A benzothiazole-based fluorescent probe for distinguishing and bioimaging of Hg²⁺ and Cu²

A new benzothiazole-based fluorescent probe 2-(benzo[d]thiazol-2-yl)-4-(1,3- dithian-2-yl)phenol (BT) with two different reaction sites, a thioacetal group (site 1 for Hg²⁺), and O and N atoms of the benzothiazole dye (site 2 for Cu²⁺), was designed and synthesized. The probe BT showed ratiometric fluorescent response to Hg²⁺ and fluorescence quenching behavior to Cu²⁺, which induces naked-eye fluorescent color changes from green to blue and colorless, respectively. Moreover, it displayed highly sensitivity and selectivity toward Hg²⁺ and Cu²⁺ without interference from other metal ions. The sensing mechanisms were also confirmed by ¹H NMR titration, mass spectrum and Job's plot analyses. Finally, probe BT was successfully used for fluorescent imaging of Hg²⁺ and Cu²⁺ in living cells, demonstrating its potential applications in biological science.