Cu-CDs/H2O2 system with peroxidase-like activities at neutral pH for the co-catalytic oxidation of o-phenylenediamine and inhibition of catalytic activity by Cr(III)

The construction of highly efficient nanozyme activities in a simple means is vital for the wide biological and chemical applications. Present work describes a Cu-based carbon dots (Cu-CDs) with oxidase- and peroxidase-like activity for the catalytic oxidation of o-phenylenediamine (OPD) at neutral pH. The peroxidase-like activity of Cu-CDs was finely tuned and enhanced by changing the ascorbic acid (AA) content and reduction temperature to increase the Cu+ content. The oxidation of OPD was significantly accelerated by the addition of Fe2+ ions (i.e., Cu-CDs + Fe2+/H2O2 system) and presented a smaller Km (Michaelis constant) and a higher Vmax (maximum rate) than horseradish peroxidase (HRP) at the same mass concentration. The Cu-CDs with oxidase- and peroxidase-like activities could catalyze to produce the superoxide radical (·O2-) and hydroxyl radical (·OH) in the system. Interestingly, the catalytic oxidation of OPD to 2,3-diaminophenazine (DAP) could be inhibited by Cr(III) ions in Cu-CDs + Fe2+/H2O2 system. Therefore, a new fluorescent detection strategy was developed for the detection of Cr(III) with the linear range of 0.2−100 μM, and the detection limit of 36 nM (S/N = 3). This work provides new insight into the mechanism and kinetics of low-valence copper–carbon dots peroxidase-like and Fenton co-catalyst system.