A novel multidentate pyridyl ligand: A turn-on fluorescent chemosensor for Hg2+ and its potential application in real sample analysis.

Abstract

A novel pyridyl-based ligand with multiple binding sites was developed as potential turn on fluorescent probe for mercuric ion. In comparison with other transition metal ions, the ligand displayed a significant optical selectivity and sensitivity for Hg2+ in aqueous solution with a remarkable fluorescence enhancement. The obtained spectroscopic response was related to the inhibition of the photo-chemical mechanism known as photo-induced electron transfer (PET) in the ligand and CN isomerization by Hg2+ binding. A good linearity between fluorescence responses and Hg2+ concentration was obtained in the range 3.3×10-9M-1.6×10-8M and a nanomolar level limit of detection (LOD) (1.4×10-9M~0.28ppb) and limit of quantification (LOQ) (4.8×10-9M~0.93ppb) were obtained. Both LOD and LOQ values are very low compared to the reported permissible Hg2+ level in drinking water (2ppb) by US Environmental Protection Agency (EPA). The possible binding mode between ligand and Hg2+ were determined using Job's plot analysis and density functional theory (DFT) calculations and a complex with 1:1 stoichiometric ratio was suggested. The response of the pyridyl ligand upon Hg2+ addition was noted to be fast without any time delay and reversible. The performance of the ligand at nanomolar level of Hg2+ and real sample application of the proposed method was investigated and satisfactory results were obtained.