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 Hg2+ 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 PEI1.8k. 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 Hg2+. The ratiometric Hg2+ detection had a wide linear range of 0-100 mu M 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 Hg2+ in the range of 0-60 mu M; the detection limit was 477 nM. Furthermore, Dual-CD showed visual fluorescence change under Hg2+. Conclusion: Dual-CD has ratiometric responsiveness to Hg2+ and can be applied for quantitative Hg2+ detection in living cells.

Automated summary

The study synthesized Dual-CD with dual fluorescence emission water-soluble CD from holly leaves and low toxic PEI1.8k through a solvothermal method. It showed ratiometric responsiveness to Hg2+ with excellent detection performance. Application in A549 cells demonstrated that Dual-CD could be used for quantitative detection of Hg2+ in living cells.