Mercury Speciation with Fluorescent Gold Nanocluster as a Probe

Fluorescent nanoparticles are widely used for sensing biologically significant species. However, there are only rare reports of the discrimination or speciation of metal species. In this work, we report for the first time the speciation of mercury (Hg2+) and methylmercury (CH3Hg+) by taking advantage of the fluorescence feature of folic-acid-capped gold nanoclusters (FA-AuNCs). FA-Au NCs exhibit an average size of 2.08 ± 0.15 nm and a maximum emission at λex/λem = 280/440 nm with a quantum yield of 27.3%. It is interesting that Hg2+ causes a significant quench of the fluorescence of FA-Au NCs, whereas CH3Hg+ leads to a remarkable fluorescence enhancement. On the basis of this discriminative fluorescent response between Hg2+ and CH3Hg+, a novel nanosensor for the speciation of CH3Hg+ and Hg2+ was developed, providing limits of detection (LODs) of 28 nM for Hg2+ and 25 nM for CH3Hg+ within 100–1000 nM. This sensing system is highly selective to mercury. Its practical applications were further demonstrated by the analysis of CH3Hg+ and the speciation of mercury (CH3Hg+ and Hg2+) in environmental water and fish samples.