A novel "off-on" ratiometric fluorescent probe based on nitrogen-doped carbon dots for silver ion and glutathione...

Dual-emissive nitrogen-doped carbon dots (N-CDs) with yellow fluorescence was prepared by one-step solvothermal method with o-phenylenediamine (OPD) and quercetin (QR) as precursors, and its preparation conditions (like effects of different dosage ratios of QR and OPD, time and temperature) were investigated in detail. Meanwhile, the N-CDs showed two emission peaks at 465 and 568 nm under the excitation wavelength of 395 nm and its quantum yield was 11.3 % using rhodamine 6G as a reference standard. Then the N-CDs as a novel ratiometric fluorescence probe (RF-probe) was employed to selectively sense Ag⁺ according to its fluorescence quenching, which exhibited a much wider linear range (0.05-80.0 μM) and lower limit of detection (LOD, 17.8 nM) than the Y-CDs (yellow carbon dots) and BY-CDs (physically mixing the B-CDs (blue carbon dots) and Y-CDs) did. Interestingly, glutathione (GSH) could recover the fluorescence of the N-CDs@Ag⁺ system. Based on this, an off-on switching system was constructed to monitor GSH with the linear range of 0.015-0.48 μM and low LOD of 5.5 nM. Furthermore, the effect of silver ion doses on the RF-probe construction and the sensing mechanisms of the N-CDs@Ag⁺ and N-CDs@Ag⁺-GSH systems were also further discussed. Meanwhile, the high recoveries in water and fruit samples (94.6 %-107.9 % and 91.3 %-108.7 %) were observed, which proved that the N-CDs and N-CDs@Ag⁺ probes were reliable for the Ag⁺ and GSH assays, respectively.