An insight into the mechanism of peroxidase-like activity of carbon dots

The interest in carbon dots (CDs) as peroxidase-mimics has urged to understand the mechanism for this reaction of commercial importance. Firstly, using a theoretical-cum-experimental approach, the –COOH group was identified as an active moiety for strongly binding and degrading H2O2 in the presence of a reducing equivalent. Next, the stringency of different compounds containing the –COOH group was examined and identified l-glutamic acid with higher peroxidase-like activity. The –NH2 group present in the vicinity of the –COOH group increased the activity of l-glutamic acid. Following a pyrolysis method, l-glutamic acid was transformed into CDs having a diameter of 3.18 ± 0.53 nm with its core made of pyroglutamic acid. The CD exhibited thermostability (~90 °C) and higher peroxidase-like activity than the l-glutamic acid. The higher activity of the CD was attributed to its binding affinity with ABTS and H2O2. The Km and Kcat of the CD for H2O2 were 5.85 mM and 0.011 s−1, respectively. Based on spectroscopic investigations, we confirmed the peroxidase-like activity is a surface phenomenon that did not have a significant link to the photophysical property of the CD and proposed a mechanism for the reaction. The colorimetric reaction could be reproduced on a paper platform, confirming the application potential of the CD for developing a low-cost peroxide sensor.