In situ synthesized gold nanoparticles for direct electrochemistry of horseradish peroxidase

In order to construct a three-dimensional electrode, in situ electrochemical deposition of gold nanoparticles onto a gold electrode coated with a self-assembled monolayer of 3-mercaptopropionic acid (Au NP/MPA/Au) was conducted. Horseradish peroxidase (HRP) was then immobilized into this three-dimensional electrode, leading to the realization of direct electron transfer of HRP. Scanning electron microscopy and electrochemical impedance spectroscopy were applied to characterize the electrode before and after HRP immobilization. The apparent Michaelis-Menten constant for immobilized HRP on a Au NP/MPA/Au electrode is 0.78 mM, indicating high enzymatic activity of HRP. The HRP modified electrode was further utilized as a sensing platform for the electrocatalytic reduction and detection of hydrogen peroxide. For the detection of hydrogen peroxide on this electrode, the sensitivity is 311.72 μA mM−1 cm−2, the detection limit is 0.16 μM, and the dynamic range is from 0.48 μM to 1.2 mM. Therefore this electrode is a promising device for sensitive and reproducible detection of H2O2.