An excimer process induced a turn-on fluorescent probe for detection of ultra-low concentration of mercury ions

The accumulation of mercury pollution in plants can induce severe injury to human beings. It is a great challenge to monitor ultra-low concentrations of mercury in complicated matrixes. In this study, we successfully developed a strategy Hg -triggered naphthalene-based fluorescent probe 1, which formed excimer that subsequently emitted fluorescence for the successful detection of ultra-low concentrations of Hg . The coordination of N and S atoms with Hg facilitated the formation of excimer from the naphthalene-conjugated planes that were in sufficiently close proximity. Suppression of CN bond rotation also induced the chelation-enhanced fluorescence (CHEF) effect, and the cumulative result of these effects was obvious fluorescent enhancement. Compared with probe 2, the other key factor for detection of Hg is that the electrons of the hydroxyl group can easily transfer to a naphthalene moiety, resulting in an augmented π-electron density that enhanced the π-π stacking of the naphthalene-conjugated excimer. After detailed spectral studies and mechanism discussions, it was realized that probe 1 was able to detect ultra-low concentrations of Hg in PBS buffer solution. The detection limit was calculated to be 1.98 nM. On account of the excellent performances, the probe was successfully applied in monitoring Hg in water and pea sprouts with the potential for application as an advanced warning of contamination.