Development of a Reference Electrode Chip for Application in Ion Sensor Arrays

Abstract

Abstract A reliable screen-printing technique for fabricating an Ag/AgCl reference electrode on a solid substrate in a simple two-step procedure, which allows the incorporation of four different ion-selective electrodes on a chip, is presented. A ‘sandwich’ composite structure, comprising the reference electrode and a chip, was fabricated as a junction polymer membrane having an inner electrolyte layer and an Ag/AgCl electrode supported on a ceramic substrate. The junction polymer membrane was composed of chloroprene rubber, and the electrolyte layer was formed from agar gel. The electrochemical characteristics and performance of the reference electrode when integrated into a chip were investigated. From the results, it was shown that the potential change at the reference electrode chip as a function of the chloride ion concentration and pH can be kept reliably small. Its potential was also independent of the presence of other, physiologically significant, ions such as Ca2+, K+ and Li+. The reference electrode, fabricated as a chip, can be used continuously for more than 60 h. Furthermore, its integration with four different ion-selective electrodes (potassium, sodium, ammonium, and calcium) on a substrate to form an ion sensor array chip was shown to be a facile process. The integration procedures and the sensing performances of the ion sensor array chip are also described.