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Mediated Electron Transfer at Redox Active Monolayers. Part 4: Kinetics of Redox Enzymes Coupled With Electron Mediators
Physical Electrochemistry Laboratory, Department of Chemistry, Nasr Institute of Advanced Materials Science, University of Dublin, Trinity College, Dublin 2, Ireland
Received: 20 December 2002; Accepted: 6 January 2003 / Published: 26 January 2003
Abstract: A detailed kinetic analysis of the pertinent physical processes underlying the operation of enzyme electrodes immobilized within alkane thiol self assembled monolayers is developed. These electrodes utilize a soluble mediator, which partitions into the monolayer, regenerates the active catalytic form of the enzyme and is re-oxidized at the underlying support electrode surface giving rise to a current which reflects kinetic events at the enzyme surface. Both the enzyme/substrate and enzyme mediator kinetics have been quantified fully in terms of a ping-pong mechanism for the former and Michaelis-Menten kinetics for the latter. The effect of substrate and mediator diffusion in solution have also been specifically considered and the latter processes have been shown to result in a complex expression for the reaction flux. Four limiting kinetic cases have been enumerated and simple expressions for the reaction flux in each of these rate limiting situations have been developed. Kinetic case diagrams have been presented as an aid to mechanistic diagnosis. The complicating effects of diffusive loss of reduced mediator from the enzyme layer have also been examined and the relation between the observed flux corresponding to reduced mediator oxidation at the support electrode and the substrate reaction flux in the enzyme layer have been quantified in terms of an efficiency factor. Results extracted from recently published practical realizations of immobilized monolayer enzyme systems have been discussed in the context of the proposed model analysis.
Keywords: Amperometric enzyme electrodes; Alkane thiol monolayers; Immobilized glucose oxidase biosensors; Enzyme kinetics; Theory of electrochemical enzyme electrodes
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Lyons, M.E. Mediated Electron Transfer at Redox Active Monolayers. Part 4: Kinetics of Redox Enzymes Coupled With Electron Mediators. Sensors 2003, 3, 19-42.
Lyons ME. Mediated Electron Transfer at Redox Active Monolayers. Part 4: Kinetics of Redox Enzymes Coupled With Electron Mediators. Sensors. 2003; 3(2):19-42.
Lyons, Michael E. 2003. "Mediated Electron Transfer at Redox Active Monolayers. Part 4: Kinetics of Redox Enzymes Coupled With Electron Mediators." Sensors 3, no. 2: 19-42.