Date of Award
Doctor of Philosophy in Chemistry
The charge transfer across the liquid/liquid interface has been playing a crucial role in many biological and energy-related systems such as drug permeation through-bacterial membrane, ion or electron transfer through metal-reducing bacteria in microbial fuel cells (MFCs), and metabolic interaction in commensal bacterial species related to human health. Primarily, direct probing of these phenomena in situ is needed for more realistic fundamental analysis, thereby solving the problem related to public health and renewable energy generation. The interfacial CT in these systems mainly involves redox-inactive species that cannot be detected with conventional metal electrodes. Herein, the liquid/liquid interface is applied as an analytical tool to probe (1) antimicrobial permeation through the membrane, (2) microbial fuel oxidation, a core step of extracellular electron transfer pathways in MFCs, and (3) metabolic interaction between oral commensal bacteria relevant to human health. In my first project, we studied the transport kinetics of pristine antimicrobials, e.g., quinolones, and sulfonamides using a nanopipet-supported liquid/liquid interface as a mimic of a biological membrane as well as a probe. Finite element analysis of experimental voltammograms revealed a relationship between the structure of hydrophobic drug ions and their permeation across the interface. While the metal-reducing bacteria produces CO32- and electrons during organic fuel oxidation, a novel probe is highly demanded to assess this mechanism in real time to quantitatively elucidate extracellular electron transfer in this bacterial system. In my second project, we developed nanoscale CO32- amperometric ion-selective electrodes (ISEs) based on ionionophore recognition using Simon’s ionophore, and fundamentally investigated hidden barriers to the development of this nanoscale ISE. The experimentally and theoretically II proved fundamental understanding enabled us to mechanistically and kinetically evaluate the interfacial CO32- ion transfer reaction facilitated by ionophore as well. The analytic utility of our probe was further verified by quantifying CO32- produced by metal-reducing bacteria. In the third project, we applied a nanopiet-supported liquid/liquid interface as a probe and nanoscale scanning electrochemical microscopy (SECM) to in situ investigate metabolic interaction between oral commensal bacterial species related to human health. Herein, we could real-time visualize and quantitatively assess the metabolite exchange between two bacterial species via lactate production and consumption rate at a single-cell level. These findings will help to monitor potential disease risks in humans by probing multi-species metabolic interaction. We will further employ this nanoscale probe and nanoscale SECM to study drug resistance in real bacteria, and extracellular electron transfer pathways in MFC at a single-cell level.
Puri, Surendra R., "NANOSCALE ELECTROCHEMISTRY AT LIQUID/LIQUID INTERFACE FOR BIOMEDICAL AND ENERGY APPLICATIONS" (2023). Open Access Dissertations. Paper 1533.