Spectroelectrochemical sensing: Novel thin film characterization and multiple analyte detection

Spectroelectrochemical sensors uniquely employ electrochemistry, spectroscopy, and a chemically selective film in a single device. The advantage to combining these three components is to achieve a higher level of selectivity. The three "modes of selectivity" exclude interferences from the sensor response based on the analyte's electrochemical, optical, and ionic characteristics. Furthermore, the implementation of the selective film also helps to achieve a lower level of sensitivity due to its ability to concentrate the analyte at the sensing surface. To be detected, the analyte must: (1) partition into the film, (2) be electrochemically active in the selected potential window, and (3) either the analyte or its electrolysis product must absorb or emit light at the monitored wavelength. Analyte detection is based upon a change in optical response due to the conversion of the analyte between two oxidation states that results from the stepping or cycling of the applied potential.;The Chemical Sensors research group at the University of Cincinnati has been working to develop and improve this sensing method. This dissertation presents the results of research completed on two aspects of this project. The first study includes the characterization and performance of a novel selective film material, sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SSEBS). The ability of the film to preconcentrate analytes, as well as exclude interferences, was examined. Furthermore, the diffusion coefficient of a redox probe (Ru(bpy)32+) in the film was calculated using chronoamperometry and cyclic voltammetry.;In the second study, a novel method is demonstrated for using the spectroelectrochemical sensor for multiple analyte detection. Prior to this study, the spectroelectrochemical sensor has detected non-ideal analytes in one of two ways: (1) weakly absorbing metal ions bind with an organic ligand in-situ to form a complex that has the desired characteristics, or (2) weakly absorbing metal ions are deposited onto, and then stripped from the bare electrode using anoidic stripping voltammetry, which also results in the desired change in optical response. The novel method demonstrated in this dissertation combines these two approaches to the detection of non-ideal analytes into a single experiment. Potential limitations of this method, such as ASV at a chemically modified electrode and metal ion competition for the complexing ligand and ion-exchange sites in the selective film, were also investigated.