Abstract:
A reconfigurable modular microfluidic system, providing a microfluidic breadboard platform for the formation of fluidic network and fluidic sealing upon a system assembly. Modular microfluidic elements or “chips” are arranged on a precisely machined alignment base to form a fluidic network, with fluid connections provided directly from chip-to-chip at overlapping corners. Fluidic access to external devices is possible at every fluid connection and through special ingress/egress chips. By maintaining a largely planar layout, optical access is provided for detecting or visualization for every chip. The assembly may be covered by a perforated cover plate.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims an invention which was disclosed in Provisional Application No. 60/470,760, filed May 15, 2003, entitled “RECONFIGURABLE MODULAR MICROFLUIDIC SYSTEM AND METHOD OF FABRICATION”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention pertains to the field of miniaturized chemical and biochemical fluid management systems using microfluidic technology. In particular, the invention relates to the design and fabrication of reconfigurable microfluidic systems using discrete devices and other building blocks on a “breadboard” base.  
           [0004]    2. Description of Related Art  
           [0005]    The concept of the breadboard is well known to those familiar with electronics and electronic circuits. The term “breadboard” derives from the earliest days of electrical experimentation, when circuits were literally built on a base made from a wooden breadboard.  
           [0006]    In the electronics lab, the breadboard system allows an investigator to quickly build a test version of a potentially useful circuit from discrete electronic components. The breadboard framework allows the experimenter to construct a circuit with minimum effort, subsequently enabling the testing of certain values at important locations in the circuit.  
           [0007]    For an electronic circuit, voltage, current and resistance are important factors to be tested. The components are standardized—IC chips, resistors, capacitors, etc., often with a standardized spacing of connections. Once the circuit has been sufficiently tested, a copy can be made in a printed circuit board, or as a mass produced integrated circuit. The breadboard enables one to design and test novel circuits, and sub-circuits, while mitigating the prohibitively expensive process of producing multiple revisions in a mass production environment.  
           [0008]    The breadboard concept is useful in developing integrated microfluidic systems as well. Instead of voltage, current and resistance, the variables governing microfluidic experiments are typically flow rate, pressure, and concentration, but the utility of easily reconfigured systems by the user is the same.  
           [0009]    One of the most attractive features for developing microfluidic systems for life science research is the potential integration of a series of sequential operations on a single device. However, there are inherent difficulties for developing high efficiency, fully integrated microfluidic applications. First, to establish some baseline parameters for the design of an optimized device, sequential operations are preferably developed and characterized in a discrete manner before system integration. This discretization allows the developer to reduce a complex, multi-variable challenge into many smaller, manageable problems and tackle them individually. On the other hand, it is often impossible to test each section of a system in isolation before attempting integration; many components do not provide meaningful information until they are assimilated into the system as a whole. The demand to isolate the specific impact of an individual module in a sequential operation in addition to the ability to investigate the overall performance for the integrated device present an unmet challenge for microfluidic developers.  
           [0010]    A framework for the compilation of modular microfluidic chips, i.e. a “microfluidic breadboard”, would allow the developers to test, alter and retest components in a synchronous fluid management environment which mimics the integrated device without the cost and delay of multiple complete system revisions. However, unlike electronics, there is no standardization of discrete microfluidic components which lend themselves to easy breadboarding, as do the standardized components and packaging of electronic components. Also, the routing of fluids encounters difficulties that are not presented when conducting electrons through wires in electronic circuits.  
           [0011]    In an electronic breadboard, each of the components is supplied with leads that allow it to be wired into the system as a whole. In a fluid management system, tubes or channels must be provided to route the fluid through the system. Fluid leakage, chemical stability of the sealing materials, contamination and cross talk, capillary forces, and void volume must all be considered when designing microfluidic systems. This requires seals made from a material that is chemically compatible with the fluid retained by the system to provide adequate sealing at the required pressure. The seal and design of fluid passage between adjoining devices must prevent the fluid from escaping the intended route; it must do so with a minimum of swept volume in order to maximize the performance of the overall system.  
