Electron-Transfer Kinetics in Protein Assemblies by Single-Mode Electro-Active Integrated Optical Waveguides

Abstract

An optical impedance spectroscopy (OIS) technique based on a single-mode electro-active integrated optical waveguide (EA-IOW) was developed to investigate electron-transfer processes of redox adsorbates. A highly sensitive single-mode EA-IOW device was created to optically follow the time-dependent faradaic current originated from a sub-monolayer of cytochrome c protein species undergoing redox exchanges driven by a harmonic modulation of the electric potential at several DC bias potentials and at several frequencies. To properly retrieve the faradaic current density from the AC-modulated optical signal we introduce a mathematical formalism that i) accounts for intrinsic changes that invariably occur in the optical baseline of the EA-IOW device during potential modulation and ii) provides accurate results for the electrochemical parameters. We experimentally demonstrate the optical reconstruction of the faradaic current density, identify the formal potential and energy-width of the electron-transfer process, and determine the reaction rate constant of the charge-transfer process. Our experimental approach brings additional sensitivity, accuracy, and simplicity to electrochemical analysis, and is expected to become a useful tool in investigations of currently challenging redox processes.