and reduction peak currents on contact times between H2O2 and HRP
was shown in Fig. 5b. For both oxidation and reduction, a significant decrease
of the peak currents was observed from 0 to 5 min then saturated,
suggesting that the optimum contact time is between 0 and 5 min.
Furthermore, as it is known that enzymatic reaction is strongly affected
by pH condition, the dependence of the peak currents on pH was also
examined. Fig. 5c shows the pH dependence in the pH range of 6.8–
7.4 in 0.1 M PBS solution containing 100 mU HRP and 20 mM H2O2
after a contact time of 5 min. Small increase of both oxidation–reduction
peak currents was found from pH 6.8 to pH 7.0 and then saturated.
Based on the result, pH 7.0 was used for the next experiments.