Highly sensitive detection of reversible species by self-induced redox cycling

Abstract

Microelectrodes have been attracting much attention, because of their small IR drop, fast establishment of steady-state mass transfer, and small capacitive charging currents. Various types of electrode including microdisks, microbands or arrays of microelectrodes, have been documented both experimentally and theoretically [l-14]. The use of two potentiostated working electrodes such as the interdigitated array (IDA) microelectrodes has been of particular interest because of their high sensitivity and fast response time in the electrochemical analysis of reversible species [15-171. Since each electrode in the pair can be potentiostated separately, an electroactive species generated at one of the electrodes can diffuse to the other. The diffusion of the redox species takes place in a confined space resulting in a steady-state concentration gradient between the twin microelectrodes. This steep gradient leads to a large limiting current with a high S/N ratio. However, it is desirable to use a conventional instrument without a twin potentiostat for analytical applications. Recently, we reported a limiting current enhancement by self-induced redox cycling at a closely spaced micro-macro twin electrode without the use of a twin potentiostat, and the magnitude of the limiting current was equal to that obtained with a twin potentiostat [18]. A novel micro-macro twin electrode and conventional electrochemical techniques for single working electrodes were applied to the highly sensitive voltammetric detection of redox species. Figure l(a) shows the novel micro-macro electrode structure, which was fabricated by photolithographic techniques. This electrode consists of a closely spaced interdigital twin gold electrode. The twin gold electrode is composed of a microband array electrode (microelectrode) and a