, photomultiplier tubes, photodiodes, photodiode
 arrays, avalanche photodiodes, linear and array charge coupled device
 (CCD) chips, CCD camera modules, spectrophotometers, spectrofluorometers,
 and the like. Excitation sources include, for example, filtered lamps,
 LED'S, laser diodes, gas, liquid and solid state lasers, and so forth. The
 detection may be laser scanned excitation, CCD camera detection, coaxial
 fiber optics, confocal back or forward fluorescence detection in single or
 array configurations, and the like.
 Detection may be by any of the known methods associated with the analysis
 of capillary electrophoresis columns including the methods shown in U.S.
 Pat. No. 5,560,811 (column 11, lines 19-30), U.S. Pat. Nos. 4,675,300,
 4,274,240 and 5,324,401, the relevant disclosures of which are
 incorporated herein by reference. An example of an optical system for
 reading the channels in the detection zones comprises: a power supply,
 which energizes a photomultiplier tube. A power supply energizes a 75 watt
 Xenon lamp. Light from the lamp is condensed by focusing lens, which
 passes light to an excitation filter. A dichroic mirror directs excitation
 light to a microscope. The apparatus is mounted on a so that light passes
 over the channels. Fluorescent emission light is collected by the
 microscope, passed through a dichroic mirror, emission filter, spatial
 filter before reaching the photomultiplier (PMT). The output signal of PMT
 is fed to an analog-to-digital converter, which in turn is connected to
 computer.
 Alternatively, a static detection system in which a stationary detection
 point some distance from the injection end of the capillary is monitored
 as bands to be analyzed traverse the length of the capillary and pass by
 the detection zone could be used. This type of detection could be
 implemented using optical fibers and lenses to deliver the excitation
 radiation to the capillary and to collect the fluorescent emission
 radiation from the detection zone in the capillary. Appropriate
 multiplexing and demultiplexing protocols might be used to sequentially
 irradiate and monitor a large array of capillaries using a single source
 and a single or a small number of photodetectors. Using this approach,
 each capillary in the array is sequentially polled to detect any analyte
 band in the detection zone of that capillary.
 The detectors may be part of an instrument into which the present apparatus
 and the plates containing the microfluidic networks is inserted. The
 instrument may be the same instrument that comprises the electrode leads
 and other components necessary for utilizing the present apparatus.
 However, separate instruments may be used for housing a sample container
 plate, incubation of sample and reagents, detection of a result,
 electrical field application, and other operations such as temperature and
 humidity control, and so forth. Humidity control may be achieved in a
 number of ways such as, for example, the use of humidistats, water vapor
 sources confined in the device in fluid communication with other areas
 thereof, and so forth. Other methods of humidity control will be evident
 to those skilled in the art.
 Generally, prior to using a microfluidic network a suitable electroflow
 medium as described above is introduced into the flowpaths defined by the
 channels in the secondary plate. The medium may be conveniently introduced
 through one of the reservoirs at the termini of each of the channels or
 directly into the channels themselves prior to sealing of a cover plate to
 the planar substrate.
 The use of a microfluidic network is next discussed with reference to FIG.
 5. Sample is introduced into sample introduction port and reservoir 142
 together with appropriate reagents for carrying out a microfluidic
 process. An electric potential is applied across electrodes 140 and 144
 causing medium containing the sample and other reagents to move through
 flowpath 120 and, in particular, portion 150 of 120. Mixing of sample and
 reagents, as well as incubation, take place in portion 150. When the
 portion of the medium containing the sample and reagents reaches
 intersection 124, the electric potential applied between electrodes 140
 and 144 is discontinued and an electric potential is applied between
 electrodes 130 and 134. The point at which the sample and other reagents
 reach intersection 124 may be determined by detecting the presence of the
 sample or one of the reagents directly or by empirically determining the
 time at which the sample and reagents should reach the intersection 124,
 based on the particular nature of the sample, the medium employed, the
 strength of the electric potential and so forth. Application of the
 electrical potential to electrodes 130 and 134 causes a plug of medium of
 precise amount (determined by the dimensions of the channel) to move along
 secondary flowpath 122 towards reservoir 136 and through detection zone
 148 where detection is conducted. This is the basic manner in which an
 exemplary microfluidic network operates. Of course, as will be appreciated
 by one of ordinary skill in the art, the precise manner of operation of
 microfluidic networks in an apparatus in accordance with the present
 invention is dependent on the construction of the apparatus.
 Considerations include, for example, whether reagents are present on board
 the apparatus or added from a source outside the apparatus. Other
 considerations include manipulation of beads or magnetic beads in the
 channels, filling of channels with buffer, manipulation of discrete drops
 within otherwise unfilled channels, method of fluid movement
 (electroosmotic, electrokinetic, surface tension, centrifugal, pneumatic),
 mixing two or more reagents, incubation, and so forth.
 Those skilled in the electrophoresis arts will recognize a wide range of
 electric potentials or field strengths may be used, for example, fields of
 10 to 1000 V/cm are used with 200-600 V/cm being more typical. The upper
 voltage limit for commercial systems is 30 kV, with a capillary length of
 40-60 cm, giving a maximum field of about 600 V/cm. There are reports of
 very high held strengths (2500-5000 V/cm) with short, small bore (10
 microns) capillaries micro-machined into an insulating substrate. Normal
 polarity is to have the injection end of the capillary at a positive
 potential. The electroosmotic flow is normally toward the cathode. Hence,
 with normal polarity all positive ions and many negative ions will run
 away from the injection end. Generally, the "end-of-capillary" detector
 will be near the cathode. The polarity may be reversed for strongly
 negative ions so that they run against the electroosmotic flow. For DNA,
 typically the capillary is coated to reduce electroosmotic flow, and the
 injection end of the capillary is maintained at a negative potential.
