title: Unsubstituted phenothiazine as a superior water-insoluble mediator for oxidases.
abstract: The mediation of oxidases glucose oxidase (GOx), lactate oxidase (LOx) and cholesterol oxidase (ChOx) by a new electron shuttling mediator, unsubstituted phenothiazine (PTZ), was studied. Cyclic voltammetry and rotating-disk electrode measurements in nonaqueous media were used to determine the diffusion characteristics of the mediator and the kinetics of its reaction with GOx, giving a second-order rate constant of 7.6 × 10(3)-2.1 × 10(4)M(-1)s(-1) for water-acetonitrile solutions containing 5-15% water. These values are in the range reported for commonly used azine-type mediators, indicating that PTZ is able to function as an efficient mediator. PTZ and GOx, LOx and ChOx were successfully co-immobilised in sol-gel membrane on a screen-printed electrode to construct glucose, lactate and cholesterol biosensors, respectively, which were then optimised in terms of stability and sensitivity. The electrocatalytic oxidation responses showed a dependence on substrate concentration ranging from 0.6 to 32 mM for glucose, from 19 to 565 mM for lactate and from 0.015 to 1.0mM for cholesterol detection. Oxidation of substrates on the surface of electrodes modified with PTZ and enzyme membrane was investigated with double-step chronoamperometry and the results showed that the PTZ displays excellent electrochemical catalytic activities even when immobilised on the surface of the electrode.
authors.affiliation: Faculty of Chemistry, M.V. Lomonosov Moscow State University, Lenin's Hills, 119991 Moscow, Russia; Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Alina N
authors.initials: AN
authors.lastname: Sekretaryova
authors.forename: Mikhail Yu
authors.initials: MY
authors.lastname: Vagin
authors.forename: Valerio
authors.initials: V
authors.lastname: Beni
authors.forename: Anthony P F
authors.initials: AP
authors.lastname: Turner
authors.forename: Arkady A
authors.initials: AA
authors.lastname: Karyakin
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D002784:Cholesterol / Q000737:chemistry / Q000302:isolation & purification*; D002789:Cholesterol Oxidase / Q000737:chemistry; D004800:Enzymes, Immobilized; D005947:Glucose / Q000737:chemistry / Q000302:isolation & purification*; D005949:Glucose Oxidase / Q000737:chemistry; D006801:Humans; D019344:Lactic Acid / Q000737:chemistry / Q000302:isolation & purification*; D006899:Mixed Function Oxygenases / Q000737:chemistry; D010084:Oxidation-Reduction; D010640:Phenothiazines / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D004800:Enzymes, Immobilized; D010640:Phenothiazines; D014867:Water; D019344:Lactic Acid; D002784:Cholesterol; D006899:Mixed Function Oxygenases; D005949:Glucose Oxidase; D002789:Cholesterol Oxidase; C021497:lactate 2-monooxygenase; C031637:phenothiazine; D005947:Glucose
keywords: Cholesterol oxidase; Electron transfer mediator; Enzyme biosensor; Glucose oxidase; Lactate oxidase; Phenothiazine