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 2.7×10−8 M and 8.1×10−8 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. A new probe DIPQ (2‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)‐4‐phenylquinoline) that selectively sense Zn2+ ions by switching on its florescence is developed. Detection of Zn2+ ions using DIPQ is free from the interference of other metal ions or anions and sample matrices. DIPQ can detect Zn2+ ions with LOD as 2.7×10−8 M. DIPQ is suitable for the detection of Zn2+ ions in the range of pH 5.5–9.0. Also DIPQ can be used to detect Zn2+ ions even in the biological samples.