Facile preparation of N, S co-doped carbon dots and their application to a novel off-on fluorescent probe for selective determination of Hg2+

In this work, citric acid (CA) and glutathione (GSH) were selected as the raw materials for preparation carbon dote co-doped with N and S (NS-CDs) via microwave heating method. The obtained NS-CDs displayed stable and strong blue luminescence with a maximum emission (λem) wavelength of 442 nm and a maximum excitation (λex) wavelength of 371 nm, and their fluorescence quantum yield (FLQY) was 10.9%. The fluorescence of NS-CDs was quenched by silver nanoparticles (AgNPs) through a combination of static quenching effect and inner filter effect (IFE), and could be recovered by Hg 2+ even at nanomolar levels ascribing to redox reaction between Hg 2+ and AgNPs. Based upon this phenomenon, a novel off-on fluorescent probe (NS-CDs - AgNPs) for determination trace Hg 2+ in aqueous solution was constructed using the obtained NS-CDs and AgNPs. Under optimal conditions, NS-CDs - AgNPs exhibited a wide linearity range of 10–90 nM ( R 2 = 0.993) for Hg 2+ and a low LOD of 4.2 nM. NS-CDs - AgNPs was successfully utilized for monitoring Hg 2+ in real water samples with the recoveries of 91.4–108.6% (RSD <5.84%), which indicated that the fluorescent probe has enormous application potential to detect trace Hg 2+ in real water samples. • N and S co-doped carbon dots (NS-CDs) with stable and strong blue luminescence (λem = 442 nm, λex = 371 nm) were fabricated by a one-step microwave-assisted method with citric acid (CA) and glutathione (GSH) as raw materials. • A novel off-on fluorescent probe for selective determination of Hg 2+ was prepared using as-prepared NS-CDs and silver nanoparticles (AgNPs) with limit a detection of 4.2 nM. • The off-fluorescence mechanism between NS-CDs and AgNPs was verified as the combined effect of both IFE and static quenching effect, and the on-fluorescence mechanism of NS-CDs -AgNPs was owing to the redox reaction between AgNPs and Hg 2+ .