The electrochemical behavior of Mel was examined in
H2SO4 with different concentration. As shown in Fig. 7, the
oxidation–redox peak current of Mel climbed then dropped when
the concentration of H2SO4 was higher than 0.5 M, which agrees
that Mel will be hydrolyzed in strong acid condition by gradually
replacing amino groups into hydroxyl groups [46]. To achieve high
sensitivity and better oxidation peak, the 0.5 M H2SO4 was used for
the experiment.