Rapid prototyping of microfluidic systems in poly(dimethylsiloxane)

This paper describes a procedure that makes it possible to design and fabri cate (including sealing) microfluidic systems in an elastomeric material-po ly(dimethylsiloxane) PDMS)-in less than 24 h. A network of microfluidic cha nnels (with width >20 mu m) is designed in a CAD program. This design is co nverted into a transparency by a high-resolution printer; this transparency is used as a mask in photolithography to create a master in positive relie f photoresist, PDMS cast against the master yields a polymeric replica cont aining a network of channels. The surface of this replica, and that of a fl at slab of PDMS, are oxidized in an oxygen plasma. These oxidized surfaces seal tightly and irreversibly when brought into conformal contact. Oxidized PDMS also seals irreversibly to other materials used in microfluidic syste ms, such as glass, silicon, silicon oxide, and oxidized polystyrene; a numb er of substrates for devices are, therefore, practical options. Oxidation o f the PDMS has the additional advantage that it yields channels whose walls are negatively charged when in contact with neutral and basic aqueous solu tions; these channels support electroosmotic pumping and can be filled easi ly with liquids with high surface energies (especially water). The performa nce of microfluidic systems prepared using this rapid prototyping technique has been evaluated by fabricating a miniaturized capillary electrophoresis system. Amino acids, charge ladders of positively and negatively charged p roteins, and DNA fragments were separated in aqueous solutions with this sy stem with resolution comparable to that obtained using fused silica capilla ries.