           [0012]    Currently, the limited options to join discrete microfluidic components to form fluidic network are almost exclusively based on using epoxy with standard capillaries or “Nanoport” fittings made by Upchurch Scientific, a division of Scivex, Oak Harbor, Wash. While the former method is straightforward and widely utilized by many researchers, its cumbersome nature during the capillary and system assembly makes the process very tedious and time consuming. The length of capillary required to make connections increases the overall system length, resulting in higher flow resistances and difficulty when balancing the flow in parallel branches of a system. The complexity of such a capillary network scales up rapidly such that even in the integration of a modest number of microfluidic components, the “plumbing” would become excessively complex. Additionally, the components used in an assembled system are not readily reusable. NanoPort fittings do not suffer from all of the drawbacks of epoxy, but they require precision alignment to the fluid communication port of the microfluidic chip; aligning two 100 μm scale holes via a compressible ferrule is not at all trivial.  
           [0013]    It is also important that optical access into the components of a system be maintained—that is, the individual devices or “chips” must not be obscured from view by the breadboard base or other fittings. Although the fittings that Upchurch Scientific provides are relatively small, in comparison to the chip scale devices to which they attach, they require a bonding area that can exceed the active device area of the fluidic chip. For this reason, there can be difficulties with obscuring the optical access to the active area of the chip. A method is required that allows devices to be easily placed and repositioned while minimizing interval volume as well as assuring optical and fluidic access.  
           [0014]    Purcell&#39;s U.S. Pat. No. 3,548,849, “Fluidic Circuit Package”, discloses means of stacking fluidic components that provides for the synthesis of a microfluidic circuit. However, the stacking of chips, while making the sealing of the components simpler, eliminates the investigator&#39;s ability to monitor the system optically. The stacked scheme also restricts fluid delivery by limiting the available locations for ingress or egress. The purpose of Purcell&#39;s work was to provide a means for producing fluidic circuits in order to replace electronic circuits, not to allow for chemical and biochemical reaction and analysis.  
           [0015]    Bard&#39;s U.S. Pat. No. 5,580,523, “Integrated Chemical Synthesizers” and Hahn&#39;s Published Application no. 2003/0012697 “Assembly Microchip Using Microfluidic Breadboard” disclose means for producing detachable microfluidic systems. In both of these cases, a “motherboard” structure is required to complete the transport of the fluid through the system. This “motherboard” comprises a series of channels in a substrate to which the chips are subsequently connected at predetermined locations. This scheme necessitates adherence to a set base pattern; the flexibility of the system is restricted by the “motherboard” design. The base pattern is predefined and limits the overall microfluidic network configurability.  
           [0016]    Kennedy&#39;s U.S. Pat. No. 6,086,740, “Multiplexed microfluidic devices and systems” and O&#39;Connor&#39;s published application no. 2002/0124896, “Modular microfluidic systems” outline two systems which are created for specific experiments. As in Bard, fluids in these systems are routed from devices through channels in the motherboards.  
         SUMMARY OF THE INVENTION  
         [0017]    The system outlined in this invention uses direct interconnection between modular microfluidic devices (“chips” or “modules”) to form a fluidic network, therefore, there is no rigid predefined fluidic pathways. Fluidic access to external devices is possible at every fluid connection. By maintaining a largely planar layout, optical access is provided for detecting or visualization of every chip. The microfluidic breadboard of the invention is not designed to complete a single, specific, predetermined task—rather, the present invention is designed for reconfigurability to allow testing of a variety of potential microfluidic system designs.  
           [0018]    The microfluidic breadboard described in this invention differentiates itself from the prior art by providing a microfluidic breadboard platform for the formation of fluidic networks and fluidic sealing upon system assembly. In a preferred embodiment the breadboard comprises an array of perforated pockets or wells to hold modules/chips on a precisely machined alignment base. The assembly may be covered by a perforated cover plate. The wells and the modules preferably have a consistent shape.  
