Rapid prototyping of microfluidic switches in poly(dimethyl siloxane) and their actuation by electro-osmotic flow

This paper describes a procedure for rapidly and conveniently prototyping m icrofluidic devices that are useful with aqueous solutions. A design (with diameters of channels greater than or equal to 20 mu m) is created in a com puter-aided design program and printed at high resolution on a transparency . This transparency is used as a mask in photolithography to create a maste r in positive relief photoresist: casting poly(dimethyl siloxane) (PDMS)aga inst this master yields a polymeric replica containing a network of bas-rel ief channels. The channels are closed and sealed irreversibly by oxidizing the replica and another flat substrate (PDMS, glass, silicon, silicon oxide ) in an oxygen plasma and bringing the two surfaces into conformal contact. Oxidation of the polymer allows the formation of a seal without using adhe sives: it also generates channels that support electro-osmotic flow (EOF) a nd fill easily with aqueous solutions. Two microfluidic devices-a fluidic s witch and a side channel flow controller-have been fabricated using this ra pid prototyping methodology. These devices were tested using aqueous soluti ons as the test fluid and actuated by EOF.