Patterning of platinum microelectrodes in polymeric microfluidic chips

Abstract

Miniaturized electrodes are one of the most important components of lab-on-a-chip devices for separation, pumping, sensing, and other bioanalyses. In microfluidic-based chemical and bioanalytical operations, platinum electrodes are preferred to minimize the interaction with chemicals or biomolecules due to their chemical inertness. Although microfabrication techniques for patterning integrated platinum microelectrodes on silicon, quartz, or glass substrates are available, no techniques have been reported so far for depositing platinum electrodes in soft polymeric microchannels. A novel fabrication scheme is described for forming integrated microelectrodes in a poly-di-methyl-siloxane (PDMS) microchip. The electrode fabrication technique consists of photolithography, thermal processing, sequential sputtering of titanium and platinum, and stripping off photoresist, while soft lithography is used to form the microfluidic channels on PDMS. This approach facilitates precise positioning of the electrodes with a micron-size gap between them, and it can be used for both low and high aspect ratio channels. Platinum electrodes, formed on the PDMS channel surface, demonstrate very good interfacial adhesion with the substrate due to the use of a very thin titanium layer between the platinum and PDMS. The sputtered electrodes have a surface roughness of 50 nm and are able to sense picoA level current through benzene.