Fabrication of robust 2-D and 3-D microfluidic networks for lab-on-a-chip bioassays

We describe a new method for the fabrication of robust three-dimensional (3-D) lab-on-a-chip devices comprising microfluidic channels and integrated electroanalytical sensors and show their potential application in supporting leak-free pressure driven fluid flow. The technology is based upon the lithographic patterning of a soluble negative photoresist and an insoluble, crosslinked, positive photoresist (SU-8) to produce the pattern of a large area microfluidic network, followed by coating the pattern with silicone rubber or PDMS. After curing, immersion in acetone rapidly elutes the soluble resist to yield the network of channels. As a result the channels formed are robust and it is possible to fabricate a device that supports fluids flowing at high flow rates (without leakage) without the need for special pre-treatment or surface modification of the substrate or silicone covering. We also demonstrate the flexibility of the methodology by producing more complex fluidic networks that comprise bridges which enable one fluid stream to pass over (and remain physically separated from) a second fluid stream. The sealing and packaging techniques, developed for this process do not require the use of extreme conditions and are thus compatible with a broad range of lithographic processes (including, for example, the definition of and incorporation of in situ electrochemical sensor elements). Finally, measurements on a model bioelectroanalytical system applicable to analysis of a model immunoassay are shown, demonstrating the application of this new fabrication method in developing reproducible analytical methods within an encapsulated device.