Microfabricated thin-film reference electrode for disposable electrochemical sensors

Abstract

For an electrochemical sensor to perform accurate and reliable measurement, having a reference electrode with consistent potential is required. This predetermined potential is the reference point to which either controlled or measured potential of the working electrode is compared. Generally, conventional silver/silver chloride (Ag/AgCl) reference electrodes with aqueous inner electrolyte are the most preferred ones as preparation of the electrodes is relatively easy and inexpensive. The nontoxic and robust properties of these reference electrodes also promote the popularity of usage. However, the bulky size together with the involvement of aqueous electrolyte inside the electrodes hinders their ability to be directly integrated with portable or disposable electroanalytical devices. To circumvent this issue, solid-state reference electrodes without aqueous electrolyte have become potential alternatives to replace the conventional reference electrodes. This paper presents a solidstate, thin-film Ag/AgCl reference electrode fabricated through direct evaporation of AgCl onto a layer of sputtered Ag. The performance of the microfabricated reference electrode has been electrochemically investigated in the aspects of a) stability over a range of scan rates, b) stability over a prolonged period of measurement, and c) consistency among multiple devices. Experimental results reveal that such type of reference electrode is able to provide stable potential reference, which suggests a promising application for disposable electrochemical sensors.