A New Amperometric Glucose Sensor Based on Bilayer Film Coating of Redox-Active Clay Film and Glucose Oxidase Enzyme Film

A new amperometric glucose sensor based on bilayer film coating has been fabricated and its sensor characteristics under a steady-state condition have been examined. The electrode substrate was coated with two kinds of polymer films in a bilayer state, i.e., first with the redox-active montmorillonite clay film into which [Ru(NH3)6]3+ complexes are incorporated electrostatically and they function as an electron shuttle which delivers electrons to redox-active sites in the clay film, and then with the enzyme film consisting of bovine serum albumin and glucose oxidase (GOx). The glucose concentration could be monitored by measuring the current for H2O2 reduction electrocatalyzed by the inner clay film where H2O2 was produced by the glucose–GOx enzyme reaction in the outer enzyme film. The mechanism of the overall electrode/enzyme reaction for this amperometric glucose sensor is represented as follows: (Remark: Graphics omitted.) where reactions 1,2,3, and 4 correspond to the glucose–glucose oxidase enzyme reaction, the hydrolysis reaction of d-glucono-δ-lactone, the electrocatalytic reduction of H2O2 by the montmorillonite clay containing [Ru(NH3)6]2+ and the electrode reaction of the [Ru(NH3)6]2+⁄3+ couple, respectively. The reproducible relationship between glucose concentration and sensor output was obtained. The sensitivity and the dynamic range were found to depend on the amount of GOx confined in the enzyme film and its thickness.