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 (k_s) was 3.82 s^-1. The HRP/TiO₂ NTAs modified electrode displayed an excellent electrocatalytic performance for H₂O₂ and the formal Michaelis-Menten constant (K_m^app) 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.