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

Abstract

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 μM 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.