           [0019]    The chips may be constructed from a lamination of substrates comprising functional microfluidic features. These features can be accessed through a fluidic communication port or ports on the chip surface, surrounded by a sealing feature. The chips are constructed, and the alignment base is arranged, to provide for overlapping fluid conducting ports in the corners of each chip. Holes in the alignment base then provide a means of egress or ingress of a fluid via connectors and/or provide pressure for sealing at each corner port of every chip location. The chips are designed in three groups: devices that perform specific functions; logic components, and ingress-egress chips that provide means of conducting fluids to desired locations. A complete fluid management system can be constructed by placing the chips into the alignment base in such a way as is desired to carry out the required tasks.  
           [0020]    The base or breadboard is designed and constructed to ensure that when chips are placed into the base plate locating pockets, the fluidic communication ports at each corner of the chip are overlapped to generate a unique application specific fluid network. The leak-free chip-to-chip sealing with minimum void volume is achieved by mating the chip loaded base plate with a perforated cover plate and applying adequate pressure at each corner of the microfluidic chip by using either NanoPort fittings or pre-loaded screws.  
           [0021]    In contrast to the prior art, then, the logic and functional chips of the present invention determine the path of the fluid. They can be juxtaposed to fit any layout required. This gives the present system a level of reconfigurability not provided by a “motherboard” based technology.  
           [0022]    According to this invention, the combination of pre-fabricated pockets for chip alignment, overlapped corner fluid communication port, on-chip sealing means and the flexibility of egress or ingress of a fluid at any fluid communication port provides true chip-level reconfigurability and reusability that is not realized in existing technologies. Upon the completion of or during an investigation, any of the components of the fluid network can be released, replaced or repositioned without disturbing the surrounding components in the system. This arrangement therefore provides the maximum configuration efficiency by keeping the complete assembled fluid network undisrupted during the replacement of the chips and complete network flexibility in that each component of the fluid system can be independently replaced and tested.  
           [0023]    A further embodiment of this invention is that the system provides optical access for fluid visualization or molecular detection on each chip. For any microfluidic application development work, optical access to the fluidic channels is of paramount importance for microscopic or unaided visual inspection, ultraviolet detection or other means. To provide the maximum optical accessibility, the present invention incorporates a perforated cover and base plates to hold microfluidic chips. Each chip preferably includes an optically transparent cover lid. When the chip is positioned in the base plate, the optically transparent side is aligned atop or beneath a viewing window to allow free optical access. This configuration greatly enhances the usability of the breadboard system described herein.  
           [0024]    In order to establish unrestricted fluid ingress or egress at arbitrary fluid communication ports upon system assembly, the present invention provides a means for chip-based fluid connection. In one preferred embodiment, the fluid connection chip is constructed by a particular connecting pattern between the fluid communication ports situated at each corner of the chip to a group of capillaries located in the center. For a chip with four corner fluid communication ports, there are five unique patterns to cover all possible fluid delivery combinations. The five fluid communication chips thus provide a novel modular and reusable fluid ingress or egress method. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 shows an isometric view of chip layout.  
         [0026]    [0026]FIG. 2 a  shows a chip top view.  
         [0027]    [0027]FIG. 2 b  shows a chip cross-section along the line  2   b - 2   b  in FIG. 2 a.    
         [0028]    [0028]FIGS. 3 a  and  3   b  show chip cross section details as indicated by circles  3   a  and  3   b  in FIG. 2 b.    
         [0029]    [0029]FIG. 4 shows sample logic chips.  
         [0030]    [0030]FIG. 5 shows sample fluid ingress/egress chips.  
         [0031]    [0031]FIG. 6 shows sample functional chips.  
         [0032]    [0032]FIG. 7 shows an isometric view of the breadboard system, with base and cover.  
         [0033]    [0033]FIG. 8 shows an isometric view of an alignment base.  
