Direct electrochemistry and enhanced electrocatalysis of horseradish peroxidase based on flowerlike ZnO-gold nanoparticle-Nafion nanocomposite

We developed a new flowerlike ZnO-gold nanoparticles (GNPs)-Nafion nanocomposite which can promote the direct electron transfer of horseradish peroxidase (HRP) immobilized in the film effectively. The cyclic voltammetric results show that HRP entrapped in the composite could undergo a direct quasi-reversible electrochemical reaction with a formal potential (E-0') of -0.32V (versus Ag/AgCl) in phosphate buffer solution (PBS). The flowerlike ZnO and GNPs show synergistic effect and the ZnO-GNPs-Nafion-HRP modified GC electrode gives an enhanced electrocatalytic activity towards the reduction of hydrogen peroxide (H2O2). The calculated apparent Michaelis-Menten constant (K-m(app)) is M 1.76 mM. which is much lower than that reported, indicating a high catalytic activity of HRP. The catalysis currents increase linearly to the H2O2 concentration in a wide range of 1.5 x 10(-5) to 1.1 X 10(-3) M, with a correlation coefficient of 0.998. The detection limit is 9.0 x 10(-6) M (at the ratio of signal to noise, S/N = 3), demonstrating that the formed film provides a favorable microenvironment for the enzyme to retain its activity. Moreover, the modified electrode displays rapid response to H2O2 and possesses good stability and reproducibility. (C) 2008 Elsevier B.V. All rights reserved.