For colorimetric detection using the HRP-catalyzed reaction, the concentration of H2O2 is an important parameter for achieving reliable results. If the concentration of H2O2 is too high, it may lead to background oxidation. On the other hand, a too low concentration of H2O2 will not be able to convert TMB into oxidized form to generate the visible signal. Fig. shows that with the H2O2 concentration increased from 0.05 mM to 0.5 mM, the absorbance value increased in proportion. When the H2O2 concentration increased from 0.25 mM to 0.5 mM, the absorbance value remains almost unchanged. Therefore, we choose 0.25 mM as the optimal concentration of H2O2 in all subsequent experiments. The reaction time of the colorimetric system was varied to find out the most suitable condition. The HRP-catalyzed reaction was carried out for different periods before the reaction was stopped. In Fig. , it shows that from 4 to 10 min, the absorbance value continued to increase. After 10 min reaction, the absorbance did not increase any further. Therefore, we chose 10 min as the reaction time in the final colorimetric assay.