Towards improved performance of mediated glucose oxidising enzyme electrodes for biosensing and biopower applications
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2019-11Author
Bennett, Richard W.
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Abstract
Energy produced through enzymatic catalysis at electrodes, namely oxidation of glucose and
reduction of oxygen may be used to power devices. The goal of powering implantable or semiimplantable
medical devices through enzymes has driven forward the field of enzymatic
bioelectrochemistry. Significant challenges must be overcome prior to their inclusion as a
power source for medical devices such as low power output, poor operational stabilities and
biocompatibility issues. Similar challenges hinder the development of continuous use
enzymatic biosensors with poor operational stabilities and biocompatibility preventing long
term deployment. This thesis aims to build on work carried out previously in the area of enzyme
electrode assembly for fuel cell and biosensor development to improve the understanding and
performance of glucose oxidising enzyme electrodes for enhanced operation. Novel enzyme
electrode immobilisation strategies are investigated and compared with previously published
enzyme electrode assemblies. Enzyme electrodes were prepared using the
electropolymerisation of L-Dopa to poly(L-Dopa) as an immobilisation strategy. Improved
optimisation methodologies are reported and used to assemble glucose oxidising electrodes
with higher current output than those previously described.Enzyme electrodes consisting of
co-immobilised redox polymer with FADGDH, MWCNTs and PEGDGE achieved current
densities of 1.22 ± 0.10 mA cm-2 in PBS containing 5 mM glucose were achieved, 52 % higher
than those using one factor at a time optimisation approaches. Enzyme electrodes consisting of
co-immobilised redox polymer with FADGDH, MWCNTs and PEGDGE were tested in test
solutions containing individual plasma components to investigate the reduced performance of
enzyme electrodes in human physiological solutions. Electrodes tested in the presence of uric
acid generated the lowest current responses and the lowest operational stabilities of all
individual plasma components. Current densities of 0.9 ± 0.10 mA cm-2 were observed at 5
mM glucose concentrations in the presence of uric acid compared to 1.5 ± 0.10 mA cm-2 in
PBS with no uric acid present. 46 % of the initial current remained after 12 hours continuous
operation in the presence of uric acid compared to 72 % for PBS with no uric acid present. In
comparison, glucose oxidase based electrodes maintained identical operational stabilities of 70
% with and without uric acid present while cellobiose dehydrogenase electrodes maintained 86
% stability in PBS, with 33 % stability in the presence of uric acid. Enzyme electrodes were
prepared with Nafion coatings to minimise the effect of plasma on the enzymatic film. Current
densities of 8.0 ± 2.0 mA cm-2 were recorded in 100 mM for glucose oxidase enzyme electrodes
prepared with a 0.5 % w/v Nafion coating with an operational stability of 84 % for 12-hour
continuous operation when tested in artificial plasma. FADGDH based electrodes in the same
test conditions produced current densities of 4.5 ± 0.70 mA cm-2 and an operational stability of
58 %. Further work is required to fully understand changes to enzyme electrode performance
in physiological solutions and strategies to minimise the impact of these solutions for operation
in-vivo to allow for higher power outputs and longer operational lifetimes for prototype
devices.