Gold foil-based biosensor for the determination of hydrogen peroxide.

Hydrogen peroxide ($\text{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$) plays a critical role in the regulation of multifarious physiological processes. We developed a sensor containing a mercaptopropionic acid (MPA) monolayer covalently immobilized with Horseradish peroxidase (HRP) enzyme for the electrochemical detection of hydrogen peroxide ($\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$). A gold foil substrate was chemically treated with nitric acid and were used as working electrode. Platinum wire and Ag-Ag/Cl were used as counter and reference electrodes, respectively. The acid treated gold electrode with the immobilized enzyme shown to have improved catalytic activity in the reduction of $\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$. The steady-state current response increases linearly with $\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$ concentration from 10 $\mu \textbf{M}$ to 9 mM with a low detection limit of 60 $\mu \textbf{M}$ and showed a sensitivity of 0.4 mA/ mM cm$^{\mathbf {2}}$. This electrochemical sensor is demonstrated to be highly selective and sensitive in the presence of interfering analytes. The improved activity and simple preparation method of the electrode makes the MPAHRP modified gold electrode promising for being developed as an attractive robust material for electrochemical $\textbf{H}_{\mathbf {2}} \mathbf {O} _{\mathbf {2}}$ sensing.