HK1084067B - Microfluidic apparatus with integrated porous-substrates/sensor for real-time(bio) chemical molecule detection - Google Patents

Description

Microfluidic device with integrated porous substrate/sensor for real-time biochemical molecular detection

Technical Field

The present invention relates generally to microfluidic devices, and more particularly, but not by way of limitation, to microfluidic devices having porous membranes with integrated sensors for filtering and detecting biological and/or chemical molecules.

Background

As the range of microchip manufacturing technologies continues to expand, a new technology has emerged in connection with micro-scale features known as microfluidic devices. Through continued development, microfluidic devices have been available in a variety of contexts, the devices typically including miniaturized reservoirs, pumps, valves, filters, stirrers, reaction chambers, and capillary networks connecting the subcomponents. For example, microfluidic devices can be designed to perform hundreds of operations (e.g., mixing, heating, separation) without human intervention to perform several reactions and analyses in one micro-instrument. In some cases, the microfluidic device may act as an air toxin detector; a rapid DNA analyzer for crime investigators; and/or a novel drug test to accelerate drug development.

In recent years, researchers have found that porous substrates, such as nanocrystalline silicon, can be fabricated to examine specific biochemical structures. For example, researchers have developed porous substrates that can be used to detect parts per billion (ppb) TNT and dinitrotoluene (see http:// chem-failure. ucsd. edu/sailor).

While the applications of such microfluidic devices and sensing substrates are virtually unlimited, the integration of portions of the microassembly into a microfluidic system is technically difficult, thus limiting the range of functions that can be performed by a single device or a combination of devices. In particular, current microfluidic systems do not adequately integrate a size-separating (or filtering) filter into a microfluidic chip. Therefore, separation operations must often be performed in an externally packed porous media or polymer-based nanopore (nanopore) membrane, increasing the risk of contamination when performing assays or other techniques, and adding additional complexity and human intervention. Furthermore, the sensing substrate is not integrated into a chip or similar element.

Disclosure of Invention

In one aspect, the present invention provides an apparatus comprising: a substrate having defined therein: an upper microfluidic channel through the substrate in a first direction; a lower microfluidic channel through said substrate in a second direction, a portion of said lower microfluidic channel passing below a portion of said upper microfluidic channel to form a cross-channel region; and a porous membrane positioned between the upper microfluidic channel and the lower microfluidic channel and adjacent to the crossover channel region to form a semi-permeable barrier between the upper microfluidic channel and the lower microfluidic channel.

Further, the porous membrane has a medium thickness ranging from 10 nanometers to 50 nanometers.

In another aspect, the present invention also provides an apparatus comprising: a substrate having defined therein: a plurality of upper microfluidic channels through the substrate in a first direction; at least one lower microfluidic channel through the substrate in a second direction, a respective portion of the at least one lower microfluidic channel passing under a respective portion of the upper microfluidic channel to form a plurality of respective cross-channel regions; and at least one porous membrane positioned between the upper microfluidic channel and the lower microfluidic channel and adjacent to the cross-channel region to form a semi-permeable barrier between the upper microfluidic channel and the lower microfluidic channel in a corresponding region adjacent to the plurality of cross-channel regions.

In addition, the present invention also provides an apparatus comprising: a substrate having defined therein: a plurality of upper microfluidic channels formed in said substrate, each upper microfluidic channel having a first end and a second end, said second ends converging at an intersection; a lower microfluidic channel formed in said substrate having a first end located below said intersection; and a porous membrane positioned between the upper microfluidic channel and the lower microfluidic channel and proximate to the intersection point to form a semi-permeable barrier between the upper microfluidic channel and the lower microfluidic channel.

