A facile "off-on" pattern based on one-pot synthesis of N-doped carbon dots for sensitive detection of Ag+ and S2O32-

In this work, a new "off-on" fluorescence strategy for the determination of Ag+ and S2O32- is presented. Nitrogen-doped carbon dots (N-CDs) were synthesized using oxalic acid dihydrate and anhydrous ethylenediamine via a one-pot hydrothermal treatment without further chemical modification. The surface structure and optical properties of the synthesized N-CDs were characterized. The N-CDs emitted bright blue fluorescence with a high quantum yield of 26.01%. Ag+ could selectively quench the fluorescence of N-CDs due to the formation of a N-CDs-Ag+ complex on the surface. The quenching effect demonstrated a linear relationship in the range of 0-14 and 14-80 mu M with a low detection limit (LOD) of 150 nM. Furthermore, S2O32- could combine with Ag+ to generate a more stable Ag+-S2O32- complex, and thus the fluorescence of the N-CDs-Ag+ system could be restored by adding S2O32-. The N-CDs-Ag+ solution behaved as a secondary fluorescent probe to detect S2O32- in the range of 0-50 nM with an extremely low LOD of 1.5 nM. The N-CDs were successfully applied to analyze Ag+ and S2O32- in real samples with satisfactory recoveries (99.04-103.20% and 97.11-99.84%, respectively), implying good applicability in practical analysis.