An ESIPT-based fluorescent probe for highly selective and ratiometric detection of mercury(II) in solution and in cells

A novel ratiometric fluorescent Hg2+ detecting system was rationally developed based on the typical excited state intramolecular proton transfer (ESIPT) characteristic of the latent fluorophore, 2-(1-(p- tolyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol (Pol) and the Hg2+-mediated cleavage of the vinyl group. The probe responds selectively to Hg2+ over various other metal ions with a larger bathochromic shift (similar to 100 nm). The sensing mechanism was investigated in detail by fluorescence spectroscopy, NMR spectra and mass spectrometry. Taking advantage of the enhancement effect of dichloromethane on the ESIPT efficiency, a facile dichloromethane extraction was introduced in the process of detection of Hg2+, which affords a high sensitivity for the probe with a detection limit of 7.8 x 10(-9) M for Hg2+. By using the new strategy, the novel probe can be used for the detection of Hg2+ in practical water samples with good recovery. Moreover, the probe was successfully applied to the fluorescence image of Hg2+ in living cells. These results indicated that the probe and the proposed method have promising applications for Hg2+ sensing in biological and environmental sciences.