Graphitic Carbon Nitride Quantum Dots in Dual-Mode Fluorescence Switching Platforms for Trace Analysis of Ag(I) and l-Cysteine

Graphitic carbon nitride quantum dots (g-C3N4 QDs) are synthesized using a simple, one-pot, and methylamine-assisted hydrothermal method. This material with excellent fluorescence property can be contracted in dual-mode fluorescence switching platforms for trace analysis of Ag(I) and cysteine. Upon adding Ag(I), the fluorescence intensity of g-C3N4 QDs is quenched quickly, but its fluorescence resonance light scattering (RLS) intensity increases owing to the synergistic mechanism between photo-induced electron transfer and chelation mechanisms. Upon subsequently adding cysteine, the fluorescence intensity of g-C3N4 QDs recovers rapidly; however, its RLS intensity decreases obviously due to the strong binding ability between Ag(I) and thiols. According to this interesting reaction mechanism, an “on–off–on” and “off–on–off” dual-mode fluorescence switching sensor exhibits high selectivity and sensitivity for simultaneously analyzing Ag(I) and cysteine, and the detection limits are calculated to be 8.0 and 10.3 nmol L–1, respectively. The present study also displays excellent analytical performance for the analysis of Ag(I) and cysteine in natural samples.