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Microfluidic devices with porous membranes for molecular sieving, metering, and separation of analyte fluids. In one aspect, a microfluidic device includes a substrate having input and output microfluidic channel sections separated by a porous membrane formed integral to the substrate. In another as

Microfluidic devices with porous membranes for molecular sieving, metering, and separation of analyte fluids. In one aspect, a microfluidic device includes a substrate having input and output microfluidic channel sections separated by a porous membrane formed integral to the substrate. In another aspect, the porous membrane may comprise a thin membrane that is sandwiched between upper and lower substrate members. The microfluidic device may include one or a plurality of porous membranes. In one embodiment, a plurality of porous membranes having increasingly smaller pores are disposed along portions of a microfluidic channel. In another embodiment, a cascading series of upper and lower channels are employed, wherein each upper/lower channel interface is separated by a respective porous membrane. In another aspect, a porous membrane is rotatably coupled to a substrate within a microfluidic channel via a MEMS actuator to enable the porous membrane to be positioned in filtering and pass-through positions.

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What is claimed is: 1. A microfluidic device, comprising: a substrate platform comprising a plurality of cascading microfluidic channels including respective pairs of upper and lower microfluidic channels; and a plurality of porous membranes, each disposed between end portions of a respective pair

What is claimed is: 1. A microfluidic device, comprising: a substrate platform comprising a plurality of cascading microfluidic channels including respective pairs of upper and lower microfluidic channels; and a plurality of porous membranes, each disposed between end portions of a respective pair of upper and lower microfluidic channels and comprising a semi-permeable barrier having a plurality of pores to selectively filter an influent fluid that may be introduced in an upper microfluidic channel on an input side thereof to produce a filtered effluent fluid in the lower microfluidic channel on an output side thereof. 2. The microfluidic device of claim 1, wherein each of the plurality of porous membranes are integrally formed from the substrate. 3. The microfluidic device of claim 1, further comprising a cover disposed over at least a portion of the microfluidic channel. 4. The microfluidic device of claim 1, wherein the substrate platform comprises a plurality of substrate layers, each having at least one of an upper microfluidic channel and a lower microfluidic channel formed therein. 5. The microfluidic device of claim 1, wherein the substrate platform comprises an upper and lower substrate member sandwiched around the plurality of porous substrates upon assembly. 6. The microfluidic device of claim 1, further comprising a plurality of reservoirs disposed along a flow path passing along the plurality of cascading microfluidic channels. 7. The microfluidic device of claim 1, wherein the plurality of cascading microfluidic channels are substantially serpentine in configuration. 8. A method for fabricating a microfluidic device of claim 1, comprising: forming the plurality of cascading microfluidic channels in a silicon substrate comprising a plurality of channel segments separated by one or more silicon gaps; and etching said one or more silicon gaps to form the semi-permeable barrier. 9. The method of claim 8, wherein said one or more silicon gaps are etched using electrochemical etching or stain etching. 10. A microfluidic device, comprising: a substrate having a microfluidic channel formed therein; and a porous membrane disposed within the microfluidic channel and rotatably coupled to the substrate such that when the porous membrane is rotated to a filtering position it operates as a semi-permeable barrier having a plurality of pores to selectively filter an influent fluid that may be introduced in the microfluidic channel on an input side of the porous membrane to produce a filtered effluent fluid on an output side of the porous membrane, and when the porous membrane is rotated to a pass-through position fluid flowing through the microfluidic channel is enabled to freely bypass the porous membrane. 11. The microfluidic device of claim 10, wherein the porous membrane is hingedly coupled to the substrate via a first Micro-Electro-Mechanical System (MEMS) actuator. 12. The microfluidic device of claim 10, further comprising a cover coupled to the substrate and disposed over at least a portion of the microfluidic channel. 13. The microfluidic device of claim 10, further comprising a second MEMS actuator for locking the porous membrane in the filtering position.