Selective and Sensitive Fluorescein-Benzothiazole Based Fluorescent Sensor for Zn²⁺ Ion in Aqueous Media

An efficient fluorescent sensor based on fluorescein-benzothiazole (FB) for Zn²⁺ ion was synthesized and characterized systematically. FB exhibited selective and sensitive recognition toward Zn²⁺ in MeCN-H₂O (v/v = 2/1) over other cations due to the spirolactam ring-opening power of Zn²⁺. The complexation property of FB with Zn²⁺ ion was examined by ¹H NMR, ¹³C NMR and FTIR experiments. The stoichiometric ratio of the FB-Zn²⁺ complex was determined from a Job plot to be 1:1. The binding constant (K _a) of Zn²⁺ binding to FB was found to be 4.22 × 10⁴ M^- 1, with a detection limit of 5.64 μM. In addition, the practical utility of FB was explored in the form of test strips. Graphical Abstract.