A new ‘turn-on’ and reversible fluorescent sensor for Al3+ detection and live cell imaging

Abstract

Herein, we report a new benzothiazole-based azomethine receptor L as a reversible fluorescent sensor for the selective detection of Al³⁺ in buffered aqueous methanol (20 mM HEPES, pH = 6.0, 50% (v/v) CH₃OH). The fluorescence enhancement response of L towards Al³⁺ along with a large blue shift (Δλ = ∼157 nm) may be attributed to the formation of the L–Al³⁺ complex, which results in the inhibition of excited state intramolecular proton transfer (ESIPT) and CN isomerisation as well as the chelation enhanced fluorescence (CHEF). The results of Job's plot and mass spectroscopic analysis support the 1 : :1 stoichiometry of the complex between L and Al³⁺ ions. The proposed complex structure was calculated by applying the DFT method. Furthermore, the applicability of the probe has been tested in BEL-7402 human hepatoma carcinoma cells under a fluorescence microscope, where turn-on, intense bluish green fluorescence was observed in the presence of Al³⁺ ions.