Abstract:
A manifold for connecting external capillaries to the inlet and/or outlet ports of a microfluidic device for high pressure applications is provided. The fluid connector for coupling at least one fluid conduit to a corresponding port of a substrate that includes: (i) a manifold comprising one or more channels extending therethrough wherein each channel is at least partially threaded, (ii) one or more threaded ferrules each defining a bore extending therethrough with each ferrule supporting a fluid conduit wherein each ferrule is threaded into a channel of the manifold, (iii) a substrate having one or more ports on its upper surface wherein the substrate is positioned below the manifold so that the one or more ports is aligned with the one or more channels of the manifold, and (iv) device to apply an axial compressive force to the substrate to couple the one or more ports of the substrate to a corresponding proximal end of a fluid conduit.

Description:
This invention was made with Government support under Contract No. DE-AC04-94AL85000 awarded by the U.S. Department of Energy to Sandia Corporation. The Government has certain rights to the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to microfluidic systems and more particularly to structures which facilitate the introduction of fluids into devices having microfluidic channels. 
     BACKGROUND OF THE INVENTION 
     Devices for performing chemical analysis have in recent years become miniaturized. For example, microfluidic devices have been constructed using microelectronic fabrication and micromachining techniques on planar substrates such as glass or silicon which incorporate a series of interconnected channels or conduits to perform a variety of chemical analysis such as capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). 
     Microfluidic substrates have networks of chambers connected by channels which have mesoscale dimensions, where at least one dimension is usually between 0.1 microns and 500 microns. Such microfluidic substrates may be fabricated using photolithographic techniques similar to those used in the semi-conductor industry, and the resulting devices can be used to perform a variety of sophisticated chemical and biological analytical techniques. Microfluidic analytical technology has a number of advantages, including the ability to use very small sample sizes, typically on the order of nanoliters. The substrates may be produced at a relatively low cost, and can be formatted to perform numerous specific analytical operations, including mixing, dispensing, valving, reactions, and detections. 
     Another recently developed class of sample-receiving microfluidic substrates includes substrates having a capillary interface that allows compounds to be brought onto the test substrate from an external source, and which can be advantageously used in a number of assay formats for high-throughput screening applications. These assay formats include fluorogenic assays, fluorescence polarization assays, non-fluorogenic mobility shift assays, dose response assays, and calcium flux cell-based assays. 
     Other applications for microfluidic devices include diagnostics involving biomolecules and other analytical techniques such as micro total analysis systems. Such devices, often referred to in the art as “microchips,” also may be fabricated from plastic, with the channels being etched, machined or injection molded into individual substrates. Multiple substrates may be suitably arranged and laminated to construct a microchip of desired function and geometry. In all cases, the channels used to carry out the analyses typically are of capillary scale dimension. 
     To fully exploit the technological advances offered by the use of microfluidic devices and to maintain the degree of sensitivity for analytical techniques when processing small volumes, e.g., microliters or less, connectors which introduce and/or withdraw fluids, i.e., liquids and gases, from the device, as well as interconnect microfluidic devices, are a crucial component in the use and performance of the microfluidic device. 
     A common technique used in the past involves bonding a length of tubing to a port on the microfluidic device with epoxy or other suitable adhesive. Adhesive bonding is unsuitable for many chemical analysis applications because the solvents used attack the adhesive which can lead to channel clogging, detachment of the tubing, and/or contamination of the sample and/or reagents in or delivered to the device. Furthermore, adhesive bonding results in a permanent attachment of the tubing to the microfluidic device which makes it difficult to change components, i.e., either the microfluidic device or the tubing, if necessary. Thus assembly, repair and maintenance of such devices become labor and time intensive, a particularly undesirable feature when the microfluidic device is used for high throughput screening of samples such as in drug discovery. 
     To avoid problems associated with adhesive bonding, other techniques have been proposed in the past, e.g., press fitting the tubing into a port on the microfluidic device. However, such a connection typically is unsuitable for high-pressure applications such as HPLC. Additionally, pressing the tubing into a port creates high stress loads on the microfluidic device which could lead to fractures of the channels and/or device. 
