Electrochemically-modulated surface plasmon waves at a nano-scale for investigations and applications of redox assemblies.

Abstract

In this thesis, an electrochemically-modulated surface plasmon resonance (EC-SPR) technique was developed for challenging investigations and applications in different redox assemblies. The principle of the technique is based on the nano-scale confined and sensitive interplay between a surface plasmon wave and a redox-active probe featuring an optical transition when undergoing a faradaic redox process. Such faradaic process is electrochemically controlled by modulating the surface electric potential of the SPR platform to create an optical output signal that is substantially immune to the negative impacts of background environment and enabling the identification and quantification minute properties linked to a molecular event of interest. First, the structure of the EC-SPR platform and the ideal experimental conditions to optically interrogate it were investigated. Different strategies were examined for the ideal SPR configuration to enhance the spectroelectrochemical response imprinted into the optical signal. A redox active probe, the cytochrome c protein, was used as a model system to report the performance of the EC-SPR device and to confirm its suitability for spectroelectrochemical measurements. Experimental measurements of SPR reflectance curves and numerical analysis of the experimental data based on a developed Mathematica code were implemented to support the rationale design of SPR configurations aiming to maximize the optical response linked to a redox process and to ultimately reach a high performance for the EC-SPR platform. Next, a combination of the EC-SPR device and the optical impedance spectroscopy technique (OIS) was demonstrated to provide an effective analytical path to study electron transfer rates in redox species. When compared to competing technologies, the major advantages of this combination are the ability to implement the device over a broad range applied electric potentials and to reach high modulation frequencies. These features increase the capability of the EC-SPR technology for investigations and applications of fast reaction rate constants for a wider range of surface-adsorbed redox species. The capability of the EC-SPR device for determining electron-transfer rates was experimentally demonstrated here. The electron-transfer rate of a redox probe, cytochrome c protein, immobilized at different functionalized assemblies on the plasmonic interface were investigated. The results show that each functionalized layer has a strong impact on the electron-transfer rate of a redox probe interacting with the functionalized electrode of the EC-SPR platform. The quantification and understanding of the electrochemical behavior of these functionalized layers and the ability of the EC-SPR platform to monitor the electron-transfer rate of biomolecular assemblies provide the groundwork