A benzothiazole-based fluorescent probe for efficient detection and discrimination of Zn²⁺ and Cd²⁺, using cysteine as an auxiliary reagent

This paper describes the design and synthesis of a benzothiazole-based fluorescent probe (H₁) for zinc and cadmium ion detection and discrimination, using cysteine as an auxiliary reagent. Among the various metal ions tested, zinc and cadmium ions induced blue-shifted emissions of probe H₁ from 573 nm to 520 nm and 540 nm, respectively. The addition of cysteine caused the emission of H₁-Cd²⁺ to red-shift back to 573 nm. In contrast, the emission of H₁-Zn²⁺ with the addition of cysteine only decreased without any red-shift of wavelength. Furthermore, confocal laser scanning micrographs of HeLa cells demonstrated satisfactory cell permeability of H₁ and selectivity toward zinc and cadmium ions in living cells. Test strip experiments suggest that probe H₁ can recognise zinc and cadmium ions together by a remarkable fluorescence change, thus providing a convenient method for tracking zinc and cadmium ions in biological systems.