         [0034]    [0034]FIG. 9 shows a top view of the alignment base.  
         [0035]    [0035]FIG. 10 shows an isometric view of the cover.  
         [0036]    [0036]FIG. 11 shows a sectional detail of chip stacking, with the alignment base and cover.  
         [0037]    [0037]FIG. 12 shows a top view of the system of the invention with chips on the alignment base.  
         [0038]    [0038]FIG. 13 shows a detail of the alignment base, in circle  13  in FIG. 9.  
         [0039]    [0039]FIG. 14 shows a detail of the alignment base, in circle  14  in FIG. 9.  
         [0040]    [0040]FIG. 15 shows a section view of the alignment base, along line  15 - 15  in FIG. 9.  
         [0041]    [0041]FIG. 16 shows a section view of the alignment base, along line  16 - 16  in FIG. 9. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0042]    The present invention addresses the need for rapidly building an application specific microfluidic chemical analysis system from standardized components.  
         [0043]    The system of the invention is constructed from a multiplicity of discrete modular microfluidic devices or “chips”, assembled on an alignment base (“breadboard”). The chips are standardized as to shape, size and thickness, allowing great flexibility in assembly of the chips as needed.  
         [0044]    Module/Chip Structure  
         [0045]    In one embodiment of the invention, the chips (microfluidic modules) are essentially square in layout, with a fluid passage or hole (fluid communication port) located at each corner of the chip, surrounded by a sealing feature. The square layout of the chip allows the chips to be arranged in a diagonal array, meaning only one corner of adjacent chips overlap. The diagonal array permitted by this arrangement of square chips and four corner holes gives the ability to branch the fluid path without making special provision in the alignment base. A square chip gives the ability to align the chip in four distinct rotational positions, which is not the case with irregular polygons. Having four positions allows a design which dramatically lessens the number of logic chips needed to maintain flexibility. In other embodiments, the fluid passages are located, alternatively or in addition to locations in the corners, in the center and/or the sides of the microfluidic modules.  
         [0046]    Some other regular polygonal shape could be substituted for the square, including, but not limited to, a triangle, a rectangle, or a hexagon, but with drawbacks. A hexagon can be complicated as far as logic is concerned, and would give rise to problems in manufacture. If a rectangle were used, only two positions would be possible to fit into a prefabricated pocket. Circular chips could be employed, but would be less space efficient and would present alignment difficulties. The same considerations apply for using only four holes. If eight were used, for example, the logic would be more difficult to manage. These factors argue in favor of square chips with four corner ports to allow the building of highly complex systems with a very limited number of chip variations.  
         [0047]    All of the chips are positioned relative to each other in an alignment base. The alignment base assures that the fluid communication ports on each of the chips align with those of the adjacent chips, so that fluid can flow directly between the chips without leakage and without unnecessary interconnecting tubing, voids or volumes. The alignment base and chips are then preferably secured via a cover.  
         [0048]    [0048]FIG. 1 shows an isometric view of a fluidic chip  10  which can be used with the invention. The chip is constructed from two or more layers  11 ,  12 . These layers can be made of a variety of materials such as silicon, glass or plastic. Layer  12  is patterned with the chosen fluid passageways or specific features (“microfluidic architecture”). Ports  13  are provided normal to the substrate surface connecting to the microfluidic architecture. Sealing means  14  are provided to seal between chips and to external connectors.  
         [0049]    The seals  14  can be made from any of a group of polymers exhibiting the required elasticity and chemical resistance, for example, silicone, fluoropolymer, fluorosilicone, latex, or polyamide. The material may be patterned by photolithography, screen-printing, lamination, cut sheet, injection molding or direct deposition, these being suitable processes for wafer level parallel processing.  
         [0050]    [0050]FIG. 2 a  shows the top of a fluidic chip  10 , in this case a logic chip of the “cross” type shown at  47  in FIG. 4. FIG. 2 b  shows a cross section of the chip, along line  2   b - 2   b  in FIG. 2 a . FIG. 3 shows details of the cross sectional view of the chip, as indicated by circles  3   a  and  3   b  in FIG. 2 b.    
