Ag/AgCl microelectrodes with improved stability for microfluidics

A method for fabricating Ag/AgCl planar microelectrodes for microfluidic applications is presented. Micro-reference electrodes enable accurate potentiometric measurements with miniaturized chemical sensors, but such electrodes often exhibit very limited lifetimes. Our goal is to construct Ag/AgCl microelectrodes reliably with improved potential stability that are compatible with surface mounted microfluidic channels. Electrodes with geometric surface areas greater than or equal to 100 μm2 were fabricated individually and in an array format by electroplating silver, greater than 1 μm thickness, onto photolithographically patterned thin-film metal electrodes. The surface of the electroplated silver was chemically oxidized to silver chloride to form Ag/AgCl micro-reference electrodes. Characterization results showed that Ag/AgCl microelectrodes produced by this fabrication method exhibit increased stability compared with many devices previously reported. Electrochemical impedance spectroscopy allowed device specific parameters to be extracted from an equivalent circuit model, and these parameters were used to describe the performance of the microelectrodes in a microfluidic channel. Thus, stable Ag/AgCl microelectrodes, fabricated with a combination of photolithographic techniques and electroplating, were demonstrated to have utility for electrochemical analysis within microfluidic systems.