 Examples of plates that are suitable for the microfluidic network plate
 apparatus are provided in FIGS. 6-8. Only a portion of the microfluidic
 network plates is shown in FIGS. 6-8. It is to be understood that the
 microfluidic network plates may have any number of separate networks
 including more than or less than 96. The number of microfluidic networks
 may be multiples of 96 where the number is greater than 96 or multiples of
 8 where the number is less than 96. In addition, some of the features of
 the microfluidic networks are not shown in all of the networks depicted in
 FIG. 6-8.
 In FIG. 6 a portion of a plate 210 is shown where the entire plate may have
 up to ninety six (96) microfluidic networks 208. Each network comprises
 main flowpath 220 and secondary flowpath 222, which intersect at 224.
 Electrode 230 is connected to reservoir 232 and electrode 234 is connected
 to reservoir 236. An electric potential can be applied to secondary
 flowpath 222 by means of electrodes 230 and 234. Electrode 240 is
 connected to sample introduction port and reservoir 242 and electrode 244
 is connected to reservoir 246. An electric potential can be applied to
 main flowpath 220 by means of electrodes 240 and 244. The main flowpath
 220 has a portion 250 that is in the form of a linear reciprocating coil
 to provide a tortuous path.
 In FIG. 7 a portion of a plate 310 is shown where the entire plate may have
 up to ninety six (96) microfluidic networks 308. Each network comprises
 main flowpath 320 and secondary flowpath 322, which intersect at 324.
 Electrode 330 is connected to reservoir 332 and electrode 334 is connected
 to reservoir 336. An electric potential can be applied to secondary
 flowpath 322 by means of electrodes 330 and 334. Electrode 340 is
 connected to sample introduction port and reservoir 342 and electrode 344
 is connected to reservoir 346. An electric potential can be applied to
 main flowpath 320 by means of electrodes 340 and 344. The main flowpath
 320 is a circular coil to provide a tortuous path.
 In FIG. 8 a portion of a plate 410 where the entire plate may have up to
 ninety six (96) microfluidic networks 408. Each network comprises main
 flowpath 420 and secondary flowpath 422, which intersect at 424. Electrode
 430 is connected to reservoir 432 and electrode 434 is connected to
 reservoir 436. An electric potential can be applied to secondary flowpath
 422 by means of electrodes 430 and 434. Electrode 440 is connected to
 sample introduction port and reservoir 442 and electrode 444 is connected
 to reservoir 446. An electric potential can be applied to main flowpath
 420 by means of electrodes 440 and 444. The main flowpath 420 has a
 portion 450 that is in the form of a linear reciprocating coil to provide
 a tortuous path. The microfluidic networks of plate of FIG. 8 also
 comprise set of reagent reservoirs 452, 454, 456 and 458. Each of the
 reagent reservoirs has a channel providing communication between the
 reagent reservoir and each of the main flowpaths of the microfluidic
 networks. Accordingly, reagent reservoir 452 has a channel 470 that
 intersects main flowpath 420 at 460 for each of the microfluidic networks
 in row 462 of plate 410. Likewise, reagent reservoir 454 has a channel 472
 that intersects main flowpath 420 at 464 for each of the microfluidic
 networks in row 464 of plate 410. The same situation exists for reagent
 reservoirs 456 and 458. Reagents are moved through channels 470 and 472 by
 means of application of electric potential at electrodes 480 and 482,
 respectively. By appropriate alternation of electric potential in channels
 470 and 472 on the one hand and main channel 420 on the other, precise
 amounts of reagents can be metered into main flowpath 420.
 With regard to electrodes, some or all of the electrodes may be within the
 second plate with external connections to power supplies that may be part
 of an instrument into which the present apparatus is inserted. On the
 other hand, some or all of the electrodes might be on a separate part
 (e.g. built into an instrument into which the present apparatus is
 inserted), such that the electrodes can be immersed into the appropriate
 fluid reservoirs at the time of use. In this approach the electrodes in
 the separate instrument may be adapted to make contact with an appropriate
 lead from each of the reservoirs forming a part of the microfluidic
 networks in the subject apparatus. The electrodes may be strip metal
 electrodes formed in a stamping process or chemical etching process. The
 electrodes may be wires or strips either soldered or glued with epoxy and
 can be made of conductive materials such as platinum, gold, carbon fibers
 and the like. The electrodes could be deposited, coated or plated onto a
 section of the exterior wall of a capillary near each end of the
 capillary. Controlled vapor deposition of gold, platinum, or palladium
 metal onto the exterior wall of the capillary is one method of forming the
 electrodes. This technique can be used to produce an electrode layer with
 a thickness up to several microns. Thicker electrodes could be
 subsequently formed by electrochemically plating gold, palladium or
 platinum onto the thin electrode formed by the vapor deposition process.
 Electrodes could be integral with the second plate formed by silk
 screening process, printing, vapor position, electrode-less plating
 process, etc. Carbon paste, conductive ink, and the like could be used to
 form the electrode. The electrodes may also be present between the plate
 comprising the transfer elements and the attaching element(s).
 Regardless of the embodiment of the present invention that is constructed,
 it is preferable for the electrodes to be connected to an electronic
 computer. The computer has programmed software dedicated to providing the
 moving waves or voltage profile along the channel. Various different types
 of software can be provided so as to obtain the best possible results in
 the particular microfluidic processing conducted.
 It is also within the purview of the present invention that the computer
 software that is connected to the electrodes be made interactive with an
 optical detection device such as ultraviolet or fluorescence spectrometer.
