A Naked Eye and Turn-On Fluorescence Detection of Zn2+ Ion by Imidazole-Quinoline-Based Fluorophore and Its Application in Live-Cell Imaging

A novel quinoline-imidazole hybrid conjugate chromophore, 2-(4,5-diphenyl-1H-imidazol-2-yl)-4-phenylquinoline (DIPQ), is designed, synthesized, characterized using NMR, ESI-MS and ESI-HRMS analyses and explored for its ability in detecting a range of biologically relevant cations. Among the various metal ions, DIPQ responds selectively to the addition of Zn2+ with a change in color from colorless to pale yellow along with characteristic green fluorescence at 564 nm. Zn2+ induced absorption and fluorescence changes of DIPQ are not affected by other commonly coexistent metal ions and anions. DIPQ-Zn2+ binding interactions are thoroughly studied using NMR and MALDI-MS analyses. DIPQ is capable to detect Zn2+ even at the nano-molar levels with a limit of detection (LOD) and limit of quantification (LOQ) of 2.7x10(-8) M and 8.1x10(-8) M, respectively. Sample matrices have trivial impact on the Zn2+ detection ability of DIPQ. The quantitative results obtained from the DIPQ method are comparable with the ICP-OES method. Moreover, DIPQ has a wide pH range of operation, exhibited good cell permeability and low toxicity for biological applications. Furthermore, DIPQ is suitable to detect Zn2+ ions present in biological tissues.