Drawings

In the drawings, wherein like reference numerals represent like parts throughout the several views of non-limiting, non-exclusive embodiments of the present invention, and wherein:

FIGS. 1 a-1 f are various views of a microfluidic device according to an embodiment of the present invention, wherein FIGS. 1a and 1b are exploded perspective views, FIG. 1c is a sectional view corresponding to cut lines 1c-1c, FIG. 1d is a broken line isometric view, FIG. 1e is an isometric view containing a composite section, and FIG. 1f is a top view containing cut lines 1c-1 c;

FIGS. 2 a-2 e are various views of a microfluidic device according to an embodiment of the present invention, wherein FIGS. 2a and 2b are exploded perspective views, FIG. 2c is a phantom line isometric view, FIG. 2d is a top view including cut lines 2e-2e, and FIG. 2e is a cross-sectional view corresponding to cut lines 2e-2 e;

FIGS. 3 a-3 e are various views of a microfluidic device according to an embodiment of the present invention, which is a variation of the embodiment shown in FIGS. 2 a-2 e, wherein FIGS. 3a and 3b are perspective exploded views, FIG. 3c is an isometric broken line view, FIG. 3d is a top view including cut lines 3e-3e, and FIG. 3e is a cross-sectional view corresponding to cut lines 3e-3 e;

FIGS. 4 a-5 e are various views of a microfluidic device according to embodiments of the present invention, in which a porous substrate/sensor array is employed, wherein FIG. 4a is an exploded perspective view, FIG. 4b is an isometric assembly view, FIG. 4c is a top view including cut lines 4d-4d and 4e-4e, and FIG. 4d is a cross-sectional view corresponding to cut lines 4d-4 d; and FIG. 4e is a cross-sectional view corresponding to tangent line 4e-4 e;

FIGS. 5 a-5 e are various views of a microfluidic device according to an embodiment of the present invention, which is a variation of the embodiment shown in FIGS. 4 a-4 e, wherein a single porous substrate/sensor is employed, wherein FIG. 5a is an exploded perspective view, FIG. 5b is an isometric assembly view, FIG. 5c is a top view including cut lines 5d-5d and 5e-5e, and FIG. 5d is a cross-sectional view corresponding to cut lines 5d-5 d; and FIG. 5e is a cross-sectional view corresponding to cut line 5e-5 e;

FIGS. 6 a-6 e are various views of a microfluidic device according to an embodiment of the present invention, in which a plurality of upper channels meet at an intersection, where FIGS. 6a and 6b are perspective exploded views, FIG. 6c is an isometric broken line view, and FIG. 6d is a top view including cut lines 6e-6 e; and figure 6e is a cross-sectional view corresponding to cut line 6e-6 e;

FIG. 7a is a flow chart of manufacturing a porous membrane according to an embodiment of the present invention;

FIG. 7b is a flow chart of manufacturing a porous membrane according to another embodiment of the present invention;

FIGS. 8 a-8 c are various views of an optical sensing device for detecting changes in optical properties of a porous membrane/sensor corresponding to the embodiment of FIGS. 1 a-1 f, wherein the internal volume of the substrate is shown;

FIGS. 9 a-9 c are various views of an optical sensing device for detecting changes in optical properties of a porous membrane/sensor corresponding to the embodiment of FIGS. 4 a-4 e, showing the internal volume of the substrate; and

FIG. 10 is a schematic diagram of one embodiment of the present invention for detecting a change in an electrical characteristic of a porous membrane/substrate.

Detailed Description

Detailed herein are embodiments of a microfluidic device with integrated porous-silicon (pore-silicon) thin films for molecular screening, metering, and separation, and methods for making and using the microfluidic device. In the following description, numerous specific details are provided, such as identification of various system components, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

In view of the foregoing, embodiments of the present invention provide a microfluidic device having at least one integrated porous silicon membrane for screening, metering, and/or separating molecular components from a fluid stream introduced into the microfluidic device. Other features of the described embodiments will be apparent from the foregoing description and appended claims, taken in conjunction with the accompanying drawings, wherein like reference characters refer to like parts throughout.

