Colorimetric and fluorescence sensing of Zn2+ ion and its bio-imaging applications based on macrocyclic "tet a" derivative.

We report on the synthesis and characterization of trans N, N'-di-substituted macrocyclic "tet a" probe (L) for metal ion sensing. Both the colorimetric and fluorescent titration studies are performed with different metal ions. The results have suggested that the probe L is very selective and sensitive towards Zn2+ ions with significant changes in color. The pendant armed macrocyclic "tet a" probe has exhibited 1.28× 105 M-1 binding constant and virtuous selectivity for Zn2+ ion than other common metal ions. The detection limit of the probe towards Zn2+ ion is 0.027 nM. The selective sensing of Zn2+ ion is efficiently reversible with EDTA, which is demonstrated for five cycles without losing sensitivity. The time-resolved single-photon counting (TCSPC) studies have determined the average lifetime value for the probe L and L+ Zn2+ ion of 1.29 and 2.96 ns, respectively. The theoretical DFT studies have well supported the experimental outcomes. The practical application of the probe in visualizing intracellular Zn2+ ion distribution in live Artemia salina has proved the low cytotoxicity and cell membrane permeability of probe, which makes it capable of sensing Zn2+ ion in HeLa cells. Thus, the probe L can act as a selective recognition of Zn2+ ion in living cell applications.