     Other methods involved introducing liquids into an open port on the microfluidic device with the use of an external delivery system such as a pipette. However, this technique also is undesirable due to the possibility of leaks and spills which may lead to contamination. In addition, the fluid is delivered discretely rather than continuously. Moreover, the use of open pipetting techniques does not permit the use of elevated pressure for fluid delivery such as delivered by a pump, thereby further restricting the applicability of the microfluidic device. 
     Microfluidic devices generally comprise an array of micron-sized wells or reservoirs and interconnecting channels disposed on a substrate. The wells are connected to distribution means for dispensing fluids to and collecting fluids from the array. Connection to the wells is typically by means of a micropipette end. While this serves for benign addition of fluids this means of fluid addition cannot be used for those applications where the access ports are exposed to a pressure differential or where it is desired to connect capillary tubes to fluid wells. 
     Therefore, a need exists for an improved microfluidic connector which is useful with all types of microfluidic devices and provides an effective, high pressure, low fluid dead volume seal. Specifically, there is a need for the connector that functions as a manifold which enables a combination of now streams from a plurality of input capillaries to channel into a single capillary tube or splitting a flow stream, from a single capillary into a multiple flow streams. Finally, it is desirable that the connector has negligible dead volume. 
     SUMMARY OF THE INVENTION 
     The invention is based in part on the development of a manifold for connecting external capillaries to the inlet and/or outlet ports of a microfluidic device for pressure applications. 
     In one aspect, the invention is directed to a fluid connector for coupling at least one fluid conduit to a corresponding port of a substrate that includes: 
     a manifold comprising one or more channels extending therethrough wherein each channel is at least partially threaded; 
     one or more threaded ferrules each defining a bore extending therethrough with each ferrule supporting a fluid conduit wherein each ferrule is threaded into a channel of the manifold; 
     a substrate having one or more ports on its upper surface wherein the substrate is positioned below the manifold so that the one or more ports is aligned with the one or more channels of the manifold; and 
     means for applying an axial compressive force to the substrate to couple the one or more ports of the substrate to a corresponding proximal end of a fluid conduit. 
     In one preferred embodiment, the fluid connector includes: 
     a base plate that is rigidly fastened to and spaced apart from the manifold and which is positioned below the substrate; and 
     a pressure plate that is interposed between the substrate and the base plate wherein the pressure plate includes one or more adjustable screws for maintaining an upward axial force on the substrate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1,  2  and  3  are perspective, front elevational, and side elevational views, respectively, of one embodiment of the edge compression manifold device; 
     FIG. 4 is a cross sectional view of the manifold section of the device shown in FIGS. 1-3; and 
     FIGS. 5-8 are various views of a ferrule. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is directed to techniques for connecting multiple external capillary tubes to the microchannels of a microscale analytic device. The invention is particularly suited for analysis operations that are desirably carried out on microscale devices and that require the application of high pressures. The compression manifold device is expected to withstand pressures of up to at least about 500 psi. As used herein, “microfluidic” channel, or “microchannel” is a channel, e.g., sealed enclosed groove, depression, tube, capillary which is adapted to handle small volumes of fluid. Typically, the microchannel has at least one subsection with at least one cross-sectional dimension of between about 0.1 microns and 500 microns, and typically less than 100 microns. 
     FIGS. 1,  2 , and  3  illustrate an edge compression manifold device  10  for connecting external liquid flow streams to a substrate  20  which can be any preferably substantially planar microfluidic member that has an integrated network of microfluidic channels (not shown) disposed therein. The particular design or configuration of the internal structure of the substrate is not critical. Such substrates are also referred as microfluidic wafers or chips. The substrate is preferably fabricated from glass, quartz, silicon or plastic by conventional techniques including LIGA (an acronym for the German for lithography, electroplating, and molding), deep x-ray lithography, silicon surface micromachining and lithography, electric discharge machining, and direct laser additive fabrication. In addition, commercially available substrates can be modified with appropriate dimensioned inlet and/or outlet ports as further described herein. The substrate may include reaction cells, reservoirs, and other structures that are interconnected by a network of microchannels and a series of micropumps. Such substrates are further described, for example, in U.S. Pat. No. 5,846,396 to Zanzuchi, et al., which is incorporated herein. 
