Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase based on gold nano-seeds dotted TiO2 nanocomposite

Gold nano-seeds (GNSs) (Phi = 2-5 nm) were dotted in TiO2 colloids and the horseradish peroxidase (HRP) was successfully immobilized on the as-made GNSs-TiO2 nanocomposite by a convenient and effective method. The matrix integrates the merits of both GNSs and TiO2, which provides a favorable micro-environment for the immobilization of HRP. The cyclic votammetric results demonstrated that the entrapped HRP achieves direct electron transfer at glassy carbon electrode (GCE). A pair of stable and quasi-reversible redox peaks with a small peak-to-peak separation of 43 mV was observed in phosphate buffer solution. The GNSs stabilized by TiO2 colloids acted sufficiently as the conducting tunnel to promote the electron transfer. As a result, the electrochemical behaviors were improved in virtue of the synergic effect of TiO2 and GNSs. The Nafion/HRP-GNS5-TiO2/GCE displayed an excellent and rapid electrocatalytic response to the reduction of H2O2. The proposed biosensor exhibited a good linear response in the range from 4.1 x 10(-5) to 6.3 x 10(-4) mol L-1, with a detection limit of 5.9 x 10(-6) mol L-1 (at the ration of signal to noise, S/N = 3). The apparent Michaelis-Menten constant was estimated to be 0.63 mmol L-1 Furthermore, the biosensor possesses satisfactory stability and good reproducibility. (C) 2010 Elsevier B.V. All rights reserved.