Ag/AgCl Film Electrodes Coated with Agarose Gel as Planar Reference Electrodes for Potentiometric Sensors

Abstract

Silver/silver chloride (Ag/AgCl) is commonly used as a reference electrode in electrochemical measurements. However, commercial macroscopic Ag/AgCl electrodes cannot be used in micro-electrochemical sensors. Thus, many scientists are trying to miniaturize reference electrodes to integrate into one sensor chip. In this paper a new approach for fabrication of Ag/AgCl thin films coated with agarose gel as planar reference electrodes for potentiometric sensors is introduced. A silver thin film of 220-250 nm was sputtered and patterned on silicon dioxide/ silicon substrates by lithography and lift-off techniques. A AgCl layer was coated on the Ag film by using a Ag[NH3]2Cl complex at 80℃ in vacuum. The thickness of the AgCl layers was about 5um. The Ag/AgCl layers were then coated with an agarose gel. The AgCl layers were characterized by X-ray diffraction, micro Raman spectroscopy and scanning electron microscopy. The Open Circuit Potential (OCP) measurements with the fabricated electrodes as reference electrodes in pH 7 buffer solutions were performed in comparison with a commercial Ag/AgCl electrode. The potential difference between the fabricated Ag/AgCl electrodes and the commercial Ag/AgCl electrode was insignificant. The coating of the agarose layer as a protection layer of the Ag/AgCl electrodes enhanced the durability of the modified electrodes. The results indicated that the fabricated Ag/AgCl thin films coated with the agarose gel could be used as planar reference electrodes for potentiometric sensors.