 The spectrometer can be focused singly or at various points along the
 medium in the channels. As the ultraviolet spectrometer reads different
 types of substances being moved to different portions of the medium, the
 information can be sent to the computer, which can adjust the speed of the
 waves or voltage distribution profiles being generated in order to more
 precisely fine tune the resolution of the substances being moved through
 the medium.
 As mentioned above, the channels can be in any shape. More specifically the
 channels can be fashioned so that it has a plurality of branches. Each of
 the branches along with the channel itself can be filled with a desired
 medium. Various reagents may be moved along the branches by utilizing the
 moving electric wave generated by the computer. Accordingly, a
 sophisticated computer program may be utilized to provide for various
 protocols for microfluidic processing such as chemical synthesis,
 sequencing of polynucleotides.
 The apparatus of the present invention may have any convenient
 configuration capable of comprising the device, the microwell plate and so
 forth and their respective component parts. The cavities and channels of
 the microfluidic network are usually present on the surface of a planar
 substrate where the substrate will usually, though not necessarily be
 covered with a cover plate to seal the microfluidic networks present on
 the surface of the planar substrate from the environment. The cover plate
 will have appropriate communication means for establishing communication
 between each of the sample receiving elements of the first plate and the
 corresponding microfluidic network of the second plate. Such means
 include, for example, through-holes, capillaries, porous wicks and the
 like. The apparatus may have a variety of configurations such as, for
 example, rectangular, circular, or other convenient configuration.
 Generally, apparatus in accordance with the present invention are of a
 size that is readily handled and manipulated. In general, a rectangular
 apparatus has dimensions of about 3 inches by 5 inches; a circular
 apparatus has a diameter of about 4 to 16 inches; and each would have a
 thickness of about 0.60 to 1.5 inches (including all of the elements of
 the apparatus). It should be obvious that the size of the present devices
 and apparatus is not critical and is in general a function of the
 particular multiwell plate with which the present device may be used.
 The plate containing the microfluidic networks may be fabricated from a
 wide variety of materials, including glass, fused silica, acrylics,
 thermoplastics, (cross-linked) thermosets and the like. The various
 components of the plate may be fabricated from the same or different
 materials, depending on a number of factors such as, e.g., the particular
 use of the device, economic concerns, solvent compatibility, optical
 clarity, color, mechanical strength, selective strength, surface
 chemistry, method of production, and so forth. For example, the planar
 substrate of the microfluidic network may be fabricated from the same
 material as the cover plate, e.g., polymethylmethacrylate, or from
 different materials such as, e.g., polymethylmethacrylate for the
 substrate and glass for the cover plate.
 For ease of detection and fabrication, the entire apparatus may be
 fabricated form a plastic material that is optically transparent, which
 generally allows light of wavelengths ranging from 180 to 1500 nm, usually
 220 to 800 nm, more usually 450 to 700 nm, to have low transmission
 losses. Suitable materials include fused silica, plastics, quartz, glass,
 and so forth.
 Also of interest as materials suitable for fabrication of microfluidic
 network plate are plastics having low surface charge under conditions or
 electroflow. Particular plastics finding use include polymethylacrylate,
 polycarbonate, polyethylene terephthlate, polystyrene or styrene
 copolymers, polyethylene, polypropylene, polybutadiene, Teflon, silicones,
 and the like.
 The microfluidic network plates may be fabricated using any convenient
 means, including conventional molding and casting techniques. For example,
 with plastic material, a silica mold master which is negative for the
 network structure in the planar substrate of the second plate can be
 prepared by etching or laser micromachining. In addition to having a
 raised ridge which forms the channel in the substrate, the silica mold may
 have a raised area that provides for one or more cavity structures in the
 planar substrate. Next, a polymer precursor formulation can be thermally
 cured or photopolymerized between the silica master and support planar
 plate, such as a glass plate. Where convenient, the procedures described
 in U.S. Pat. No. 5,110,514, the relevant disclosure of which is
 incorporated by reference, may be employed. After the planar substrate has
 been fabricated, the enrichment channel may be placed into the cavity in
 the planar substrate and electrodes introduced where desired. Finally, a
 cover plate may be placed over, and sealed to, the surface of the
 substrate. The cover plate may be sealed to the substrate using any
 convenient means, including ultrasonic welding, adhesives, etc.
 In one approach the microfluidic network plates may have multiple layers
 that are sandwiched together similar to multiple layer electronic printed
 circuit boards. In this approach the plates may be made in a manner
 similar to the printed circuit boards. Each layer contains cavities,
 channels and through-holes. When the various plates are assembled into an
 apparatus, the channels and through-holes in each layer can interconnect
 forming three dimensional fluid circuits. This approach allows
 significantly greater circuit complexity and circuit density than the
 single layer approach.
 Another embodiment of a device in accordance with the present invention is
 shown in FIGS. 9-11. Device 600 comprises a plate 620 having an array of
 transfer elements 622. Transfer elements 622 each comprise a aperture 630
 in plate 620 with a protrusion 632 depending therefrom. In this embodiment
 protrusion 632 is formed in plate 670, which is permanently, non-removably
 attached to plate 620. Plate 670 is manufactured from an electroconductive
 material. Plate 670 is usually about 0.1 to about 10 mm in thickness,
 preferably, about 1 to about 5 mm in thickness. Typically, plate 670 is a
 thin metal foil secured to plate 620 and perforated in a precision manner
 to produce protrusions 632, which has opening 634. Plate 620 comprises
 circumferential opening 672 adjacent each of apertures 630. The function
 of opening 672 is to assist liquid into aperture 630 when the present
 device is utilized. The dimensions of opening 672 are about 0.1 to 5 mm in
 diameter, usually, about 1 to 4 mm in diameter. Plate 620 also comprises
 circumferential rib 674 adjacent opening 672 and in a direction generally
 opposite to protrusions 632. Rib 674 may be integral with plate 620, and
 thus formed from the same material as plate 620, or it may be formed from
 a different material and fixedly attached to plate 620. Rib 674 is used
 for providing sealing removable attachment of plate 620 to a multiwell
 plate 54. Thus, ribs 674 assist in positioning plate 620 with respect to
 multiwell plate 54 and aligning transfer elements 622 with wells 56. Ribs
 674 are each about 1 to about 10 mm, preferably, about 5 to 10 mm, in
 length and about 0.2 to about 2 mm in thickness. Optionally, a removable
 backing (not shown) may be included to protect the ribs during shipment
 and handling.