         [0051]    The microfluidic channel  15  of the logic chip can be seen patterned in the surface of substrate  12 . This pattern may be created by means of etching in silicon, specifically Deep Reactive Ion Etching (DRIE), by machining or by wet chemical etching. Similar means may be useful for patterning glass substrates. In the case of plastics, injection molding, embossing, casting, or machining may be suitable.  
         [0052]    The ports  13  may be created by DRIE, laser, or ultrasonic machining in silicon; laser, wet chemical etching or ultrasonic machining in glass; and laser or standard machining, or as part of the injection molding process in plastic. Any of the two or more substrates,  11  and  12 , may have ports  13  provided allowing fluid to pass from either side of the chip to architecture  15  at the interface  16 ; or to pass completely through the chip; or a port or ports can be left out to provide a stoppage. In the example shown, the port  13  is only in substrate  12 , and is blocked off at substrate  11 .  
         [0053]    The two substrates,  11  and  12 , are then sealed together to form an enclosed microfluidic structure. This interface  16  can be sealed by any suitable means—anodic or fusion bonding for glass/silicon, silicon/silicon and glass/glass substrates; adhesive bonds for glass, plastic, or silicon combinations; and direct lamination for plastic substrate stacks.  
         [0054]    The chip sealing pads  14  are provided on both surfaces  17  and  18  of the chip. The seals provide sealing between chips when placed face to face, or seal against the cover or the alignment base, to be discussed below.  
         [0055]    Types of Chips  
         [0056]    The chips are grouped into three categories: those that serve to direct the fluid flow are called “logic chips”, those which provide inlets and outlets are called “ingress/egress chips” and those that perform a specific chemical or biological or other function are called “functional chips”.  
         [0057]    [0057]FIG. 4 shows various types of logic chips, which can be used with the invention. The purpose of the logic chips, as mentioned above, is to route the fluid to the desired locations through a specific layout. Each of the chips has at least one corner port  13 , although in some variations the ports are not connected to any channels within the chip. In FIG. 4, the chips each have four corner ports  13 . Eight combinations of connections between the ports in FIG. 4 are shown. Each of the logic chips is preferably designed to be an equal path length from port to port to assure pressure balanced, predictable flow.  
         [0058]    Chip  41  is the equivalent of a “T” connection. Preferably, as shown, the channels are structured to maintain no preferential flow by intersecting at 120-degree angles.  
         [0059]    Chip  42  is simply a blank chip that could provide a “plug” or be used as a spacer in the system. The corner ports  13  could be through holes, or plugged, as desired.  
         [0060]    Chip  43  is a “cross over”, allowing fluid to pass diagonally between opposite corners in two separate paths  80  and  81  without intermixing. This chip would require a three-layer construction. The middle layer would contain a channel defined on each of its faces, with the appropriate corners ported through the lid or both the lid and middle substrate respectively, to form the two fluid paths.  
         [0061]    Chip  44  is an inline connection, as is chip  45  with the exception that  45  contains two channels in parallel. By rotating chip  44  into each of its four possible orientations, paths between adjoining chips can be established. Similarly, chip  45  can be rotated into two positions, so that adjoining chips horizontally or vertically can be connected.  
         [0062]    Chip  46  is an inline connection from corner to corner, this being the single channel version of chip  43 .  
         [0063]    Chip  47  is a commonly referred to as a “cross”—the arrangement of channels is the same as in chip  43 , but on only one layer, so that all of the ports  13  are connected together.  
         [0064]    The logic chips described above are all passive conduits, but it is possible within the teachings of the invention to have logic chips which allow control of fluid flow. As examples, chip  48  is a fluidic switch, in which flow from channel  82  may be switched to channels  83  or  84  by pressure in channel  85  (or, in the inverse, flow from channels  83  or  84  might be selected to flow into channel  82 ) and chip  49  shows a logic chip which has a one-way (“check”) valve  87  in channel  86 .  
