Visual and fluorescent detection of mercury ions using a dual-emission ratiometric fluorescence nanomixture of carbon dots cooperating with gold nanoclusters

Mercury (II) ions (Hg2+), as one of the most toxic heavy metals, can cause irreversible damage to human health even at very low concentration due to its high toxicity and bioaccumulation. Herein, a facile ratiometric fluorescence nanomixture based on carbon dots‑gold nanoclusters (CDs-Au NCs) was constructed for quantitative detection of Hg2+. Lysine functionalized carbon dots (CDs) were prepared by one-pot hydrothermal method, while gold nanoclusters (Au NCs) were synthesized via using chicken egg white (CEW) as reducer and stabilizer. The novel nanomixture exhibited two strong emission peaks at 450 nm and 665 nm under 390 nm excitation, and showed pink fluorescence under UV light. Interestingly, the fluorescence of the CDs-Au NCs nanomixture was selectively response to Hg2+. The fluorescence of Au NCs at 665 nm was decreased when Hg2+ was presented in the solution, while the fluorescence of CDs at 450 nm stayed constant. The fluorescence color changed from pink to blue obviously with increasing the concentration of Hg2+, which indicated that CDs-Au NCs could be used for visual detection Hg2+ by the naked eye. Under optimal conditions, this ratiometric fluorescent sensor could detect Hg2+ accurately and possess a great sensitivity with a detection limit of 63 nM. In addition, this method was applied to detect Hg2+ in real water samples with great recoveries, suggesting its potential in practical application with simplicity, environmentally friendly and low cost.