ESIPT performance bis-Schiff base for multifunctional detection of Pb²⁺, Mg²⁺ and Al³⁺ ions through “turn-on” response and its biological application

Benzothiazole, hydrazine/ammonia and salicylaldehyde were selected as basic unit for constructing of bis-Schiff base molecules with excited state intramolecular proton transfer (ESIPT) property. Herein, “turn-on” fluorescent performance and highly sensitive multifunctional fluorescence probes were developed to stably and efficiently detect Pb²⁺, Mg²⁺ and Al³⁺ in biological and environmental samples. Among them, BF-SJ could distinguish Pb²⁺ and Mg²⁺ ions under different pH conditions, while BF-SO could separate Pb²⁺ and Al³⁺ by different emission wavelength. More important, target ions could be distinguished by naked eyes with color change of solution under sun light and ultraviolet lamp. The LOD values of BF-SJ and BF-SO for Pb²⁺/Mg²⁺ and Pb²⁺/Al³⁺ were as low as 31.23 μM, 25.95 μM, 59.57 μM and 1.38 μM, respectively. Ideally, they showed low cytotoxicity and were successfully used for imaging of exogenous Pb²⁺/Mg²⁺ and Pb²⁺/Al³⁺ in HeLa cells. Also, BF-SJ exhibited satisfactory performance in detection of Mg²⁺ in seawater and test paper experiment.