Shown in fig. 1 a-1 f is a microfluidic device 100 according to one embodiment of the present invention. The microfluidic device 100 includes a platform substrate 102 in which an upper microfluidic channel 104 and a lower microfluidic channel 106 are formed. The upper and lower microfluidic channels are oriented such that the upper channel spans the lower channel at a "cross-channel" region 108. A porous substrate 110 is located between the upper and lower channels near this cross channel region. As will be described in further detail below, the porous substrate 110 includes a plurality of pores through which molecules of a portion of the fluid (e.g., liquid and gas) can pass, but through which other molecules cannot pass.

In various embodiments, a reservoir may be connected to one or both ends of the upper channel and/or the lower channel. For example, in the illustrated embodiment, input and output reservoirs 112 and 114 are connected to the input and output ends of the upper channel 104, respectively, while input and output reservoirs 116 and 118 are connected to the input and output ends of the lower channel 106, respectively. Generally, it is desirable that the liquid flow through each of the upper and lower channels be in a particular direction. In view of this, in one embodiment, the depth of the output reservoir extends below the depth of the channel. Thus, when liquid is added to the input reservoir, it flows through the channel to the output reservoir. Instead of or in addition to the output reservoir, respective outlet paths (not shown) for the upper and lower channels may also be provided.

Typically, the platform substrate comprises upper and lower halves that are sandwiched around one or more porous membranes/sensors. For example, as shown in fig. 1E and 1F, the platform substrate includes an upper substrate member 120 and a lower substrate member 122. As shown in fig. 1F, the upper microfluidic channel 104 is located in the upper substrate component and the lower microfluidic channel 106 is located in the lower substrate. In one embodiment, the input and output reservoirs 116 and 118 and the lower portions 116B, 118B and 114B of the output reservoir 114 are located in the lower substrate member, respectively, while the corresponding through holes 112A, 114A, 116A, 118A are located in the upper substrate member. Generally, the upper substrate component and the lower substrate component are sandwiched around the porous membrane 110 when assembled. Thus, a recess is formed in the upper substrate member or the lower substrate member for receiving the porous membrane when assembled. For example, in the illustrated embodiment, a recess 124 is defined in the upper substrate component 120.

Fig. 2 a-2 e show an embodiment of a single "flow-through" microfluidic device 200. In one implementation, the first reactant fluid flows into the input reservoir 212 and into the upper channel 204. At the same time, the second reactant fluid flows into the input/output reservoir 214 and into the lower channel 206. A portion of the first and second reactants then flow through the pores of the porous membrane 210 and mix to produce a reaction. In a manner similar to that described above, the porous membrane may change optical or electrical properties in response to a particular chemical reaction, such that the chemical reaction is detected.

In another implementation of the embodiment shown in fig. 2 a-2 e, a single fluid is input to the input reservoir 212 and flows into the upper channel 204. The portion of the fluid then passes through the porous membrane 210 and into the channel 206. A portion of the fluid flowing through the porous membrane may then be collected in the input/output reservoir 214. In this embodiment, the fluid causes a change in the optical and/or electrical properties of the porous membrane in a manner similar to that described above.

In one embodiment, microfluidic device 200 comprises a three-piece assembly including an upper substrate member 220 and a lower substrate member 222, both of which are sandwiched around porous membrane 210. As previously described, a recess may be formed in the upper substrate member or the lower substrate member to receive the porous membrane, such as defining a recess 224 in the upper substrate member 220.

Fig. 3 a-3 e illustrate a microfluidic device 200A that is substantially similar in structure to microfluidic device 200. The main difference between the two devices is that the microfluidic device 200A includes an outlet port 230 instead of an input/output reservoir 214. Modifications containing this variation have been shown in upper substrate component 220A and lower substrate component 222A.

Fig. 4 a-4 e show a microfluidic device 300 according to another embodiment of the present invention. The microfluidic device 300 has a plurality of upper channels 304A, 304B, 304C formed in an upper substrate component 320 and a plurality of lower channels 306A, 306B, 306C formed in a lower substrate component 322. Optionally, a plurality of input reservoirs 312n (a-c) and 316n, and output reservoirs 314n and 318n may also be provided. In one embodiment, a plurality of porous membranes 310 are disposed in corresponding recesses (not shown) in the upper substrate member 320 in a manner similar to that described above. In another embodiment, a single porous membrane 310A may be used, as shown in microfluidic device 500A in FIGS. 5 a-5 e. Alternatively, the single porous membrane may be fabricated to contain multiple porous segments, such as square or rectangular segments (not shown) arranged in an array.

