Direct electrochemistry of horseradish peroxidase on TiO2 nanotube arrays via seeded-growth synthesis

Horseradish peroxidase (HRP) was successfully immobilized on vertically oriented TiO2 nanotube arrays (NTAs), which was prepared by a seeded-growth mechanism. The nanotubular structure of TiO2 was characterized by scanning electron microscope (SEM). After encapsulated HRP on TiO2 nanotube arrays, the direct electron transfer of HRP was observed. Owing to the redox reaction of electroactive center of HRP, the HRP/TiO2 NTAs modified electrode exhibited a pair of quasi-reversible peaks with the peak-to-peak separation of 70 mV and the formal potential of −0.122 V (vs. SCE) in 0.2 mol L−1 phosphate buffer solution (PBS, pH 7.0). The number of transference electron was 0.84 and the direct electron transfer (ET) constant (ks) was 3.82 s−1. The HRP/TiO2 NTAs modified electrode displayed an excellent electrocatalytic performance for H2O2 and the formal Michaelis–Menten constant (Kmapp) was 1.9 mmol L−1. The response currents had a good linear relation with the concentration of H2O2 from 5.0 × 10−7 mol L−1 to 1.0 × 10−5 mol L−1 and 5.0 × 10−5 mol L−1 to 1.0 × 10−3 mol L−1, respectively.