Electrochemical properties of violuric acid and oxidase biosensor preparation

The electrochemical properties of violuric acid (VA) have been investigated at pH 4.0¯10.0 by using cyclic voltammetry on a glassy carbon electrode. The peak current was proportional to the square root of the potential scan rate. The calculated diffusion coefficient was 2.0±0.7×10-6 cm2 s-1. The formal oxidation¯reduction potential of VA was 0.63 V versus SCE at pH 7.0. The kinetics of VA interaction with reduced glucose oxidase (GO) was explored in the electrocatalytical system. A typical electrocatalytical wave was generated in the presence of the VA and glucose. An apparent kox calculated by using the Nicholson¯Shain function was 1.85×106 M-1 s-1 at pH 7.0 and 25 °C. Glucose and -lactate bioelectrodes were prepared by adsorbing the GO and -lactate oxidase (LO) onto the VA-modified graphite electrode. The electrode was poised at 0.6 V versus SCE and linear response was obtained over the range of 4¯20 mM glucose and 2_12 mM -lactate, respectively.