Microfabricated Liquid Junction Ag/AgCl Reference Electrode and Its Application to a One-Chip Potentiometric Sensor

Abstract

A liquid-junction Ag/AgCl reference electrode was microfabricated. A silver thin-film pattern was covered with a polyimide protecting layer with a 50-μm-wide slit at the center of the pattern, and the AgCl layer was grown from there into the silver layer. A liquid junction was formed with a photocurable hydrophilic polymer. The electrolyte layer was formed by screen-printing a paste containing fine KCl powder. A silicone rubber passivation covered the entire area except for the pad and the end of the junction. The novel thin-film Ag/AgCl element could maintain its expected potential for longer than 30 h in a saturated KCl solution. The completed miniature liquid-junction reference electrode could maintain a stable potential level within ±1 mV for longer than 100 h with the aid of a poly(vinylpyrrolidone) (PVP) matrix in the electrolyte layer. Fluctuation of the potential was less than 0.1 mV at each moment. Dependency on external KCl concentration and pH was shown to be insignificant. The miniature refere...