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

Temperature-driven, highly sensitive and selective TURN-ON fluorometric detection of Zn2+ by benzothiazole-based probes (L-1 and L-2) 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 degrees 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 (L-1 and L-2) 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.