An efficient PET-based probe for detection and discrimination of Zn2+ and Cd2+ in near-aqueous media and live-cell imaging

A newly designed and synthesized quinoline-based chemosensor (DDTQ) is reported for the detection of Zn2+ and Cd2+. The ligand is characterized by all possible spectroscopic techniques. From a pool of different metal ions in aqueous medium, Zn2+ and Cd2+ ions are simultaneously detected by the probe, giving an excellent enhancement in the fluorescence intensity at 445 nm. The fluorescence intensity of DDTQ-Cd is higher than that of DDTQ-Zn. Cd2+ and Zn2+ can be distinguished by using Cu2+ as a tool for sequential quenching where, DDTQ-Zn is responsive towards Cu2+ while DDTQ-Cd is not. It is noteworthy that the novel probe has shown a nanomolar level detection limit of 154 and 126 nM for Zn2+ and Cd2+ respectively. The binding modes of the complexes are also verified by HRMS, Job’s analysis, and by single crystal-XRD analysis. Fluorescence lifetime measurements of the complexes show lifetime values of 28 ns and 26 ns for DDTQ-Zn and DDTQ-Cd complexes respectively. Photoinduced electron transfer (PET) and chelation enhanced fluorescence (CHEF) mechanisms are proposed to be responsible for the enhancement of the fluorescence intensity. The fluorescence intensity of DDTQ in presence of Zn2+ or Cd2+ is stable in the physiological pH range and this prompted us to explore the bioimaging applications in live Vero cells to demonstrate its potential for real-life applications.