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

Abstract

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 (∼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 × 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.