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

Gold nano-seeds (GNSs) (Ф = 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 microenvironment 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–GNSs–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 × 10 −5 to 6.3 × 10 −4 mol L−1, with a detection limit of 5.9 × 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.