 As with the device of FIGS. 1-2, the device of FIGS. 9-10 is attached to
 the top 52 of multiwell plate 54 as shown in cross-section in FIG. 11.
 Plate 620 is pressed firmly into place on the top of multiwell plate 54.
 Ribs 674 are inserted into wells 56 and engage side walls 57 thereof
 resulting in a friction fit and sealing removable attachment to wells 56.
 Thus, the construction of plate 620 is such that each of the transfer
 elements 22 are aligned with a corresponding well 56 of multiwell plate
 54.
 Once device 600 is attached to multiwell plate 54, the resulting apparatus
 650 is inverted so that each of the protrusions fills with liquid. A
 meniscus 660 is formed at opening 634. Apparatus 650 is then positioned
 adjacent to an array of sample receiving reservoirs 142, which are part of
 microfluidic networks 108 in a microfluidic network plate 110 as depicted
 in FIG. 11. Each of the microfluidic networks 108 has an electrode 664
 connected to plate 670, of which transfer element 622 is comprised. An
 electric potential is applied across plate 670, which is made of
 conductive material means of electrode 664, which is connected to plate
 670, causing a precise amount of liquid 58 in each of transfer elements
 622 to be forced out of the transfer elements and into a corresponding
 sample receiving reservoir 142.
 The embodiment of FIGS. 9-11 does not require an adhesive, and, thus, there
 is no adhesive to contact the liquid to be transferred. The embodiment
 relies on a press fit of the ribs 674 in the well of a microwell plate.
 Plate 670 may be fabricated inexpensively and eliminates the need to coat
 the aperture or nozzle with an electroconductive material.
 In an alternate embodiment depicted in FIG. 12-14 plate 670 may be composed
 of an electroconductive material in the form of a sheet with nozzle-like
 protrusions. The device depicted in FIGS. 12-14 has an adhesive layer 638
 similar to that in the embodiment depicted in FIGS. 1-3 above. Adhesive
 layer 638 lies above plate 670 and removable backing 626 lies above 638.
 An array of through-holes 637 are present in adhesive layer 638 generally
 corresponding in location and centered with respect to the array of
 apertures 630.
 In use, backing 626 is removed from plate 670, which is then attached to
 the top 52 of multiwell plate 54 having an array of wells 56 containing
 liquid 58. Plate 670 is pressed firmly into place on the top of multiwell
 plate 54 so that outer lip 621 fits snugly into cut out area 51, which
 extends around the periphery of plate 54. Adhesive layer 638 is pressed
 firmly against the front side 52 of multiwell plate 54. The construction
 of plate 670 is such that each of the transfer elements 622 are aligned
 with a corresponding well 56 of multiwell plate 54. Once device 601 is
 attached to multiwell plate 54, the resulting apparatus 651 is inverted so
 that each of the apertures 630 fills with liquid. A meniscus 660 is
 formed.
 Another embodiment of the present invention is depicted in FIGS. 15-17.
 This approach is based on the use of flexible circuit technology. The
 device 700 comprises supporting film 710 to which conductive traces 712
 are attached. Supporting film 710 may be fabricated from polymer films
 such as mylar, kapton, etc., and the like. Backing film 720 is layered
 below conductive traces 712, which extend to the inside surface of
 aperture 730 in backing film 720. Backing film 720 is fabricated from
 polymer films such as mylar, kapton, etc., and the like and has
 through-holes 730, which are plated with an electroconductive material at
 732. Conductive traces 712 are printed conductive ink, vacuum deposited
 metal, plated metal, and the like. Below backing film 720 is cover film
 724 with a through-hole corresponding to 730. Cover film 724 is fabricated
 from polymer films such as mylar, kapton, etc., and the like. Above
 supporting film 710 is adhesive layer 738 with opening 737, which is
 larger than, and centered on, through-hole 730. Above adhesive 738 is
 removable backing 726. The above device may be constructed in a manner
 similar to that disclosed in U.S. Pat. Nos. 4,626,462, 4,675,786 and
 4,715,928, the relevant disclosures of which are incorporated herein by
 reference.
 In use, backing 726 is removed from device 700, which is then attached to
 the top 52 of multiwell plate 54 having an array of wells 56 containing
 liquid 58. Adhesive layer 738 is pressed firmly against the front side 52
 of multiwell plate 54. The construction of device 700 is such that each of
 through-holes 730 is aligned with a corresponding well 56 of multiwell
 plate 54. Once device 700 is attached to multiwell plate 54, the resulting
 apparatus 750 is inverted so that each of the apertures 730 fills with
 liquid. A meniscus 760 is formed.
 VII. As shown in FIG. 18, an acceleration (or ring) electrode 802 may be
 used to assist in dispensing liquid where the distance between the
 aperture 730 and the sample receiving reservoir 142 may substantially
 affect the dispensing operation. Such acceleration electrodes have been
 used in other applications. See, for example, U.S. Pat. No. 5,278,583, the
 relevant portions of which are incorporated herein by reference. The
 acceleration electrode may be placed between the aperture and the sample
 receiving reservoir. If desired, a bias voltage can be applied between the
 electrode associated with the aperture and the electrode associated with
 the sample receiving reservoir. To cause dispensing of liquid, a pulsed
 voltage is applied between the acceleration electrode and the aperture,
 causing droplets to be accelerated out from the aperture towards the hole
 in the acceleration electrode. The timing of the pulse should be adjusted
 so that droplets are not inadvertently pulled sideways onto the
 acceleration electrode as they pass through the hole.
