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 M -1 s -1 to 2.1 × 10 4 M -1 s -1 for water -acetonitrile solutions containing 5 % to 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-immobilized 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 1.0 mM 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 2 displays excellent electrochemical catalytic activities even when immobilised on the surface of the electrode. Highlights: The kinetics of the electrocatalytic oxidation of glucose with GOx mediated by a new electron shuttling mediator, PTZ, was studied. PTZ delivers superior potential performance among azine-type redox mediators for GOx. PTZ and GOx, LOx and ChOx were successfully co-immobilized in sol-gel membrane on a screen-printed electrode to construct glucose, lactate and cholesterol biosensors, respectively. Second-order rate constants for the reaction between the mediator and variety of oxidases co-immobilised inside a sol-gel membrane were obtained by chronoamperometry.

Application of Polyfolates in the Development of Electrochemical Glucose Biosensors

“…Nevertheless, a few biosensors with phenazine‐group mediators operated also at positive potentials, e.g. at +0.2 V vs. Ag/AgCl 34 or SCE 35, biosensor modified with methylene green or phenazine methosulfate 34, and GDH/PMB/Au biosensor 35, where GDH is glucose dehydrogenase; and at +0.3 V vs. Ag/AgCl biosensor mediated with phenothiazine 36. Majority of glucose biosensors were operating in fixed potential chronoamperometry, however, differential pulse voltammetry was also used with GOx/PMB‐SiO 2 ‐NP/GCE 37.…”

“…Majority of glucose biosensors were operating in fixed potential chronoamperometry, however, differential pulse voltammetry was also used with GOx/PMB‐SiO 2 ‐NP/GCE 37. The linear dynamic ranges reported were up 0.9 mmol L −1 17 as the shortest and up to 32 mmol L −1 36 as the longest. The linear range also depended on oxygen presence in solution being larger in the presence of oxygen as was found for some biosensors based on phenazine type monomers as mediators 34.…”

Conducting Polymers as Elements of Miniature Biocompatible Sensor

“…Classically, the distance among the active centre of the enzyme and the electrode surface is too long for direct electron transfer (DET) owing to the protective disk of the enzyme. Because electron transfer (ET) via a tunneling mechanism is rarely observed in classic electrodes, establishing electron relays that allow for fast ET, thus avoiding free-diffusing redox species between the electrode and the enzyme, is vital [35]. Due to the fact, organic electronic materials present very attractive expectants for molecular wiring owing to their polymeric essence and conducting character [36].…”

Facilitating electron transfer in bioelectrocatalytic systems

“…In the latter case, a so-called "reagentless architecture" of the bioelectrocatalytic system is realised. To estimate the efficiency of the ET in heterogeneous systems, rotating disk voltammetry, 61,62 , cyclic voltammetry 63,64 or chronoamperometry 65,66 can be used (sections 6.2.6, 6.2.3 and 6.2.5, respectively).…”