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. Keywords: chlorophyll, polyethyleneimine, polyethylene glycol, ratiometric Hg 2+ detection, A549 cells