 VIII. In another embodiment, as shown in FIG. 19, the present invention may
 be employed in conjunction with capillary size dispensing tubes 804
 associated with the apertures 703 of the present devices. The capillary
 tubes are used to form small drops of fluid and locate them precisely on
 substrate surfaces 142 in miniature arrays. The printed arrays may consist
 of nucleic acids, peptides, immunoassay reagents, pharmaceutical test
 compounds and the like. As shown in FIG. 20, the array 900 of capillary
 dispensing tubes in fluid communication with the array of source wells may
 be used to locate the drops on a substrate in predetermined patterns.
 Nanoliter quantities of liquids may be dispensed. Arrays of biological
 samples as dense as approximately sixteen hundred per square centimeter
 with center to center spacing as small as about two hundred fifty
 micrometers may be formed.
 The length and the bore diameter of the dispensing capillary control the
 volume of liquid drawn into the dispensing capillary. Those skilled in the
 art will recognize a large number of capillaries useful for practicing
 this invention. For example, fused silica may be used with an outside
 coating of polyimide for strengthening with inside bore ID's from about 10
 to 200 microns, more typically from about 25 to 100 microns and OD's
 greater than about 200 microns. Typically, the length of the dispensing
 capillary could range up to about 10 to 20 mm. Dispensing capillaries of
 these dimensions can fill with sample volumes in the 1 to 10 microliter
 range. The volume of liquid drawn into the dispensing capillary can be
 controlled by defining the bore diameter and the length of the dispensing
 capillary. The latter dimension can be defined by positioning a stop
 junction along the inner wall of the dispensing capillary. This stop
 junction could be an abrupt increase in the bore diameter of the
 dispensing capillary. Alternatively, surface treatment procedures may be
 used for controlling the amount of liquid the dispensing capillary can
 hold.
 In a preferred embodiment, the dimensions of the capillaries are about
 0.001 to 0.020 inches in diameter, preferably 0.005 to 0.01 inches in
 diameter, preferably, about 100 micrometers inner diameter and about 250
 micrometers outer diameter. The dimensions of the resulting spots are
 about 125 micrometers diameter with a center to center spacing of 250
 micrometers. The resulting array has a density of about 1600 per square
 centimers.
 In another approach an electrically conducting collar is deposited to a
 capillary. One end of the capillary is attached to the device of the
 invention through a liquid filled line and the other end of the capillary
 is for dispensing. When a voltage is applied to the collar, it
 electrostatically sprays a defined volume of liquid. The volume of the
 drop is dependent upon a number of factors that include the diameter of
 the capillary, the viscosity of the liquid, the intensity and the duration
 of the voltage pulse and so forth. A single voltage pulse produces a drop
 of approximately 200 picoliters. With a frequency of about 1000 pulses per
 second, a volume of about 0.2 microliters per second will be delivered.
 A particular device in accordance with the above embodiment has a sample
 handling plate with an array of sample handling wells, which contain
 liquid samples, with a corresponding array of capillaries extending from
 the aperture of the sample handling plate. When the dispensing capillaries
 are in the sample, an aliquot of sample is transferred to the dispensing
 capillary by combination of electrostatic and capillary action. The device
 comprises a plate having an array of transfer elements, each of which
 comprises an aperture in the plate with a protrusion depending therefrom.
 In this embodiment the protrusion is formed in the plate, which is
 permanently, non-removably attached to the plate. The plate is
 manufactured from an electroconductive material and is usually about 0.1
 to about 10 mm in thickness, preferably about 1 to about 5 mm in
 thickness. In a particular embodiment the plate is a thin metal foil
 secured to the plate and perforated in a precision manner to produce the
 protrusions with openings. Each opening contains a hollow capillary tube
 with a channel. The dimensions of the channel will depend on the
 dimensions of the transfer elements or of a microfluidic system.
 As mentioned above, in the present invention an array of samples in a
 multiwell source plate are simultaneously transferred to an array of
 microassay reservoirs of plate comprising an array of microfluidic
 networks by means of a device having a plurality of transfer elements. The
 microfluidic network plate contains 96, 384, or 1536 receiving reservoirs
 or sites on its bottom surface. These reservoirs are connected to mixing,
 reaction, and separation channels in the microfluidic network plate. The
 present device contains an active liquid transfer means over each well of
 a multiwell plate such as a source or library plate, to which the present
 device is attached. Upon activation, the transfer elements in the present
 device move an amount of liquid from the wells of the library plate to the
 microfluidic network plate, in which the sample processing and analysis
 take place. The present devices are attached to the library plate after
 the source plate is created and stays attached during normal use. In the
 present invention there is no element that is immersed in the sample to be
 processed. The present device alleviates debris contamination and prevents
 evaporation of the liquid in the wells.
 Once the samples have been transferred in accordance with the present
 invention to a microfluidic network, the samples may be processed. A
 sample may be processed by one or more of any number of procedures such
 as, for example, separating or classifying compounds, replicating or
 amplifying components, degrading components, polymerizing components, and
 other similar modifications, and so forth. Examples of such procedures
 include subjecting such sample to separation procedures for sample
 enrichment, isolation or purification, analyzing such sample such, e.g.,
 as an assay, detection and the like, carrying out a chemical synthesis
 with such sample, such as those involved with combinatorial chemistry
 methods for small and large molecule synthesis, screening for therapeutic
 drugs, receptor-ligand binding analysis, screening for agonist/antagonist
 behavior of compounds, DNA and protein sequencing, genotyping,
 oligosaccharide profiling, and so forth. For example, polynucleotides may
 be synthesized or sequenced. Different nucleotides can be reacted to form
 DNA and different amino acids can be reacted to form proteins. These
 reactions can be carried out at greatly increased speeds as compared with
 conventional mechanical technologies. In addition to increased speeds, the
 yield is vastly improved due to the precision with which the reactants can
 be moved in accordance with the present invention.
