Ratiometic fluorescent detection of Au(III) and fluorescent “turn-off” identification of Cu(II)/Hg(II) with a coumarin-based probe

A coumarin-based fluorescent probe CHA functionalized with a 2-hydrazone pyridine unit displayed different photophysical responses to Au3+, Cu2+ and Hg2+. It exhibited ratiometric fluorescent response to Au3+, whereas remarkable fluorescence “turn-off” response to Cu2+/Hg2+ in aqueous solution. Au3+ and Cu2+ respectively induced clear blue-shift and red-shift in the absorption maximum, while Hg2+ had little impact on the absorption spectrum. The results of NMR, Job's titration and competition assay reveal that CHA was hydrolyzed to aldehyde under catalysis of Au3+, while it formed complex with Cu2+ and Hg2+. The ratio of fluorescence intensities I490/I540 of CHA exhibited linear relationship to Au3+ concentration in the range of 0.5–5.0 μM with a detection limit of 0.02 μM. The fluorescence intensity at 540 nm was in linearly correlative with Cu2+/Hg2+ concentration. Therefore, CHA could be used for detection of Au3+, Cu2+/Hg2+ in different channels as well as visual differentiation of exogenous Au3+ and Cu2+/Hg2+ in living HeLa cells.