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 (similar to 90 degrees 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 K-m and K-cat 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.