Sensors Based on Spectroelectrochemistry: Detection of Metal Ions

Abstract

Spectroelectrochemical sensors for detecting metal ions have been developed by combining electrochemistry, spectroscopy, and selective partitioning into a single device. The sensor consists of an optically transparent electrode (OTE) coated with a thin (20-500 nm thick) charge-selective film. Sensing is based on the change in optical signal for attenuated total reflectance (ATR) at the OTE accompanying electrochemical modulation of the analyte that has partitioned into the film. Two properties of the analyte that are important for its sensitive detection are a large optical signal from one of the two oxidation states involved in electrochemical modulation and high loading into the charge-selective film. However, not all metal ions have appropriate spectroscopic properties for sensitive detection. This paper focuses on two strategies for improving sensitivity for metal ions: (a) increasing the molar absorptivity difference between the electromodulated oxidation states and (b) enhancing preconcentration of analyte into the charge-selective film.