Mahadevan, Aishwarya (2019-07). IRON-SULFUR BASED MOLECULAR WIRES FOR ENHANCING CHARGE TRANSPORT IN ENZYMATIC BIO-ELECTRODES. Doctoral Dissertation.
Thesis
Iron-sulfur complexes, the first link between proteins and mediating molecules in the biological electron transport chain(s), possess intrinsic electron transport capabilities. In this work, the application of inorganic iron-sulfur clusters ([Fe-S]) viz. FeS, FeSv2, Fev2Sv3, and Fev3Sv4, as molecular wires to mediate electron transport between a glucoseselective redox enzyme and the gold electrode is studied using voltammetry methods. It is shown that [Fe-S] can emulate the functionality of the natural electron transport chain. Voltammetry studies indicate a significant improvement in electron transport, surface coverage, and resilience achieved by the [Fe-S]-based glucose anodes when compared to a conventional pyrroloquinoline quinone (PQQ)-based glucose anode. Next, the ability of [Fe-S] to perform electron transport ex vivo once wired to redox coenzymes (NAD/NADP, FAD, PQQ, and CoQv10) is studied using electrochemical methods. The formation of layer-by-layer self-assembled monolayers of the [Fe-S] and the coenzymes on Au surface was confirmed using cyclic voltammetry. Results indicated that [Fe-S] effectively anchors the redox coenzymes to gold electrodes and shuttles electrons between the two. Fourier-transform infrared spectroscopy (FTIR) and secondary ion mass spectrometry (SIMS) on FeS-NAD complex showed the FeS and NAD interacted via iron carbonyl bond formation. Reductive desorption studies revealed that, among the inorganic [Fe-S], Fev3Sv4-functionalized electrodes had the highest surface coverage, the lowest resistance and highest power requirements for monolayer desorption. Upon testing for a biosensing application, a 77% increase in sensitivity and a 53% improvement in detection limit was observed for a FeS-based glycerol biosensor when iii compared to the conventional PQQ-based counterpart, for glycerol concentration ranging from 1-25 mM. When tested to construct glucose-selective bioanode, a combination of FeS and Fev3Sv4 combined with BDT (an aromatic thiol linker) gave promising performances when used as a glucose sensor and a fuel cell. Thus, using multiple forms of inorganic iron-sulfur clusters, the ability of direct and robust wiring of the enzyme active site to an electrode while eliminating the issue of constrained charge transport endemic to bioelectronic systems is demonstrated. These discoveries are expected to create archetypes for wiring biological molecules where charge transport is critical - especially in bioelectronics systems.
