Environmental synthesis of yellow fluorescent carbon dots for on-off-on detection of mercury and cysteine

Herein, carbon dots (CDs) with bright yellow fluorescence were synthesized by using kaempferol as a carbon source, through a hydrothermal method in NaOH solution. The as-prepared CDs were highly soluble and spherical with uniform size and mean particle diameter of 3.2 nm. The CDs have unique high selectivity, sensitivity and anti-interference ability to mercury (Hg2+). Under different pH conditions, Hg2+ ions can still quench the fluorescence of CDs effectively and stably. On the other hand, cysteine can re-ignite the fluorescence of CDs as a result of strong chelation interaction that exists between -SH and Hg2+. There are good linear relationships between the concentration of Hg2+ and (F0-F)/F0, the concentration of cysteine and (F-F0)/F0, and the detection limits are 1.6 μM and 0.8 μM, respectively. In addition, CDs can effectively detect Hg2+ in tap water and lake water and detect cysteine in serum.