An Improved Synthesis of Water-Soluble Dual Fluorescence Emission Carbon Dots from Holly Leaves for Accurate Detection of Mercury Ions in Living Cells

BACKGROUND: Carbon dots (CDs) emitting near-infrared fluorescence were recently synthesized from green leaves. However, the Hg(2+) detection of CDs was limited because of the insufficient water solubility, low fluorescence and poor stability. METHODS: Dual fluorescence emission water-soluble CD (Dual-CD) was prepared through a solvothermal method from holly leaves and low toxic PEI(1.8k). PEG was further grafted onto the surface to improve the water solubility and stability. RESULTS: The Dual-CD solution can emit 487 nm and 676 nm fluorescence under single excitation and exhibit high quantum yield of 16.8%. The fluorescence at 678 nm decreased remarkably while the emission at 470 nm was slightly affected by the addition of Hg(2+). The ratiometric Hg(2+) detection had a wide linear range of 0–100 μM and low detection limit of 14.0 nM. In A549 cells, there was a good linear relation between F(487)/F(676) and the concentration of Hg(2+) in the range of 0–60 μM; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg(2+). CONCLUSION: Dual-CD has ratiometric responsiveness to Hg(2+) and can be applied for quantitative Hg(2+) detection in living cells.