Thiourea-based novel fluorescence chemosensor for selective detection of mercuric ion and its application in bio-imaging

Sensitive and reliable fluorescence chemosensors for the monitoring of Hg2+ levels are very important for the protection of environment and living systems. Herein, a simple thiourea-based irreversible fluorescence and colorimetric chemosensor L has been devised and characterised by various spectral analysis. Probe L selectively detects Hg2+ ion due to the binding site-signalling strategy, where the pyridine ring serves as the fluorophore unit and the thiourea moiety serves as the coordinating site. The incorporation of Hg2+ ions to a DMSO solution of L shows substantial alterations in the UV-Vis spectrum and fluorescence spectra. This alteration in absorption as well as fluorescence profile refers to the increase in the intra-molecular charge transfer (ICT) and chelationinduced enhanced fluorescence (CHEF) of L-Hg2+ complex. For the Hg2+ ion, the detection limit is reached up to 2.5 x 10- 8 M, which is calculated from the IUPAC formula CDL = 3 sigma/slope. The Job's plot reveals a 1:1 binding stoichiometry between L and Hg2+. Applying Benesi-Hildebrand equation, the binding constant for the L-Hg2+ complex was estimated as 7.54 x 106 M- 1. To validate the mechanism involved in the formation of L-Hg2+ complex, the DFT and TD-DFT calculations were performed in the gas phase. L has been used well to identify Hg2+ ions in soil samples over a wide pH range. The receptor L was also applied for cell imaging study.