Development of Mediated Enzymatic Fuel Cells for Operation in Blood
Mac Aodha, Domhnall
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The process of enzymatic catalysis of glucose oxidation releases electrons which, when harnessed to flow through a circuit, may be utilised to power devices. This principle has driven research towards the goal of providing implantable medical devices powered by the fuel and oxidant present in-vivo, namely glucose and oxygen respectively. Challenges exist in the form of efficiently converting chemical energy into electrical energy, communicating the chemical process to an electrode, achieving both these aims under physiological conditions over a sufficient period of time, and, in so doing, creating enough electrical energy to power a device. This thesis builds on, and draws from, over three decades of development in the field of biomolecular electronics. Enzyme electrode assembly methodologies are developed, compared, and analysed in order to improve catalytic current density and stability for glucose oxidation. The inclusion of carbon nanotubes and implementation of alternate crosslinking strategies are investigated, and a novel method of enzyme electrode preparation is established. An enzyme electrode prepared with the addition of multi-walled carbon nanotubes, and co-immobilisation of glucose oxidase with a redox polymer-bound osmium mediator, crosslinked using glutaraldehyde vapour and subsequently reduced with sodium borohydride, is demonstrated to achieve 4.7 milli A /cm^2 glucose oxidation current density in phosphate buffer solution (pH 7.4, 37 °C, 150 milli M NaCl) in the presence of 100 milli M glucose, and retain almost 80% of that current over 24 hours, measured at an applied potential of 0.35 V (Chapter 2). Glucose oxidising and oxygen reducing enzymes are co-immobilised with redox polymer-bound osmium mediators in films upon electrodes, with the addition of multi-walled carbon nanotubes and crosslinked with glutaraldehyde vapours, and compared under pseudo-physiological conditions (Chapters 3-4). Building upon these results fully enzymatic glucose-oxidising, oxygen-reducing, fuel cells are assembled and their operation compared in pseudo-physiological buffer. A selected fuel cell is also tested for operation in artificial plasma, containing interferents present under physiological conditions. The maximum power density observed for the selected fuel cell based on glucose dehydrogenase and Myceliophthora thermophila laccase enzyme electrodes as anode and cathode, respectively, decreases from 110 micro W /cm^2 in buffer to 60 micro W /cm^2 on testing in artificial plasma. This EFC provides the highest power density output reported to date for a fully enzymatic glucoseoxidising, oxygen-reducing fuel cell operating in artificial plasma.
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