         [0065]    Other active and passive logic chip designs are possible within the teachings of the invention.  
         [0066]    [0066]FIG. 5 shows various examples of fluid ingress/egress chips. Each of the fluid ingress/egress chips provide access to the ports  13  directly from a capillary tube  56 . The capillary tube  56  is preferably a fused silica drawn tube with a polyamide coating. Its outside dimensions are preferably between 50 and 700 μm. This tube would be inserted and fixed into a hole located through the lid of the chip. This hole would provide fluid passage from the capillary to the channel  57  as well as alignment and anchorage for the capillary  56 .  
         [0067]    The various chips shown in FIG. 5 are the preferred embodiments. Each of these variations allow for connections to any or all of the fluid access points in the fluid layout. For example, chip  51  could connect to any individual corner port (simple by rotating in quarter turn increments), while chip  55  would connect to all of the corners. Chips  52  and  53  have two connections, vertical/horizontal or diagonal, respectively, and chip  54  has three connections with the fourth blanked off. It will be understood that other ingress/egress chip designs would be possible within the teachings of the invention, and that the ingress/egress design could be combined with one of the logic chip designs if desired.  
         [0068]    [0068]FIG. 6 shows several possible functional chips which could be used with the invention. These sample chips are a mixer  61 , a liquid chromatography column  62 , a flow cell for use with a UV spectrometer  63 , and a liquid extraction column  64 . Other functional chips could be used within the teachings of the invention, such as micropumps, heaters, electrospray or electrophoresis apparatus, reservoirs or reactors, or sensors of various kinds such as pressure, flow, conductivity, temperature or density.  
         [0069]    The Alignment Base and Cover Assemblies  
         [0070]    [0070]FIGS. 7 and 8 show isometric views of the alignment base  70  for use with the system of the invention. In FIG. 7, the cover plate  71  is shown hinged to the base. FIG. 9 shows a top view of the alignment base, with details shown in FIGS. 13 and 14, and cross section views in FIGS. 15 and 16.  
         [0071]    Referring to FIGS. 7 and 8, the alignment base has an orthogonal arrangement of rows and columns of wells  72  into which the chips are placed. As can be seen in FIG. 9, the rows and columns of wells can be designated by letters or numbers for ease of reference. In this explanation, the locations on the base will be denoted by letters for rows and numbers for columns, such that location E 1  is the fifth row from the top, first column from the left.  
         [0072]    While the figures show the wells in eleven columns and seven rows in a rectangular base, it will be recognized that other arrangements are possible, depending on the base shape desired. For example, both the base and the wells could be in a square shape, or the base could be round with the rows and columns of wells arranged to fill. A linear arrangement is possible as well as, for example, three rows and ten or more columns.  
         [0073]    In FIGS. 7 and 8, optical access holes are shown at  78  in the base and  73  and  77  in the cover—it will be noted that FIGS. 7 and 8 show these holes in the odd-numbered columns in the base and the even-numbered columns in the cover, but in a preferred embodiment all of the wells are provided with optical access holes, both in the base and the cover. Although not shown, in one embodiment, the cover plate provides fluid access holes to the fluid communication ports in the microfluidic modules.  
         [0074]    Holes  75  and  76  in the base and  74  in the cover allow base and cover to be tightened together by screws, if desired.  
         [0075]    Referring to FIGS. 9 and 13- 16 , it can be seen that the wells are of two kinds, deep and shallow. The deep wells  91  are in the five even-numbered columns, the shallow wells  90  in the six odd-numbered columns. The wells are positioned so that the corners of the wells in adjacent columns overlap, allowing chips to overlap on their corners  94 . The chips in the deep wells  91  are thus positioned so that their corner ports  13  (FIGS. 1-3) are precisely aligned underneath the corner ports  13  of the chips in the shallow wells  90 .  
