In situ microwave-assisted preparation of NS-codoped carbon dots stabilized silver nanoparticles as an off-on fluorescent probe for trace Hg2+ detection

An off-on fluorescent probe (NS-CDs-AgNPs) was synthesized based on a one-pot microwave process by utilizing N, S co-doping carbon dots (NS-CDs) and silver nitrate as precursors. The significant peak of NS-CDs-AgNPs at 393 nm in ultraviolet spectrum indicated silver nanoparticle (AgNPs) were successfully synthesized. A faint blue fluorescence emission (442 nm) was displayed when excited NS-CDs-AgNPs at 371 nm. A remarkable fluorescence recovery was observed upon adding of trance Hg2+, whereas the other heavy metal ions did not elicit this response. The reason for this phenomenon was revealed in this work that a spontaneous redox reaction occurred between NS-CDs-AgNPs and Hg2+, which leaded to the formation of NS-CDs-Agn-2NPsHg complexes. On the basis of this mechanism, a new off-on fluorescent analytical method was constructed for Hg2+ detection with linear range of 10–400 nM (R2 = 0.9941), and the detection limit (LOD) of 5.16 nM. Additionally, satisfactory recovery (90.28%–106.13%) and the relative standard deviation (RSD) (RSD＜5.21%) were obtained in water sample detection. More importantly, the NS-CDs-AgNPs exhibited lower cytotoxicity and better biocompatibility, indicating a huge potential in cell imaging and clinical medicine.