Fig. 6 a-6 e show a microfluidic device 600 according to another embodiment of the present invention. The apparatus includes an upper substrate member 620 in which three upper channels 604A, 604B, 604C are formed. Alternatively, an input reservoir 112 may be placed at the input end of each channel 604A-604C, with the output ends of the channels meeting at intersection point 611. The device further includes a lower substrate member 622 in which the single lower microfluidic channel 606 is formed, wherein the lower substrate is similar in structure to the lower substrate member 164 of the microfluidic device 150. An output reservoir 616 may also be provided to collect fluid that is to exit the lower microfluidic channel. The device further includes a porous membrane 610 positioned within a recess 624 in the top substrate component 620, wherein the recess is positioned proximate to the intersection point 611.

The microfluidic device 600 may generally be used in the following manner. Respective fluidic reactants may be received (e.g., via input reservoirs 612A-612C) at the input of the upper microfluidic channel 604. The fluid reactants may then mix at intersection point 611, which may cause a chemical reaction. A portion of the generated reactive compounds will flow into the pores of the porous membrane 610, causing a potential change in the optical and/or electrical properties of the porous membrane. This change in characteristic can be measured in the manner described below.

Porous film fabrication and features

According to one aspect, the porous membrane comprises a porous structure that can be used for filtering, metering, and/or separating chemical and/or biological molecules. In general, porous membranes can be fabricated to have the greatest porosity in a selected direction. Moreover, the pore size can be adjusted from a few nanometers to a few micrometers throughout the manufacturing process described below, thereby enabling the filtration, metering, and separation of target biochemical molecules.

In general, the porous membranes and porous membranes/sensors can be fabricated from a variety of materials that can form nano-and micro-porous structures. For example, such materials include, but are not limited to, single crystal Porous Silicon (PSi), Porous Polycrystalline Silicon (PPSi), porous silica, zeolites, photoresists, porous crystals/polymers, and the like. Typically, the porous membranes are used in molecular separation and/or molecular (bio) reaction media for internal real-time detection/monitoring of processes, molecules, fluids, reaction conditions, etc.

In one embodiment, porous silicon is used as the porous membrane. Porous silicon enables a superior material to be prepared by electrostatic, chemical, or photochemical etching processes in the presence of HF (hydrofluoric acid) (a.g. cullis et al, appl.phys.1997, 82, 909). Porous silicon can be fabricated into complex, anisotropic nanocrystalline structures (see http:// chem-factty. ucsd. edu/sailor) typically using electrochemical etching or dye etching in the silicon layer. The size and orientation of the Pores can be controlled by the etching conditions (e.g., current density, etc.), the type of substrate and its electrochemical Properties (R.L. Smith, et al, "ports silicon Formation mechanisms", J.appl.Phys., 1992, 71, R1; P.M. Fauchet, "pins and ports: Formation, Properties, and Significence for Advanced luminescence Materials", P.Schmuki, et al, eds. Pennington, N.J. electro-chemical. Soc., 1997, 27). Typical pore sizes range from about 50 angstroms to about 10 microns, with pores in silicon having extremely high aspect ratios (about 250) extending over distances of several millimeters.

Another porous silicon can be made by spark erosion (r.e. hummel, et al, "On the orientation of phosphors in spark-ignited (porous) silicon", appl.phys.lett., 1993, 63, 2771), resulting in a textured Si surface of various sizes from micron to nanometer. Si nanostructures can be prepared using anisotropic etching after oxidation (a.g. nanoslouos, et al, "Light emission for silicon nanostructure by systematic concerned and reactive etching", physics.stat.sol (B), 1995, 1990, 91; s.h. zaidi, et al, "Scalable surface optical characterization of nm Si structures", In proc.sym.mater.soc, 1995, 358, 957). By oxidizing the microcrystalline film deposited by chemical vapor deposition, the Si crystals are passivated with SiO to form a nanocrystalline structure (H.Tamura, et al, "Origin of the green/blue luminescence from nanocrystalline silicon", applied.Phys.Lett., 1994, 65, 92).

