Development and kinetic characterization of hierarchical bioelectrocatalytic system utilizing a redox mediator, functionalized carbon nanotubes and an enzyme for glucose oxidation

Abstract A multifunctional bioelectrocatalytic material that permits shifting the onset potential for the oxidation of glucose to the value starting below −0.2 V (vs. Ag/AgCl) is described. It includes carbon nanotubes modified with 4‑(pyrrole‑1‑yl) benzoic acid, which introduces carboxyl groups that play an important role in enzyme (glucose oxidase) immobilization and improve the stability of the system. Glucose oxidase has been immobilized by a chemical crosslinking method, where bovine serum albumin and glutaraldehyde are used as a blocking and a crosslinking agent, respectively. Here N -methylphenazonium methyl sulfate has been considered as co-catalyst and a component of the redox mediating system facilitating the effective flow of electrons from redox centers of the enzyme to the electrode surface at fairly negative potentials. The mediator has been confined to the system by the electrostatic attraction with the sulfonate groups of Nafion. Dynamics of charge propagation in the proposed hybrid bioelectrocatalytic films have been assessed from chronocoulometric measurements. The combination of carbon nanotubes, glucose oxidase and N -methylphenazonium methyl sulfate produces a system that is capable of effective oxidation of glucose in 0.1 mol dm −3 phosphate buffer solution at pH 7.0. It can be concluded on the basis of various biochemical and electroanalytical approaches that the system is well-behaved, stable, and redox facile. The Michaelis-Menten constant and the maximum current density (measured in the glucose-containing solutions) are 18 mmol dm −3 and 0.32 mA cm −2 , respectively. By referring to fundamentals of electrochemical kinetic analysis, the rate constant in heterogeneous units, 5 ∗ 10 −5  cm s −1 , has been determined. The calibration plot has a linear response range for glucose concentrations up to ca. 10–12 mmol dm −3 (sensitivity, 12.1 μA mmol −1  dm 3  cm −2 ). An observation of importance to the biofuel cell technology is the appearance of the glucose oxidation voltammetric peak at fairly negative potentials, namely ca. −0.05 V (vs. Ag/AgCl).