 Reactions may include catalytic and affinity reactions. Although enzymes
 are the typical biocatalyst employed for bioanalytical applications,
 catalytic antibodies and catalytic RNA are also to be included, among
 others. Affinity-based reactions may include, but are not limited to,
 receptor-mediated ligand binding, DNA or RNA hybridization, and
 immuno-reactions. The later is not limited to antibody-antigen
 interactions and can include antibody-hapten, antibody-nucleic acid
 binding, antibody-antibody interactions, and antibody-receptor binding.
 In addition to the separation, synthesis and sequencing methods described
 above, the present invention is useful for a variety of additional
 purposes. For example, it is possible to utilize specific embodiments of
 the invention in order to separate impurities from large mixtures of
 compounds and thus carry out a purification processing which is
 substantially more refined than vacuum fractionation processing. A mixture
 of components can be separated into a variety of pure groups and moved
 along parallel tracks. Upon resolving the mixtures, the desired components
 can be guided by the electrical fields to appropriate locations within one
 or more channels. Alternatively, selected components may be guided to
 channels filled with members of binding pairs, such as antigen-antibody
 pairs, reactive with given substances of interest. These substances of
 interest may be moving in the medium or be moved into contact with
 complementary components having a label, other member of a signal
 producing system, or other type of chemical for various transformations
 that are either physical or chemical in nature. Furthermore, bacterial or
 mammalian cells, or viruses may be sorted by complicated microfluidic
 networks in connection with a plurality of electrodes capable of
 generating electrical potentials of a variety of different strengths in
 order to move the cells, organelles, liposomes, and the like, or viruses,
 through the fields based on the size, charge or shape of the particular
 material being moved. Separated cells or viruses may be analyzed or
 modified subsequently, for example, by disruption to analyze or otherwise
 characterize its internal components.
 The processing is generally carried out on a microfluidic scale with
 channel dimensions similar to those used typically in capillary
 electrophoresis. However, there may be regions with larger than
 capillary-scale dimensions for purposes of increasing surface area
 reaction volume, accommodating highly dilute sample or interfacing with
 existing equipment. The miniaturized system of enrichment trenches,
 reaction chambers and detection zones enable multiple laboratory processes
 to be integrated "on-board" a planar substrate, including sample
 preparation, incubation, electrophoretic separations, and analyses.
 The sample is usually a medium containing a substance of interest,
 synthetic or natural, to be examined, treated, determined or otherwise
 processed. Typical sources for mammalian biological samples include body
 fluids such as, for example, whole blood, blood fractions such as serum
 and plasma, synovial fluid, cerebro-spinal fluid, amniotic fluid, semen,
 cervical mucus, sputum, saliva, gingival fluid, urine, and the like. Other
 sources include culture samples, bioprocessing fluids, food and beverage
 water, air and soil samples, and so forth. In addition, sample includes
 combinatorial chemistry generated libraries of compounds, usually small
 molecules, oligonucleotides and peptides. Other sources of samples are
 aqueous or water soluble solutions of natural or synthetic compounds,
 particularly, compounds that are potential therapeutic drugs where it is
 desired to determine if the compound binds to a specific receptor.
 The amount of the sample depends on the nature of the sample and the nature
 of the processing to be conducted. For fluid samples such as whole blood,
 saliva, urine and the like the amount of the sample is usually about 1 to
 1000 nanoliters, more usually, about 10 to 100 nanoliters. The sample can
 be pretreated and can be prepared in any convenient medium, which does not
 interfere with a microfluidic process in accordance with the present
 invention. An aqueous medium is preferred.
 The substance can be comprised of a member of a specific binding pair (sbp)
 and may be a ligand, which is monovalent (monoepitopic) or polyvalent
 (polyepitopic), synthetic or natural, antigenic or haptenic, and is a
 single compound or plurality of compounds which share at least one common
 epitopic or determinant site. The substance of interest can be a part of a
 cell such as bacteria or a cell bearing a blood group antigen such as A,
 B, D, etc., or an HLA antigen, or cell membrane receptors, or a
 microorganism, e.g., bacterium, fungus, protozoan, or virus.
 The monoepitopic ligands will generally be from about 100 to 2,000
 molecular weight, more usually from 125 to 1,000 molecular weight. The
 substances of interest include drugs, potential drug candidates,
 metabolites, pesticides, pollutants, and the like. The polyvalent ligands
 will normally be poly(amino acids), i.e., polypeptides and proteins,
 polysaccharides, nucleic acids, and combinations thereof. Such
 combinations include components of bacteria, viruses, chromosomes, genes,
 mitochondria, nuclei, cell membranes and the like. For the most part, the
 polyepitopic ligands to which the subject invention can be applied will
 have a molecular weight of at least about 5,000, more usually at least
 about 10,000. In the poly(amino acid) category, the poly(amino acids) of
 interest will generally be from about 5,000 to 5,000,000 molecular weight,
 more usually from about 20,000 to 1,000,000 molecular weight; among the
 hormones of interest, the molecular weights will usually range from about
 5,000 to 60,000 molecular weight.
