A pyrene based Schiff base probe for selective fluorescence turn-on detection of Hg2+ ions with live cell application

A novel pyrene based free thiol containing a Schiff base derivative PT1 was synthesized via a one-pot reaction and utilized as a fluorescence turn-on probe for Hg2+ ion detection along with live cell imaging. PT1 in DMSO/H2O (v/v = 7/3; pH 7.0) showed fluorescence turn-on response to Hg2+ ions, via chelation enhanced fluorescence (CHEF) through excimer PT1-PT1* formation. The 2:1 stoichiometry of the sensor complex PT1 + Hg2+ was calculated from the Job plot based on UV-Vis absorption titrations. In addition, the binding sites of the sensor complex PT1 + Hg2+ were well established from the H-1 NMR titrations and were supported by the ESI-mass analysis and fluorescence reversibility of PT1 + Hg2+ via the consequent addition of Hg2+ ions and EDTA. The detection limit (LOD) and the association constant (K-a) values of the PT1 + Hg2+ complex were calculated by standard deviation and linear fittings and from the Benesi-Hildebrand plot, respectively. Moreover, the quantum yield (Phi), time resolved photoluminescence (TRPL) decay constant (tau) changes, pH effect and density functional theory (DFT) studies were investigated for the PT1 + Hg2+ sensor system. More importantly, confocal fluorescence microscopy imaging in Hela cells showed that PT1 could be used as an effective fluorescent probe for detecting Hg2+ in living cells.