Broadband Spectroelectrochemical Interrogation of Molecular Thin Films by Single-Mode Electro-Active Integrated Optical Waveguides

Abstract

AbstractElectron transfer processes to/from monolayers or submonolayers of surface-confined molecules are at the core of several established or emerging sensor technologies. Spectroelectrochemical techniques to monitor these redox processes combine spectroscopic information with the normally monitored electrochemical parameters, such as changes in current or voltage, and can be much more sensitive to changes in optical properties coupled with electron transfer than electrochemical techniques alone. Spectroelectrochemical techniques based on absorbance measurements typically suffer from low sensitivity owing to the low concentrations of redox active species on the surface, and their low absorptivities. Electro-active, single-mode waveguide technologies, developed over the last decade, have provided more than adequate sensitivity to characterize electron transfer to surface-confined molecules where the coverage can be as low as a few percent of a monolayer. In this chapter, we review the major developments in combining electrochemical analysis with optical platforms that maximize optical sensitivity, through the development of electro-active integrated planar waveguides operating in the single-mode optical regime. We provide here a general overview of the theoretical formalisms associated with light propagation and absorbance measurements in integrated optical waveguides, and their electro-active counterparts. We also describe the major implementations of the technology, including the extension of the single-mode configuration into a broadband spectroscopic tool to facilitate the interrogation of the entire visible wavelength region during the redox event, and review some specific applications of these techniques, which demonstrate its sensitivity and broad utility.KeywordsSpectroelectrochemistryIntegrated optical waveguidesElectrochemistryOptical absorbance