Fluorescence-Enabled Electrochemical Microscopy and Nanoscale Electrochemical Analysis

Thesis (Ph.D.)--University of Washington, 2013This dissertation discusses the fundamental study of several electroanalytical chemistry tools and methods. Unifying factors between the various chapters include the use of nano and microscale materials for electrode fabrication and the extensive use of voltammetric techniques for substrate characterization. Chapter 1 briefly introduces the technique of voltammetry and describes its importance in electrode characterization. This is followed by a short discussion of the methods and tools presented in upcoming chapters. In chapter 2 we highlight the development of fluorescence-enabled electrochemical microscopy (FEEM) and demonstrate an application towards heterogeneous catalyst screening. The FEEM technique uses a closed bipolar electrode (BPE) or arrays of many BPEs to couple the oxidation of an ordinary redox analyte to the fluorogenic reduction of a special reporter molecule. Optically monitoring the progress of the fluorogenic reaction allows for the indirect monitoring of the current through the BPE. Due to the importance of closed BPEs in the development of FEEM a detailed fundamental study of these electrodes was conducted. This work, which introduces the theory and experimental description of closed BPEs and discusses the factors to consider when using these electrodes for chemical analysis is presented in chapters 3 and 4. Next in chapter 5 we discuss the fabrication and voltammetric response of gold nanotrench electrodes. This includes the development of an analytical expression to correlate the recess depth to the diffusion-limited electrochemical response of these electrodes. Computational simulations and experimental findings are used to validate the theoretical model. Finally chapter 6 presents the first experimental demonstration of the scan-rate dependence of the non-linear current-voltage response commonly observed in conical quartz nanopores. We explain this behavior in terms of the sluggish redistribution of ions in the vicinity of the nanopore mouth upon voltage changes