         [0076]    Each corner of each well  90  and  91  is preferably provided with a threaded through-hole  93 , which extends from the well completely through the base  70 . This allows insertion of fluidic connectors or screws from underneath the base  70 , as will be seen in the discussion of FIG. 11, below.  
         [0077]    In the figure shown, the wells  90  and  91  have optical windows or holes for optical or other access from underneath the chips.  
         [0078]    [0078]FIG. 12 shows a base plate  70  in which two complete microfluidic “circuits”  610  and  620  are assembled.  
         [0079]    For ease of reference in this figure, functional chips have been assigned “300” series reference numbers, logic chips are in the “400” series, and ingress/egress chips have “500” numbers. Fluid circuits or flows are “600” series numbers. The second digit of the reference number is the fluidic circuit number, so that chip  310  would be a functional chip in the first microfluidic circuit, chip  522  an ingress/egress chip in the second circuit.  
         [0080]    The first system is a liquid chromatography separation arrangement. It consists of three functional chips, three logic chips and three ingress/egress chips.  
         [0081]    The setup begins in wells E 1  and C 3  with two fluid ingress lines  611  and  612 , leading to chips  511  and  512 , both single-capillary ingress/egress chips of the type shown at  51  in FIG. 5.  
         [0082]    A mixer  310  is located in deep well D 2 , which puts two of its corner ports underneath the corner ports of ingress/egress chips  511  and  512 . The mixer  310  mixes flows  611  and  612 , and the output of the mixer  310  goes to the corner port which overlaps the corner port of liquid chromatography column chip  311  in well E 3 . In turn, the output port of chip  311  overlaps the input of UV detection flow cell chip  312 .  
         [0083]    Finally, the flow  613  exits from one of the capillaries of fluid egress chip  513 . As can be seen, chip  513  is a four-capillary chip as shown at  55  in FIG. 5, but only two of the ports are used—one for this circuit, one for outflow  623  of circuit  620 . This illustrates the flexibility of the system, as one chip can be used for more than one circuit, and the unused ports merely communicate with corners of the well without introducing any unwanted voids or leakages into the circuits.  
         [0084]    The second circuit  620  is a parallel liquid/liquid extraction configuration.  
         [0085]    Two immiscible fluids  621  and  622  are introduced into the two capillaries of ingress/egress chip  521  in well B 8 . This chip overlaps with logic chips  421  and  422  in wells C 7  and C 9 , respectively, which are divider chips of the sort shown at  41  in FIG. 4. The chips  421  and  422  divide the fluids  621  and  622 , and half of each is supplied to an input of non-contact cross over logic chip  423  in D 8 , which is the kind shown at  43  in FIG. 4. The other half of each flow is routed from chips  421  and  422  to inline connection chips  424  and  425 , respectively. Chips  424  and  425  are of the kind shown at  44  in FIG. 4. As can be seen, the chips have been rotated 180° with respect to each other, allowing the same type of chip to be used in both locations, routing fluid through different sets of ports.  
         [0086]    The four flows then proceed into two liquid extraction chips  321  in well E 7  and  322  in E 9 . Chip  321  is fed from chip  424  by half of flow  621 , and from one of the paths in chip  423  by half of flow  622 . Similarly, chip  322  is fed from chip  425  by half of flow  622 , and from the other path in chip  423  by half of flow  621 .  
         [0087]    The output flow from chip  321  is routed into flow cell  323 , and then exits as flow  623  through one capillary of ingress/egress chip  513 . The output flow from chip  322  is routed into flow cell  324 , and is collected through a Nanoport fitting  625  threaded through the bottom of the base  70 , to exit as flow  624 . A blanked or spacer chip  325 , of the kind shown at  42  in FIG. 4, provides the proper spacing and prevents leakage  
         [0088]    The two remaining flows are collected through an egress chip  522  without detection, and exit as flows  626  and  627 .  
