From Microelectrodes to Scanning Electrochemical Microscopy

This chapter considers advances in electroanalytical chemistry which resulted from the development of microelectrodes, an area of research where Martin Fleischmann made significant theoretical and experimental contributions. Briefly, a microelectrode is defined as an electrode with at least one dimension sufficiently small (typically less than 50 μm) that its amperometric properties are a function of this characteristic length [1, 2]. Historically, the development of microelectrodes resulted from the needs of biologists to perform measurements in real biological systems. For this, tiny electrodes were required to operate in situ, typically in vivo, and to offer localized recordings without affecting the integrity of the biological tissues. Hence, as early as 1942 electrophysiologists were developing micrometersized electrodes to determine,amperometrically, the concentration of dissolved oxygen in animal tissues [3]. Subsequently, efforts moved on to the development of potentiometric microelectrodes [4, 5], and it was not until the 1970s that the advantages of amperometry at micrometer-sized electrodes began to be fully recognized, primarily for the ability to perform voltammetry in vivo, especially in studies of neurotransmitters [6, 7]. Although, previously, the electrochemical fraternity had frequently referred to microelectrodes, these were in fact millimeter-sized electrodes; consequently, in order to avoid confusion the truly micrometer-sized electrodes were denoted ultramicroelectrodes (UMEs)during the early 1980s [8–10].