Choline biosensors based on a bi-electrocatalytic property of MnO2 nanoparticles modified electrodes to H2O2

An interesting mode of reactivity of MnO2 nanoparticles modified electrode in the presence of H2O2 is reported. The MnO2 nanoparticles modified electrodes show a bi-direction electrocatalytic ability toward the reduction/oxidation of H2O2. Based on this property, a choline biosensor was fabricated via a direct and facile electrochemical deposition of a biocomposite that was made of chitosan hydrogel, choline oxidase (ChOx) and MnO2 nanoparticles onto a glassy carbon (GC electrode. The biocomposite is homogeneous and easily prepared and provides a shelter for the enzyme to retain its bioactivity. The results of square wave voltammetry showed that the electrocatalytic reduction currents increased linearly with the increase of choline chloride concentration in the range of 1.0 X 10(-5) - 2.1 X 10(-3) M and no obvious interference from ascorbic acid and uric acid was observed. Good reproducibility and stability were obtained. A possible reaction mechanism was proposed. (C) 2007 Elsevier B.V. All rights reserved.