An iridium oxidereference electrode for use in microfabricated biosensors and biochips

Abstract

In this paper we argue for the use of iridium oxide (IrO_x) electrodes as quasi-reference electrodes in microfabricated biosensors and biochips that operate in buffered solutions. The simple microfabrication of these electrodes consists of a one-step electrodeposition of IrO_x onto a microfabricated platinum (Pt) electrode. The IrO_x electrode potential was found to vary less than 20 mV over 9 days after stabilization for 1 day in a phosphate-buffered saline (PBS) solution; this behavior of the electrode potential was found to be easily reproduced. Moreover, the electrode potential was found to vary by less than 15 mV in the initial hour of its use; this behavior of the electrode potential was also found to be reproducible. The performance of a microfabricated glucose sensor employing an IrO_x reference electrode is characterized in this paper in order to evaluate the usefulness of this new IrO_x electrode as a quasi-reference electrode. The glucose sensor consists of a recessed microfabricated Pt electrode array, an electrodeposited IrO_x film, an inner layer composed of an electropolymerized poly(m-phenylenediamine)/glucose oxidase (PMPD/GOx) film, and an outer or protective layer composed of Teflon and polyurethane (PU) films. The response of this sensor was found to be equivalent to the response of the same sensor employing a commercial Ag/AgCl reference electrode. These results show that a microfabricated IrO_x electrode can be used as a quasi-reference electrode in microfabricated biosensors and biochips operating in buffered solutions.