Ratiometric fluorescence In3+ sensing via In3+-triggered tautomerization: Its applications to water samples, live cells and zebrafish

A novel ratiometric fluorescence sensor NCS ((E)-N-(furan-2-ylmethyl)-2-(2-hydroxybenzylidene)hydrazine-1-carbothioamide) was synthesized by a combination of furfuryl isothiocyanate bearing hydrazine and salicylaldehyde. Sensor NCS exhibited a ratiometric fluorescent response toward In3+ via thioamide tautomerization with blue-shifted emission from 484 to 444 nm in a near-perfect aqueous solution. NCS displayed a linear ratiometric relationship to micromolar concentrations (0–60 μM) of In3+ and the detection limit was found to be 2.68 μM. Moreover, sensor NCS exhibited an excellent selectivity for sensing In3+ in real samples as well as live cell and zebrafish. The sensing mechanism was demonstrated through UV–visible, fluorescent and 1H NMR titrations, Job's plot, ESI-MS and theoretical calculations. [Display omitted] •A ratiometric fluorescent sensor NCS was developed for detection of In3+ at neutral pH.•NCS exhibited ratiometric fluorescent response toward In3+ via thioamide tautomerization.•NCS could detect In3+ in living organisms such as live cells and zebrafish, for the first time.•Sensing mechanism of In3+ was demonstrated by the spectroscopic studies and calculations.