Date of Award

Spring 4-2017

Embargo Period

5-1-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical Engineering

Advisor(s)

Mohammad Islam

Abstract

The development of enzymatic biosensors and enzymatic biofuel cells (EBFCs) has been a significant area of research for decades. Enzymatic catalysis can provide for specific, reliable sensing of target analytes as well as the continuous generation of power from physiologically present fuels. However, the broad implementation of enzyme-based devices is still limited by low operational/storage stabilities and insufficient power densities. Approaches to improving upon these limitations have focused on the optimization of enzyme activity and electron transfer kinetics at enzyme-functionalized electrodes. Currently, such optimization can be performed through enzyme structural engineering, improvement of enzyme immobilization methodologies, and fabrication of advantageous electrode materials to enhance retained enzyme activity density at the electrode surface and electron transfer rates between enzymes and an electrode. In this work, varying electrode materials were studied to produce an increased understanding on the impacts of material properties on resulting biochemical, and electrochemical performances upon enzyme immobilization and an additional method of electroactive enzyme-based optimization was developed through the use of polymer-based protein engineering (PBPE). First, graphene/single-wall carbon nanotube cogels were studied as supports for membrane- and mediator-free EBFCs. The high available specific surface area and porosity of these materials allowed the rechargeable generation of a power density within one order of magnitude of the highest performing glucose-based EBFCs to date. Second, two additional carbon nanomaterial-based electrode materials were fabricated and examined as EBFC electrodes. Graphene-coated single-wall carbon nanotube gels and gold nanoparticle/multi-wall carbon nanotube-coated polyacrylonitrile fiber paddles were utilized as electroactive enzyme supports. The performance comparison of these three materials provided an increased understanding of the impact of material properties such as pore size, specific surface area and material surface curvature on enzyme biochemical and electrochemical characteristics upon immobilization. Third, PBPE techniques were applied to develop enzyme-redox polymer conjugates as a new platform for enzymatic biosensor and EBFC optimization. Poly(N-(3-dimethyl(ferrocenyl) methylammonium bromide)propyl acrylamide) (pFcAc) was grown directly from the surface of glucose oxidase (GOX) through atom-transfer radical polymerization. Utilization of the synthesized GOX-pFcAc conjugates led to a 24-fold increase in current generation efficiency and a 4-fold increase in EBFC power density compared to native GOX. GOX-pFcAc conjugates were further examined as working catalysts in carbon paper-based enzymatic biosensors, which provided reliable and selective glucose sensitivities and allowed a systematic analysis of sources of instability in enzyme-polymer conjugate-based biosensors and EBFCs. The knowledge gained through these studies and the in-depth characterization of an additional layer of optimization capacity using PBPE could potentially enhance the progress of enzymatic biosensor and EBFC development.

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