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-C 3 N 4 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-C 3 N 4 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-C 3 N 4 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.