Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device: An Overview

A novel type of sensor based on spectroelectrochemical techniques possessing three modes of selectivity is described. The selectivity of this type of sensor comes from the ability of the analyte to (1) partition into an ion-exchange film coating an optically transparent electrode (OTE), (2) undergo oxidation or reduction at a given potential, and (3) absorb light in either its oxidized or reduced form at the analytical wavelength. This review charts the development of this type of sensor from its inception, illustrating its ability to selectively sense target ions in the presence of various interferents, its limits of detection, and our attempts to modify and improve its performance in both of these areas. Also provided is an overview of how this type of sensor can be employed as a small, portable unit appropriate for field work; an example is its employment in the detection of ferrocyanide in tank waste at the Hanford nuclear waste site located near Richland, Washington. Such applications as this illustrate the effectiveness of the sensor design, especially when used in harsh, real-world conditions where many sensor prototypes fail.