Phenanthroline-benzothiazole conjugate an "On-Off" fluorescent sensor for Hg(II) and its bioimaging applications

Mercury (Hg) is a hazardous metal with the ability to bio-magnify that poses serious threats to both biotic and human health. It is necessary to design a sensor able to detect Hg2+ in biological and environmental systems. A new phenanthroline-benzothiazole (L) was designed, synthesized, and characterized for detecting Hg2+. The sensor L exhibits a high fluorescence (at 414 nm) in DMSO:H2O (7:3, v/v) solution and upon interacting with Hg2+ only exhibit quenching (at 414 nm). The sensing ability of L towards Hg2+ is attributed to the chelation-enhanced-fluorescence quenching (CHEQ) which is supported by a high Stern-Volmer quenching constant (2.9 x 106M-1). The detection limit was as low as 1.93 nM. The binding stoichiometric complexation ratio between L and Hg2+ was found to be 1:1, which is evidenced by Job's plot, NMR, and ESI mass spectral analysis. Based on the aforementioned results, theoretical calculations (DFT and TD-DFT) were performed. The selectivity of Hg2+ in water samples demonstrates that L may be used to detect environmental samples containing Hg2+. In vitro studies on DrG cells indicate that this could be used to explore biological processes involving Hg2+ in live cells.