Referring to the flow chart of fig. 7a, a process of manufacturing a porous membrane (e.g., 110, 310, etc.) according to one embodiment of the invention is as follows. First, in block 700, porous silicon may be etched by electrochemical or dye etching in a silicon layer having a standard thickness of about 0.01-50 microns to form porous silicon. In another embodiment, as shown in block 702, Porous Polysilicon (PPSi) may be deposited by Low Pressure Chemical Vapor Deposition (LPCVD). The size and orientation of the pores, porosity, grain size, thickness, etc. can be controlled by appropriate etching conditions (e.g., current density, current duration, etc.), deposition conditions (e.g., temperature, pressure, etc.), and the type of substrate and its electrochemical properties.

Next, in block 704, the PSi film (or PPSi film) may be physically separated by electropolishing, stripped from the PSi-etched silicon or PPSi-deposited silicon, and suspended in solution. Alternatively, the PPSi film may be formed when deposited directly on a substrate (e.g., silicon, quartz, etc.) and may be physically separated using any of a variety of standard etching or micromachining techniques. The PSi or PPSi film is then secured in a corresponding recess in the substrate half proximate the crossover channel region in block 706.

In an alternative process shown in FIG. 7b, PPSi is deposited directly on the substrate cavity using LPCVD at block 708 to form the porous membrane. Subsequently, in block 710, a via is etched in the substrate, a portion of which passes under the deposited PPSi. In general, the substrate may comprise any suitable material in which the microfluidic channel may be formed (e.g., silicon, quartz, Polydimethylsiloxane (PDMS), SU-8 photoresist), as well as polymers (e.g., Polymethylmethacrylate (PMMA), etc.).

Real-time detection of biological and chemical molecules/compounds

As described above, in various embodiments, the porous membrane may also be fabricated such that it can function as a sensor in addition to a filtering/screening/molecular separation function. For example, the porous membrane may be fabricated such that it undergoes a change in optical and/or electrical properties in response to being exposed to a target fluid or reactant, by utilizing the base substrate material (e.g., PSi or PPSi) or by adding a sensing layer or by chemical doping and the like. In general, such PSi or PPSi sensor mechanisms may include, but are not limited to, optical interferometric reflection, capacitive modulation, photoluminescence, optical form birefringence, acoustic, and the like.

In one embodiment, as shown in FIGS. 8 a-8 c and 9 a-9 c, optical variations can be observed using a light source 800 and an optical detector 802 (note that in these figures, only the volume occupied by the reactant fluid, also referred to as solute and analyte, is shown for clarity. In general, light source 800 may comprise any device capable of generating light suitable for detection, which may cooperate with a corresponding optical detection apparatus or device to detect changes in the optical characteristics of the porous membrane/sensor. For example, in one embodiment, light source 800 comprises a laser light source that generates light at a particular wavelength.

Depending on the specific optical properties of the porous membrane/sensor, visible or invisible light may be used. In terms of visible light wavelengths, in one embodiment, at least one of the upper and lower substrates is transparent, which means that the substrate(s) produce the lowest attenuation of visible light. In some instances, one may wish to use light having wavelengths in the invisible spectrum (infrared), if present. Many substrate materials are "semi-transparent" to these wavelengths, meaning that the materials are transparent to light having certain invisible wavelengths with minimal attenuation. Alternatively, various viewing aperture structures are defined in a substrate that is opaque to light of a wavelength used to detect changes in the optical properties of the porous membrane (not shown).

In general, various optical detectors may be employed depending on the particular optical characteristics to be observed. In one embodiment, the optical detector comprises a detector adapted for a laser interferometer. Other standard optical detectors include, but are not limited to, avalanche photodiodes, various light sensors, and other devices that can be used to measure wavelength, phase shift, and/or light energy/power.