 For receptors, the molecular weights will generally range from 10,000 to
 2.times.108, more usually from 10,000 to 106. For immunoglobulins, IgA,
 IgG, IgE and IgM, the molecular weights will generally vary from about
 160,000 to about 106. Enzymes will normally range from about 10,000 to
 1,000,000 in molecular weight. Natural receptors vary widely, generally
 being at least about 25,000 molecular weight and may be 106 or higher
 molecular weight, including such materials as avidin, DNA, RNA, thyroxine
 binding globulin, thyroxine binding prealbumin, transcortin, etc.
 Also included are polynucleotides such as m-RNA, r-RNA, t-RNA, DNA, DNA-RNA
 duplexes, etc. The term analyte also includes receptors that are
 polynucleotide binding agents, such as, for example, restriction enzymes,
 activators, repressors, nucleases, polymerases, histones, repair enzymes,
 chemotherapeutic agents, and the like.
 A member of a specific binding pair ("sbp" member) is generally one of two
 different molecules having an area on the surface or in a cavity that
 specifically binds to and is therefore defined as complementary with a
 particular spatial and polar organization of the other molecule. The
 members of the sbp can be referred to as ligand and receptor such as
 members of an immunological pair, e.g., antigen-antibody. Complementary
 sbp members bind to one another, as for example, a ligand and its
 complementary receptor. With respect to two complementary sbp members, one
 may be referred to as the "binding partner" for the other. Sbp members can
 be immunological pairs such as antigen and antibody, or non-immunological
 pairs such as avidin and biotin. Sbp members can also be small molecules
 or residues of small molecules and their receptors. Small molecules have a
 molecular weight of from 100-2000, preferably 150-1000, and a receptor for
 the small molecule either exists or can be prepared. Examples of small
 molecules include derivatives of biotin, lysergic acid, fluorescein or a
 fluorescein derivative, and vitamin B12, with the corresponding receptors
 being avidin or streptavidin, anti-lysergic acid, anti-fluorescein and
 intrinsic factor, respectively.
 The ligand is any organic compound for which a receptor naturally exists or
 can be prepared. Receptors ("antiligand") are any compound or composition
 capable of recognizing a particular spatial and polar organization of a
 molecule, e.g., epitopic or determinant site. Illustrative receptors
 include membrane bound receptors such as G-protein receptors (e.g.,
 muscarinic, adrenergic, prostaglandin and dopamine such as the D2
 receptor), tyrosine kinase (insulin-like IGF, epidermal EGF, nerve NGF,
 fibroblast FGF growth factors), ion channels, T-cell receptors, the
 interleukins, and other naturally occurring receptors, e.g., thyroxine
 binding globulin, antibodies, enzymes, Fab fragments, lectins, nucleic
 acids, protein A, complement component C1q, and the like.
 In an assay and in screening methods it is often desirable to use a label
 or reporter molecule, which is a chemical entity capable of being detected
 by a suitable detection means, including, but not limited to,
 spectrophotometric, chemiluminescent, electrochemical or radiochemical
 means. The reporter molecule can be conjugated to another molecule such as
 an sbp member, e.g., a ligand or an antibody, by procedures well known in
 the art. Typically, the reporter molecule contains a functional group
 suitable for attachment to the sbp member. The functional groups suitable
 for attaching the reporter group are usually activated esters or
 alkylating agents. Details of techniques for attaching reporter groups are
 well known in the art. See, for example, Matthews, et al., Anal. Biochem.
 (1985) 15:205-209 and Engelhardt, et al., European Patent Application No.
 0302175.
 Reporter molecules are members of a signal producing system capable of
 being detected directly or through a specific binding reaction to produce
 a detectable signal. The reporter molecule can be isotopic or nonisotopic,
 usually nonisotopic, and can be a catalyst, dye, fluorescent molecule,
 chemiluminescent molecule, coenzyme, enzyme, substrate, radioactive group,
 certain particles such as carbon and the like.
 The labels or reporter molecules are usually part of a signal producing
 system ("sps"). The label and optionally other sps members are bound to an
 sbp member. Preferably, the label is an enzyme, electroluminescent group
 such as a transition metal complex (see, e.g., U.S. Pat. Nos. 5,541,113,
 5,610,017, 5,527,710, 5,591,581, the relevant disclosures of which are
 incorporated herein by reference, chemiluminescer, fluorescer, radiolabel,
 or the like. Thus, with the above labels the signal is preferably detected
 and/or measured by detecting enzyme activity, luminescence, or light
 emissions, respectively. The labels and other reagents of the signal
 producing system must be stable at the temperatures used in the
 electroseparation method and subsequent assay.
 Suitable labels include, by way of illustration and not limitation, enzymes
 such as alkaline phosphatase, glucose-6-phosphate dehydrogenase ("G6PDH")
 and horseradish peroxidase; promoters; dyes; fluorescers, such as
 fluorescein, isothiocyanate, rhodamine compounds, phycoerythrin,
 phycocyanin, allophycocyanin, o-phthaldehyde, and fluorescamine;
 electroluminescent labels such as ruthenium chelates; chemiluminescers
 such as isoluminol; sensitizers; coenzymes; enzyme substrates; radiolabels
 such as 125I, 131I, 14C, 3H, 57Co and 75Se. Suitable enzymes and coenzymes
 are disclosed in Litman, et al., U.S. Pat. No. 4,275,149, columns 19-28,
 and Boguslaski, et al., U.S. Pat. No. 4,318,980, columns 10-14; suitable
 fluorescers and chemiluminescers are disclosed in Litman, et al., U.S.
 Pat. No. 4,275,149, at columns 30 and 31; which are incorporated herein by
 reference.
