Single-step synthesis of highly photoluminescent carbon dots for rapid detection of Hg with excellent sensitivity.

Carbon dots (C-dots) are superior in the aspects of excellent water solubility, good biocompatibility, environmentally friendliness and non-blinking fluorescence. In this work, highly photoluminescent small-size C-dots (QY = 18.8%, quinine sulfate as standard) with narrow size distribution (1.70 ± 0.21 nm) have been synthesized by using citric acid and triethylamine through hydrothermal method. The optimal excitation and emission wavelength of C-dots are 350 nm and 437 nm, respectively. And the prepared C-dots display excitation-independent behavior due to less surface defects and uniform size. Interestingly, the fluorescence of C-dots could be rapidly and selectively quenched by Hg within 200 s at room temperature without further modification. Under optimal conditions, the limit of detection (LOD) was measured to be nanomolar level (2.8 nM) with a linear range of 0.05-7 μM, lower than the previous published reports. Furthermore, our results reveal that static quenching mechanism was dominated in the process in which Hg coordinate with the oxygen-containing groups of C-dots to form nonfluorescent complexes. And only the addition of Hg destroyed the surface defects of C-dots resulting in the fluorescent quenching. The presence of other common interfering metal ions reported in previous literature (Ag, Cu, Fe) do not affect the surface defects, which has rarely been reported before. Besides, this sensing platform has been further successfully applied to the label free detection of Hg in tap water and living cells. These conclusions demonstrate the great potential of our C-dots in selective detection of environmental and cellular Hg, which may achieve a lot of achievements in clinical diagnosis and other biological researches.