The optical detector typically also includes an internal data recording device, or an external data recording device (e.g., data recorder 804) connected to the optical detector. Alternatively, a computer 806 equipped with a data logging card or electronic instrument interface (e.g., a GPIB (general purpose instrument bus) interface) may be used. The data logger may store data on a local or computer network, for example, in a data store controlled by a database or data system or a Storage Area Network (SAN) device.

For changes in electrical characteristics, various electronics and/or circuitry may be electrically coupled to the porous membrane to detect the changed condition. As described above, this can be accomplished using a microelectronic circuit (e.g., microelectronic circuit 1000 in fig. 10) disposed in the substrate. Alternatively, the substrate may be directly connected to external circuitry and/or electrical devices by wire bonding and the like. In one embodiment, signal conditioning and/or test measurement circuitry may be fabricated directly in the platform substrate, as is common in semiconductor fabrication techniques, as shown by integrated circuit 1002. Optionally, this signal conditioning and test measurement circuitry may be provided in the electronic measurement device 1004 and/or the computer 1006.

In general, the size of the channels and the size of the cross-channel reaction area occupied by the porous membrane can be adjusted for the various reactants used in the test. The fluid or molecules can be made to flow using standard microfluidic methods such as hydrostatic, hydrodynamic, electrodynamic, electro-osmotic, magnetohydrodynamic, acoustic and ultrasonic, mechanical, induced electric fields, thermal and other known methods. The flow-through microchannel structure (as shown in fig. 1 a-1 f, 4 a-4 e, 5 a-5 e) allows flow rate control, fluid dilution, efficient channel washing, and minimal backflow. Alternatively, standard microfluidic components and devices may be utilized to block flow for conditioning, diffusion, dilution, and the like. For non-flow-in microchannel structures (as shown in fig. 2 a-2 e, 3 a-3 e, and 6 a-6 e), the number of inlets and outlets and the size of the cross-channel region may be varied according to functional requirements, reactant behavior, etc. Furthermore, a large number of parallel structures according to the principles described in the embodiments of fig. 4 a-4 e and 5 a-5 e can be fabricated and used for testing. In such an example, the porous membrane at each cross channel may have the same or different function (optical, biochemical, electrical, acoustical, etc.) as: sensors/detectors, molecular separation or screening filters, biological reaction devices (with surface modified nanopores, with immobilized biomolecule nanopores, surface coated nanopores, etc.).

While the invention has been illustrated and described with respect to a limited number of embodiments, the invention may be embodied in various forms without departing from the spirit of the essential characteristics thereof. Accordingly, the embodiments described and illustrated herein, including what is described in the summary of the invention, are to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims (27)

1. An apparatus, comprising:

a substrate having defined therein:

an upper microfluidic channel through the substrate in a first direction;

a lower microfluidic channel through said substrate in a second direction, a portion of said lower microfluidic channel passing below a portion of said upper microfluidic channel to form a cross-channel region; and

a porous membrane positioned between the upper microfluidic channel and the lower microfluidic channel and adjacent to the cross-channel region to form a semi-permeable barrier between the upper microfluidic channel and the lower microfluidic channel.

2. The device of claim 1, wherein the porous membrane comprises porous nanocrystalline silicon.

3. The device of claim 1, wherein the porous membrane comprises porous polysilicon.

4. The device of claim 1, further comprising a first reservoir defined in the substrate and connected in fluid communication with one of the upper microfluidic channel and the lower microfluidic channel.

5. The device of claim 4, further comprising a second reservoir defined in the substrate and connected in fluid communication with the other of the upper and lower microfluidic channels that is not connected in fluid communication with the first reservoir.

6. The device of claim 1, further comprising respective reservoirs defined at opposing ends of at least one of the upper and lower microfluidic channels.

7. The device of claim 1, wherein the porous membrane exhibits a sensing characteristic that causes a change in at least one of an optical and electrical characteristic in response to exposure to one or more specific solutes and/or analytes.

