title: Bioelectrocatalytic detection of theophylline at theophylline oxidase electrodes.
abstract: Bioelectrocatalytic oxidation of theophylline was studied at gold and graphite electrodes modified with microbial theophylline oxidase (ThOx), a multi-cofactor redox enzyme capable of selective oxidation of theophylline. Gold electrodes were additionally modified with self-assembled monolayers (SAMs) of (-OH)- and (-NH(2))-terminated alkanethiols of different chain lengths, to achieve compatibility between ThOx and the electrode surface. On graphite, ThOx was either physically co-adsorbed with a surfactant didodecyldimethylammonium bromide (DDAB), or entrapped within an Os-redox-polymer film. At all electrodes, ThOx was bioelectrocatalytically active; direct electrochemistry of ThOx in the absence of theophylline was followed only at the SAM-modified gold electrodes. Direct electrochemistry of ThOx correlated with redox transformations of the heme domain of ThOx, with a E(o/)of -110+/-2 mV versus Ag|AgCl, at pH 7. Bioelectrocatalytic oxidation of theophylline was optimal at mixed (-OH)/(-NH(2))-terminated SAMs; co-adsorption of ThOx with DDAB improved the bioelectrocatalytic performance of the ThOx-electrode. In both cases, the response to theophylline was within the mM range. Alternatively, a reagentless ThOx-electrode based on ThOx cross-linked within the Os-redox-polymer matrix demonstrated a linear response to theophylline within the physiologically important 0.02-0.6mM (3.6-72 mg l(-1)) concentration range with a sensitivity of 52.1+/-7.8 mA cm(-2)M(-1).
authors.affiliation: School of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK. elena.ferapontova@ed.ac.uk <elena.ferapontova@ed.ac.uk>
authors.forename: Elena E
authors.initials: EE
authors.lastname: Ferapontova
authors.forename: Stepan
authors.initials: S
authors.lastname: Shipovskov
authors.forename: Lo
authors.initials: L
authors.lastname: Gorton
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation / Q000379:methods*; D002384:Catalysis; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D004563:Electrochemistry / Q000295:instrumentation / Q000379:methods*; D004800:Enzymes, Immobilized / Q000737:chemistry; D008839:Microelectrodes; D010088:Oxidoreductases / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013806:Theophylline / Q000032:analysis* / Q000737:chemistry
chemical_list: D020099:Coated Materials, Biocompatible; D004800:Enzymes, Immobilized; D013806:Theophylline; D010088:Oxidoreductases; C073406:theophylline oxidase