New colorimetric and fluorometric chemosensor for selective Hg2+ sensing in a near-perfect aqueous solution and bio-imaging

We report a new 7-nitrobenzo-2-oxa-1, 3-diazolyl (NBD)-based chemosensor containing a piperazine derivative, NBDP, for detection of mercury ions in almost 100% aqueous medium. The chemosensor shows sensing exclusively toward Hg2+ with a switch-on fluorescence response at 543 nm, which could be attributed to the blocking of PET (photo-induced electron transfer) process upon complexation with mercury ions. The molar ratio of Hg(Ⅱ) to NBDP in the complex is 1:1 based on the Job's plot and HRMS studies. Optimized configurations of NBDP and NBDP-Hg2+ complexes were simulated by means of DFT calculations. The reversible fluorescence response with low detection limit (19.2 nM) in the pH range of 6.0-7.5 renders NBDP a promising candidate for Hg2+ detection in neutral aqueous environments. For the practical application of the chemosensor, test strips were successfully fabricated for rapid detection of Hg2+ ions. Moreover, the utility of NBDP showing the mercury recognition in Human liver cancer cells (SMMC-7721) and zebrafish as well as in live tissues of Arabidopsis thaliana has been demonstrated as monitored by fluorescence imaging.