New Schiff base probe for the fluorometric turn-on sensing of Cd2+ ions and bio-imaging application

We report herein a new 4-Cyanobiphenyl-based Schiff base probe, BPC for efficient fluorometric detection of highly hazardous Cd2+ ions. BPC can sense Cd2+ through selective turn-on fluorescence responses in CH3CN/H2O (3:2, v/v; Tris-HCl, pH = 7.4) solution. The 1:1 complex formation between BPC and Cd2+ could block both isomerization of CN and excited-state intramolecular proton transfer (ESIPT) process and meanwhile enhance the molecular rigidity, resulting in chelating enhanced fluorescence (CHEF). The detection limit (10.5 nM) is lower than the WHO drinking water standard (26.7 μM), which renders BPC a likely candidate for sensing of Cd2+ ions in neutral aqueous media. The analytical applicability of BPC for Cd2+ has been tested on the test paper strips. In addition, BPC was applied to image Cd2+ in living HeLa cells and zebrafish.