Ultrasensitive pH-switchablenitrogen doped carbon dots for MnO₄^- detection and fluorescent anti-counterfeiting

Herein, high-efficiency green fluorescence nitrogen doped CDs (G-CDs) were prepared using acetaminophen and ethylenediamine as precursors. The G-CDs exhibited good anti-photobleaching, salttolerance and low cytotoxicity. Interestingly, the G-CDs revealed excellent fluorescence stability in the pH range of 6-12, however, the intensity of the G-CDs was almost completely quenched in other pH values. The MnO₄^- demonstrated strong fluorescence quenching capability on our G-CDs with the mechanism involving dynamic quenching caused by energy transfer. G-CDs exhibited a strong linear relationship with MnO₄^- concentration in the range of 0-75 μmol/L, with a low limit detection of 7.6 nmol/L. What was even more interesting was that the G-CDs displayed bright green solid-state fluorescence, and exhibited potential application in anti-counterfeiting.