 Some labels can directly produce a signal, and therefore, additional
 components are not required to produce a signal. Numerous organic
 molecules, for example fluorescers, are able to absorb ultraviolet and
 visible light, where the light absorption excites these molecules to an
 excited energy state. This absorbed energy is then dissipated by emission
 of light at a second wavelength. Other labels that directly produce a
 signal include radioactive isotopes and dyes.
 Alternately, the label may need other components to produce a signal. In
 this situation the signal producing system would then include all the
 components required to produce a measurable signal. These components may
 include substrates, electron transfer agents, coenzymes, enhancers,
 additional enzymes, substances that react with enzymic products,
 catalysts, activators, cofactors, inhibitors, scavengers, metal ions, and
 a specific binding substance required for binding of signal generating
 substances. A detailed discussion of suitable signal producing systems can
 be found in Ullman, et al. U.S. Pat. No. 5,185,243, columns 11-13,
 incorporated herein by reference.
 The label can be bound covalently to numerous sbp members: an antibody; a
 receptor for an antibody; a receptor that is capable of binding to a small
 molecule conjugated to an antibody, a ligand analog, an oligonucleotide
 and the like. Bonding of the label to the sbp member may be accomplished
 by chemical reactions that result in replacing a hydrogen atom of the
 label with a bond to the sbp member or may include a linking group between
 the label and the sbp member. Other sps members may also be bound
 covalently to sbp members such as avidin-biotin,
 fluorescein-anti-fluorescein, and the like. Two sps members such as a
 fluorescer and quencher can each be bound to a different antibody that
 forms a specific complex with the analyte. Formation of the complex brings
 the fluorescer and quencher in close proximity, thus permitting the
 quencher to interact with the fluorescer to produce a signal. Methods of
 conjugation are well known in the art. See for example, Rubenstein, et
 al., and U.S. Pat. No. 3,817,837, incorporated herein by reference.
 Alternatively, one label may be bound to the particles of this invention
 and a second label bound to a sbp member that binds to the sbp member
 attached to the particle.
 As mentioned above, the microfluidic processing includes assays. Generally,
 an assay is a method for determining a substance capable of binding to a
 specific binding pair member, for example, for determining an analyte or
 detecting the degree of binding of a compound to a receptor. The
 determination may be qualitative or quantitative. Such assays depend on
 specific binding of a ligand to its receptor and include receptor binding
 assays, immunoassays, ligand/binding assays, polynucleotide assays,
 particularly polynucleotide hybridization assays, and cell surface binding
 assays. The assays may be utilized for drug discovery and screening,
 studies of receptors, detection of drugs and other substances, DNA
 detection, DNA sequencing, genetic analysis, monitoring of gene
 expression, and so forth. One particular assay is the immunoassay, which
 is a specific binding assay in which the reagents include an antibody.
 Antibodies are immunoglobulins that specifically bind to, and are thereby
 defined as complementary with, a particular spatial and polar organization
 of another molecule. The antibody can be monoclonal or polyclonal and can
 be prepared by techniques that are well known in the art such as
 immunization of a host and collection of sera (polyclonal) or by preparing
 continuous hybrid cell lines and collecting the secreted protein
 (monoclonal), or by cloning and expressing nucleotide sequences or
 mutagenized versions thereof coding at least for the amino acid sequences
 required for specific binding of natural antibodies. Antibodies may
 include a complete immunoglobulin or fragment thereof, which
 immunoglobulins include the various classes and isotypes, such as IgA,
 IgD, IgE, IgG1, IgG2a, IgG2b and IgG3, IgM, etc. Fragments thereof may
 include Fab, Fv and F(ab')2, Fab', and the like. In addition, aggregates,
 polymers, and conjugates of immunoglobulins or their fragments can be used
 where appropriate so long as binding affinity for a particular molecule is
 maintained.
 The assays may be heterogeneous or homogeneous. A heterogeneous assay is an
 assay wherein free labeled species is separated from a labeled species
 that is bound to another species such as an sbp member. The separation may
 be carried out by physical separation, e.g., by transferring one of the
 species to another reaction vessel, filtration, centrifugation,
 chromatography, solid phase capture, magnetic separation, and so forth and
 may include one or more washing steps. The separation may be nonphysical
 in that no transfer of one or both of the species is conducted, but the
 species are separated from one another in situ. In the heterogeneous assay
 the activity of a label is not affected by the reaction of specific
 binding pair members with one another. Regardless of the means of
 separation, the signal from the label may be measured from one or both of
 the separated species.
 A homogeneous assay is an assay wherein free labeled species is not
 separated from a labeled species that is bound to another species such as
 an sbp member. The signal from the label is significantly different
 between the free labeled species and that which is bound and, thus, can be
 measured without separation.
 Another aspect of the present invention comprises kits for processing a
 sample. In one embodiment a kit comprises a device or an apparatus as
 described above and reagents, other than reagents within the apparatus,
 for processing a sample. The kit may also include one or more microfluidic
 network plates. The reagents for the kits may be packaged in the same or
 separate containers, so that the concentration of the reagents provides
 for substantial optimization of the method and assay. The reagents may
 each be in separate containers or various reagents can be combined in one
 or more containers depending on the cross-reactivity and stability of the
 reagents. Under appropriate circumstances one or more of the reagents in
 the kit can be provided as a dry powder, usually lyophilized, including
 excipients, which on dissolution will provide for a reagent solution
 having the appropriate concentration for performing a method or assay in
 accordance with the present invention. The kit can also include additional
 reagents depending on the nature of the method for which the kit is used.
 For example, the kit may include solid phase extraction materials
 including paramagnetic beads and non-magnetic particles, lysis solutions,
 wash and elution and running buffers, biomolecular recognition elements
 including receptors, enzymes, antibodies and other specific binding pair
 members, labelling solutions, substrates, reporter molecules, sample
 purification materials including membranes, beads, and the like, and so
 forth.