Electrochemical Measurements with Interdigitated Array Microelectrodes

ing into widespread use for the trace determination of easily oxidizable and reducible organic and inorganic compounds, because it provides a rather easy procedure for direct and selective detection. Recently, microelectrodes have been receiving attention in this field (1,2). They offer higher sensitivity than macroelectrodes of conventional size, because an electroactive molecule can approach the microelectrode from every direction (spherical diffusion). Therefore, the flux of electroactive molecules toward the electrode is much greater for a microelectrode than for a macroelectrode, for which the diffusion is planar. Spherical diffusion has been utilized in sensor devices (3), detection of intermediate species, reaction analysis (4), electrochemistry in highly resistive media (5), and organic electronic devices (6). The characteristics of microelectrodes depend on their shapes and arrangements. Mathematical solutions for each kind of electrode response predict the superior electrode sensitivity of microelectrodes (7). Although microelectrodes offer many advantages, they are not easy to construct, which limits their availability. They have been fabricated with metal or carbon wire in a glass tube by grinding the cross section of the tube, but this method has poor reproducibility and makes it difficult to control the electrode’s shape. By using photolithography for the fabrication of microelectrodes, complex and arbitrary shapes and sizes of electrodes can be made with excellent reproducibility. This technique is also suitable for mass production of microelectrodes. One of the most prominent examples of this kind of electrode is an interdigitated array (IDA) microelectrode. The IDA electrode consists of a pair of microband array electrodes that mesh with each other. Each set of microband electrodes in the IDA can be potentiostated individually, so a reduced species generated at one microband electrode diffuses across a small gap to the adjacent electrode, and then is oxidized and diffuses back to the original electrode. This redox cycling increases the currents at both electrodes. The concept of this electrochemical technique is similar to that at a rotating ring-disk electrode, but offers several advantages: steady-state currents can be achieved in a very short time, collection efficiency approaches unity, and handling and installing the electrode are simple. Pioneering work was done on the IDA by Sanderson and Anderson (8), and several applications have been reported (9–12). Tabei and co-workers have extensively studied the characteristics of the IDA electrode and its applications in electrochemistry (13). In this article, fundamental considerations and the applications of IDA electrodes in electrochemistry are described. Electrochemical Measurements with Interdigitated Array Microelectrodes