Hydrogen peroxide biosensor based on direct electrochemistry of soybean peroxidase immobilized on single-walled carbon nanohorn modified electrode

Single-walled carbon nanohorns (SWCNHs) were used as a novel and biocompatible matrix for fabricating biosensing devices. The direct immobilization of acid-stable and thermostable soybean peroxidase (SBP) on SWCNH modified electrode surface can realize the direct electrochemistry of enzyme. Cyclic voltammogram of the adsorbed SBP displays a pair of redox peaks with a formal potential of −0.24 V in pH 5 phosphate buffer solution. The formal potential has a linear relationship with pH from 3 to 9 with a slope of −48.7 mV/pH, close to the value of −55.7 mV/pH expected at 18 °C for the reversible transfer of one proton and one electron. Bioactivity of SBP remains good in SWCNH microenvironment, along with effective catalysis of the reduction of H2O2. In the absence of a mediator, this H2O2 biosensor exhibited a high sensitivity (16.625 μA L/mmol), a linear range from 0.02 to 1.2 mmol L−1, and a detection limit of 5.0 × 10−7 mmol L−1, as well as acceptable preparation reproducibility and excellent stability.