Cascade selective recognition of H2O2 and ascorbic acid in living cells using carbon-based nanozymes with peroxidase-like activity

The design of optical nanosensors based on carbon nanozymes has gained considerable interest in analyte detection. In this study, a simple and rapid fluorescence/colorimetry probe, NH2GQDs/o-phenylenediamine (OPD), was constructed by combining amino-functionalized graphene quantum dots (NH2GQDs) and o-phe-nylenediamine. In the presence of NH2GQDs/H2O2, OPD was oxidized to 2,3-diaminophenazine (DAP), giving fluorescent and colorimetric signals, which can be used to quantitatively measure H2O2. Furthermore, NH2GQDs/OPD/ H2O2 exhibited high selectivity and sensitivity for detecting ascorbic acid (AA) with a detection limit of 0.062 mu M using the fluorescent method. Its selectivity for AA was ascribed to the formation of the condensation compound of DAP with dehydroascorbic acid rather than the quinoxaline path for dopamine and glucose. The colorimetric sensing system NH2GQDs/OPD displayed yellow in the presence of H2O2, while it changed to green upon adding AA. This sensing system was successfully applied for imaging H2O2 and AA in human cervical cancer cells and onion tissues. Additionally, the flexible sensing system can be used to fabricate the logic gate "AND." The results provide a valuable method for its potential application in the biosensing, clinical medicine, and food industries.