     Substrate  20  includes a plurality of inlet and/or outlet ports  22  that enable fluid communication with mircochannels within the substrate. For example, one or more of ports  22  can be employed as inlet to introduce reagents and cleaning solvents into substrate  20  while other ports  22  can be employed as outlets to remove products and solvents following a flush of the system. Inlet ports can be connected to the appropriate sources of reagents through external capillaries and pumps. Conventional mechanical pumps can be employed although a preferred method employs a high pressure hydraulic system that has no moving parts for converting electric potential to hydraulic force and for manipulating fluids which are described in U.S. Pat. Nos. 6,013,164 to Paul, et al., 6,019,882 to Paul, et al., 6,224,728 to Oborny and 6,277,257 and 6,290,909 both to Paul, et al., which are incorporated herein by reference. 
     Device  10  further includes manifold  12 , base plate  16 , and movable slide pressure plate  14  which is positioned between manifold  12  and base plate  16 . As shown in further detail in the cross sectional view of FIG. 4, the manifold  12  includes a plurality of threaded, tapered channels  36  that run through the manifold. Each threaded channel  36  has an upper aperture  32  on the upper surface of manifold  12  and a lower aperture  24  on the lower surface of manifold. Concentric with each lower aperture  24  on the underside of manifold  12  is a groove that is fitted with an O-ring  28  that provides a fluid-tight seal between substrate  20  and manifold  12 . The O-rings can be made of any suitable deformable material such as natural rubber or silicone. 
     As shown in FIG. 1, the threaded channels are preferably arranged within manifold so that the upper apertures  32  are sufficiently spaced apart for easy access. As is evident, the staggered arrangement for upper apertures  32  has a corresponding staggered arrangement for lower apertures  24  on the manifold&#39;s lower surface. Preferably, the manifold is made of a material such as polyether ether ketone (PEEK) or other suitable polymer. 
     Substrate  20  is disposed or inserted between slide pressure plate  14  and manifold  12  which is fastened to base plate  16  by screws  26 . Substrate  20  has an array of outlet and/or inlet ports  22  on its surface which are connected to an integrated network of microfluidic channels (not shown) within substrate  20 . As shown in FIG. 3, in this embodiment, base plate  16  has an “L” configuration with a back support region  38  that abuts the lower surface of manifold  12 . Base plate  16  also supports slide pressure plate  14 . As discussed above, the lower surface of manifold  12  includes an arrangement of lower apertures  24 . 
     To use the inventive edge the compression manifold, at least one of the lower apertures  24  (FIG. 4) of manifold  12  should be aligned with one of the ports  22  of substrate  20 . In one embodiment, a dedicated manifold can be configured with a specific array of lower apertures  24  whose pattern that matches an array of ports  22  of a particular substrate so that all the ports  22  are aligned with corresponding lower apertures  24 . In this fashion, different substrates can be identified by their specific port arrangements. Using dedicated manifolds avoids mismatching manifolds with different substrates. Alternatively, an edge compression manifold can have different sets of array of lower aperture patterns to accommodate different susbstrates each with different port arrangements. 
     As shown in FIG. 2, one or more guide pins  18  are disposed on either end of base plate  16  to position slide pressure plate  14  properly into place. One or more screws  46  are mounted into base plate  16 ; by tightening these screws slide plate  14  exerts an upward force on substrate  20 . This pressure compresses substrate  20  against the underside of manifold  12  thus compressing o-rings  28 . Preferably, base plate  16  and slide plate pressure  14  are made of a rigid material such as metal, e.g., stainless steel, or hard plastic. 
     FIGS. 5 and 6 show a threaded ferrule  50  that is designed to be screwed into threaded tapered channel  36  of manifold  12  (FIG.  4 ). The ferrule includes an upper handle  54 , an externally threaded middle portion  56 , and a lower tapered end  58 . Ferrule  50  also has internal bore  62  that runs the length of the ferrule from inlet  52  to outlet  60 . As shown in FIG. 6, internal bore  62  is preferably narrower at the tapered end (as compared to the upper handle) of the ferrule so that while a capillary tube can readily fit into the narrower portion of the bore, the wall of the bore at the tapered end will collapse against the capillary tube as compressive forces are created as the ferrule is screwed into the thread tapered channel  36  of manifold  12  (FIG.  4 ). This effectively prevents the capillary tube from extruding during high pressure operations and forms a fluid seal. Preferably each ferrule is constructed as a single, integral piece with no mating sleeve. They can be fabricated by machining a single block of deformable material such as PEEK. 
