Direct electrochemistry of horseradish peroxidase at a carbon nanotube electrode

Horseradish peroxidase (HRP) immobilized on the surface of the carbon nanotube modified glassy carbon electrode (HRP-CNT/GC) can undergo effective and stable direct electron transfer reaction. The cyclic voltammetric results indicate that the HRP-CNT/GC electrode exhibits a pair of well-defined and nearly symmetrical redox peaks in 0.1 mol/L phosphate buffer solution. Its formal redox potential, E-0', is almost independent on the scan rates, the average value of E-0' is (-0.319 +/- 0.002) V (vs. SCE, pH 6.9) in the phosphate buffer solution (pH 6.9) in the scan rate range of 20 similar to 100 mV/s. The dependence of E-0' on the pH of the buffer solution indicates that the direct electron transfer of HRP is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized HRP retained its bioelectrocatalytic activity for the reduction of H2O2 and the HRP-CNT/GC electrode can rapidly respond to the change of the concentration of H2O2. The method presented here can be easily extended to obtain the direct electrochemistry of other redox enzymes or proteins.