A “turn-on” fluorescent probe based on coumarin imine for highly selective detection of Al3+ and Zn2+ in water samples and bioimaging of zebrafish

Abstract

A Schiff fluorescent probe (E)-2-hydroxy-N-((4-hydroxy-2-oxo-2H-chromen-3-yl)methylene)benzoylhydrazine (LR) was designed and synthesized from 3-formyl-4-hydroxycoumarin. Probe LR was highly sensitive and selective for Zn²⁺/Al³⁺ ions and produced significant fluorescence changes (from no fluorescence to blue and green fluorescence) response in the mixed solvent DMSO/H₂O (v/v = 9:1). The detection limits of probe LR for Al³⁺/Zn²⁺ ions were 1.82 × 10^-8 M and 8.32 × 10^-7 M, respectively. In addition, the binding mode of probe LR with Al³⁺ /Zn²⁺ ions was determined to be 1:1 by the MS method and ¹H NMR titration. The sensing mechanism of probe LR was attributed to the inhibition of free rotation of imine groups by the incorporation of Al³⁺/Zn²⁺, which effectively reduces non-radiative leaps and produces the CHEF effect, thus enhancing the fluorescence. The Probe LR test paper is capable of identifying Al³⁺/Zn²⁺ using natural light or specific wavelengths of UV light (365 nm), a process that does not rely on any costly equipment. In addition, the paper has been successfully used in real water samples to accurately detect trace amounts of aluminum and zinc ions. Importantly, LR has been successfully used to recognize Al³⁺/Zn²⁺ in zebrafish organisms, demonstrating the potential application of LR sensors in biological and environmental fields.