     When using external capillaries, one end of the capillary is preferably inserted into bore  62  of ferrule  50  until the end of the capillary tube reached outlet  60  of the ferrule or slightly beyond outlet  60 . The other end of the capillary is connected to a source of regent, solvent, or disposable chamber, as the case may be. In this fashion, one end of the capillary will be adjacent to or inside inlet/outlet port  22  of substrate  20  (FIG.  1 ). In another one embodiment, rather than connecting the capillary tube to a remote source of materials for the substrate, the source can be a vial or similar container than can be attached directly to the upper handle  54  of ferrule  50 . 
     In practice, after a substrate has been aligned and secured to the edge compression manifold device, one or more ferrule(s) each with a capillary tube inserted therein is screwed into the appropriate threaded tapered channel of the manifold. As the ferrule is screwed on, the compressive pressure causes the internal bore of the ferrule to collapse against the capillary tube thereby gripping the capillary. Once the ferrules are in place, fluid(s) can be transferred into and/or out of the substrate through the capillaries. 
     FIGS. 7 and 8 also depict the threaded, one piece ferrule. The ferrule includes an adapter body  72  having an hexagonal nut  74  on one side and an elongated member  70 , 78  on the other side. End portion  78  of the elongated member is tapered. The ferrule has internal bore  80 , 82  that runs the length of the ferrule from inlet  88  to outlet  76 . Preferably, as shown in FIG. 8, the proximal portion  82  of the bore is broader to facilitate insertion of a capillary tube into the narrower distal portion  80  of the bore. The wall of the bore at the tapered end will collapse directly against the tube as compressive forces are created as the ferrule is screwed into the threaded conical-shaped cavity. This effectively prevents the capillary tube from extruding during high pressure operations and forms a fluid seal. 
     Each ferrule is machined from a block of material to fabricate a single, integral piece ferrule. The bore is formed using conventional drills and threads are machined preferably on the exterior of the non-taper portion  70  of the elongated member. When using the ferrule, no flange is needed. In addition, a mating sleeve is not needed since the bore will collapse against the tube under compressive force. By “mating sleeve” is meant an extra tube that is inserted into the bore of the ferrule before the capillary tube that will be transferring a fluid of interest is inserted through the bore of the mating sleeve. Mating sleeves having an outer diameter that matches the inner diameter of prior art ferrules are used quite often but are not needed with the inventive ferrule. Machining permits exact tolerance to be maintained to improve fittings function. Because the ferrules are fabricated by machining, that is, they are not made by molding, a wide range of materials, including plastics, ceramics, and metals, for example, can be used depending on the expected operating conditions, e.g., temperature, pressure, and type of fluids the ferrule will be exposed to. The ferrules are reusable and can be finger-tightened to provide a seal that can withstand a minimum pressure of 5,000 psi. 
     The ferrule is suited for all pressure operations typically below 5,000 psi to connect capillary tubes in microfluidic applications and therefore the ferrule is dimensioned accordingly. In this regard, referring to the ferrule shown in FIG. 8, the diameter of the distal portion  80  of the bore is preferably 0.0145 in. (0.368 mm) to 0.015 in. (0.38 mm) and the diameter of the proximal portion  82  of the bore is typically 0.018 in. (0.46 mm) to 0.020 in. (0.51 mm). 
     Preferred capillaries have circular inner diameters that range from 5 microns to 250 microns. Capillaries are available commercially from numerous sources including, for example, Polymicro LLC (Phoenix, Ariz.). The capillary is typically made of glass, metal, silica, or a polymer. 
     Although only preferred embodiments of the invention are specifically disclosed and described above, it will be appreciated that many modifications and variations of the present invention are possible in light of the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.