title: Dynamic and steady state 1-D model of mediated electron transfer in a porous enzymatic electrode.
abstract: A 1-D mathematical model of a porous enzymatic electrode exhibiting the mediated electron transfer (MET) mechanism has been developed. As a model system, glucose oxidation catalyzed by immobilized glucose oxidase (GOx) in the presence of a co-immobilized tetrathiafulvalene (TTF) mediator in the porous electrode matrix has been selected. The balance equations for potential fields in the electron- and ion-conducting phases as well as concentration field have been formulated, solved numerically and validated experimentally under steady state conditions. The relevant kinetic parameters of the lumped reaction kinetics have been obtained by global optimization. The confidence intervals (CIs) of each parameter have been extracted from the respective likelihood. The parameter study has shown that the parameters related to mediator consumption/regeneration steps can be responsible for the shift of the reaction onset potential. Additionally, the model has shown that diffusion of the oxidized mediator out of the catalyst layer (CL) plays a significant role only at more positive potentials and low glucose concentrations. Only concentration profiles in different layers influence the electrode performance while other state fields like potential distributions in different phases have no impact on the performance. The concentration profiles reveal that all electrodes work through; the observed limiting currents are diffusion-reaction limiting. The normalized electrode activity decreases with an increase of enzyme loading. According to the model, the reason for this observation is glucose depletion along the CL at higher enzyme loadings. Comparison with experiments advices a decrease of enzyme utilization at higher enzyme loadings.
authors.affiliation: Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstraße 1, D-39106 Magdeburg, Germany.
authors.forename: T Q N
authors.initials: TQ
authors.lastname: Do
authors.affiliation: Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstraße 1, D-39106 Magdeburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Varničić
authors.affiliation: Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstraße 1, D-39106 Magdeburg, Germany.
authors.forename: R J
authors.initials: RJ
authors.lastname: Flassig
authors.affiliation: Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstraße 1, D-39106 Magdeburg, Germany. Electronic address: vidakovic@mpi-magdeburg.mpg.de.
authors.forename: T
authors.initials: T
authors.lastname: Vidaković-Koch
authors.affiliation: Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstraße 1, D-39106 Magdeburg, Germany; Otto-von-Guericke University Magdeburg, Process Systems Engineering, Universitätsplatz 2, D-39106 Magdeburg, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Sundmacher
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology; D055162:Biocatalysis; D004563:Electrochemistry; D004566:Electrodes; D004579:Electron Transport; D004800:Enzymes, Immobilized / Q000737:chemistry / Q000378:metabolism; D005947:Glucose / Q000737:chemistry; D005949:Glucose Oxidase / Q000737:chemistry* / Q000378:metabolism*; D006571:Heterocyclic Compounds / Q000737:chemistry; D008956:Models, Chemical; D016062:Porosity
chemical_list: D004800:Enzymes, Immobilized; D006571:Heterocyclic Compounds; D005949:Glucose Oxidase; C063887:tetrathiafulvalene; D005947:Glucose
keywords: Glucose oxidase (GOx); Kinetic parameters; Mediated electron transfer (MET); Porous enzymatic electrode model; Tetrathiafulvalene (TTF)