         [0089]    From above description, it becomes apparent to those skilled in the field to realize that many different configurations with a wide range of devices on the breadboard can be achieved.  
         [0090]    For example, micromachined pumps, valves and different types of sensors can be placed at the appropriate location to deliver fluid, control the flow direction and detecting molecular or electronic signals. A UV flow cell  330  can be replaced or followed by a chip with shallow channels for using a Laser Scanning Confocal Microscopy (LSCM, also referred to as CSLM, Confocal Scanning Laser Microscopy) for obtaining high resolution images and 3-D reconstructions of a variety of biological specimens.  
         [0091]    Once the chips are in place, the cover  71 , shown in FIGS. 7 and 10 is then secured to the alignment base  70  by screws through holes  74  and  75 . When the fluidic connectors or screws are tightened from the back of the alignment base in the threaded holes  93 , the devices are forced together and seal to one another and the fluidic connections and the cover.  
         [0092]    [0092]FIG. 11 shows a detail of three chips  170 ,  171  and  172 , assembled into the base  70  and with the cover  71  in place. As can be seen in the figure, chips  170  and  172  are in shallow wells  90 , and chip  171  is in deep well  91 .  
         [0093]    Optical holes  92  allow access to the bottom of chip  171 , and holes  73  allow access to the tops of chips  170  and  172 , respectively. The objective of a microscope  185  is shown inspecting the fluid flow in chip  171  through the central cover hole  73 . The chip is illuminated from underneath by light  186  directed through access hole  92  in the base.  
         [0094]    Through-holes  93  can be seen in the base  70 , with spring-loaded screws  178  in three of the holes. The spring-loaded screws apply a force to press the seals  177  of the chips against the cover  71 , and also seal the bottom of the corner ports in the chip. The outlet port of chip  172  is routed through the back of the alignment base  70  using a threaded fitting  176 . When the threaded fitting is tightened, it applies a force to seal the chip  172  against the cover, and also provides a route for fluid through the hollow center.  
         [0095]    The fluid flowing through the example of FIG. 17 is shown as dashed line  175 . It enters through a capillary fitting  174  in chip  170 , then goes through a channel in the chip to corner port  179  and into corner port  180  in chip  171 . The fluid then flows through chip  171  and out through corner port  181  into corner port  182  in chip  172 . After flowing through chip  172 , the flow leaves through corner port  183  into fitting  176  and out the bottom of the base  70 .  
         [0096]    Fabrication of the Invention  
         [0097]    It is preferred that fluid devices described according to the present invention be fabricated using fabrication methods and equipment developed for the creation of microelectromechanical (MEMS) devices.  
         [0098]    Dry etching of silicon, whether primarily physical in nature (ion-milling) or primarily chemical (plasma etching), is a highly evolved part of the overall fabrication process. Particularly preferred is Reactive-Ion Etching (RIE) or Deep Reactive Ion Etching (DRIE) techniques.  
         [0099]    These techniques employ a combination of physical and chemical mechanisms, and are the most commonly practiced embodiment of dry etching. A particular class of silicon etch processes has been developed specifically for high-aspect-ratio etching of silicon in MEMS applications. See U.S. Pat. Nos. 4,784,720 and 4,855,017 (Lärmer et al.), for explicit descriptions of these specialized etch processes, collectively known as the “Bosch” process or Deep Reactive Ion Etching (DRIE).  
         [0100]    The advantages of using DRIE process is its ability to produce very fine features, sizes on the order of 1 um. As the process is very anisotropic, meaning the etch is strongly preferential to a particular direction, the mask is very closely reproduced in the substrate. This is not the case for most RIE processes. Very often an RIE etch process will produce an undercut of the mask, limiting the control over fine feature sizes. Additionally, the lack of anisotropy in RIE etches limits the aspect ratio of the features being etched to near 1:1. With DRIE, one can obtain aspect ratios of 50:1, 1:50 or beyond.  
         [0101]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.