Ratiometric Zn²⁺ Fluorescent Sensor and New Approach for Sensing Cd²⁺ by Ratiometric Displacement

A fluorescent sensor QB, based on quinoline with DPA as receptor, is designed as a ratiometric sensor for Zn(2+) and CHEF (chelation enhanced fluorescence) sensor for Cd(2+). Moreover, another ratiometric signal output for Cd(2+) can be observed when the bound Zn(2+) in the QB-Zn(2+) complex is displaced by Cd(2+). These results demonstrate that QB can act not only as a ratiometirc sensor for Zn(2+) but also as a dual-mode Cd(2+)-selective sensor via the CHEF mechanism and ratiometric displacement.