A reversible, benzothiazole-based “Turn-on” fluorescence sensor for selective detection of Zn2+ ions in vitro

Abstract

Temperature-driven, highly sensitive and selective “TURN-ON” fluorometric detection of Zn2+ by benzothiazole-based probes (L1 and L2) was reported in physiological pH in the present work. Iron(II) acted as the reversible switch or trigger for the reversible detection of Zn2+ ions by the probes resulting in “TURN-OFF” fluorescence at room temperature. However, selective detection of Zn2+ in the presence of Fe2+ was irreversible at 0–5 °C. Such temperature dependence on reversible fluorometric detection of Zn2+ in the presence of Fe2+ was explained from the thermodynamic perspective as well as DFT calculations in which the absolute enthalpy (H) and Gibbs free energy (G) of the resultant complexes and the fluorophores (L1 and L2) at different temperatures were determined. Enhanced fluorescence of the Zn2+ bound probes was due to the inhibition of excited-state intramolecular proton transfer (ESIPT). Effect of solvents, pH, and temperature on the fluorometric detection of Zn2+ was also probed in the present work. The results were translated into the visual detection of Zn2+ on paper-based fluorescence probe and later we demonstrated the sensing of mobile Zn2+ ions by the probes in living HeLa cells as the proof of concept of our present investigations. A benzothiazole-based, “TURN-ON” fluorescent sensor was developed for selective and reversible detection of Zn2+in vitro, in which Fe2+ acted as the reversible switch.