Direct electrochemistry and electrocatalysis of horseradish peroxidase in MnO2 nanosheet film

A novel material MnO₂ nanosheet has been used as the support matrix for the immobilization of horseradish peroxidase (HRP). HRP entrapped in MnO₂ nanosheet film exhibits facile direct electron transfer with the electron transfer rate constant of 6.86 s⁻¹. The HRP/MnO₂ nanosheet film gives a reversible redox couple with the apparent formal peak potential (E ⁰) of −0.315 V (vs. Ag/AgCl) in pH 6.5 phosphate buffer solution (PBS). The formal potential E ⁰ of HRP shifts linearly with pH with a slope of −53.75 mV · pH⁻¹, denoting that an electron transfer accompanies single-proton transportation. The immobilized HRP shows an electrocatalytic activity to the reduction of H₂O₂. The response time of the biosensor for H₂O₂ is less than 3 s, and the detection limit is 0.21 μmol · L⁻¹ based on signal/noise = 3. Supported by the National Natural Science Foundation of China (Grant No. 20301002) and the National 863 Program of China (Grant No. 2006AA03Z343)