8. The device of claim 7, wherein the sensing characteristic comprises a change in an optical characteristic, and the device further comprises:

a light source for directing light to the porous membrane; and

a detector to receive a portion of the light reflected and/or emitted by the porous silicon membrane to detect a change in an optical characteristic of the porous membrane.

9. The apparatus of claim 8, further comprising a data collection device connected in fluid communication with the detector to collect data relating to the change in the optical property in the porous membrane.

10. The apparatus of claim 7, wherein the sensing characteristic comprises an electrical characteristic and the substrate further comprises a microelectronic circuit operatively coupled to the porous membrane.

11. The device of claim 10, further comprising an electronic measurement device coupled to the porous silicon membrane via the microelectronic circuitry to measure a change in an electrical characteristic of the porous silicon membrane when exposed to the one or more specified fluids.

12. The apparatus of claim 11, further comprising a data collection device connected in communication with the electronic measurement device.

13. The device of claim 1, wherein the porous membrane has a medium thickness ranging from 10 nanometers to 50 nanometers.

14. The device of claim 1, wherein the porous membrane has a plurality of pores of intermediate diameter ranging from 50 angstroms to 10 microns.

15. The apparatus of claim 1, wherein the substrate comprises one of: polydimethylsiloxane, silicon, quartz, polymer, or polymethylmethacrylate substrates.

16. An apparatus, comprising:

a substrate having defined therein:

a plurality of upper microfluidic channels through the substrate in a first direction;

at least one lower microfluidic channel through the substrate in a second direction, a respective portion of the at least one lower microfluidic channel passing under a respective portion of the upper microfluidic channel to form a plurality of respective cross-channel regions; and

at least one porous membrane positioned between the upper microfluidic channel and the lower microfluidic channel and adjacent to the cross-channel region to form a semi-permeable barrier between the upper microfluidic channel and the lower microfluidic channel in a corresponding region adjacent to the plurality of cross-channel regions.

17. The device of claim 16, wherein the at least one lower microfluidic channel is a plurality of channels, and the plurality of cross-channel regions are substantially arranged in an array.

18. The device of claim 16, wherein the at least one porous membrane is a plurality of porous membranes, each positioned adjacent to a respective cross-channel region.

19. The device of claim 16, wherein the at least one porous membrane comprises porous nanocrystalline silicon.

20. The device of claim 16, wherein the at least one porous membrane comprises porous polysilicon.

21. The device of claim 16, wherein the porous silicon membrane exhibits a sensing characteristic that causes a change in at least one of an optical and electrical characteristic in response to exposure to one or more specific solutes and/or analytes.

22. The device of claim 16, wherein the sensing characteristic comprises a change in an optical characteristic, and the device further comprises:

a light source for directing light to the porous membrane; and

a detector to receive a portion of the light reflected and/or emitted by the porous silicon membrane to detect a change in an optical characteristic of the porous membrane.

23. The apparatus of claim 16, wherein the sensing characteristic comprises an electrical characteristic and the substrate further comprises a microelectronic circuit operatively coupled to the porous membrane.

24. An apparatus, comprising:

a substrate having defined therein:

a plurality of upper microfluidic channels formed in said substrate, each upper microfluidic channel having a first end and a second end, said second ends converging at an intersection;

a lower microfluidic channel formed in said substrate having a first end located below said intersection; and

a porous membrane positioned between the upper microfluidic channel and the lower microfluidic channel and proximate to the intersection point to form a semi-permeable barrier between the upper microfluidic channel and the lower microfluidic channel.

25. The device of claim 24, further comprising a plurality of reservoirs in the substrate, each at the first end of a respective one of the upper microfluidic channels.

26. The device of claim 24, wherein the at least one porous membrane comprises one of porous nanocrystalline silicon or porous polycrystalline silicon.

27. The device of claim 24, wherein the porous membrane exhibits a sensing characteristic that causes a change in at least one of an optical and electrical characteristic in response to exposure to one or more specific solutes and/or analytes.