Novel ratiometric fluorescent probe with large Stokes shift for selective sensing and imaging of Zn2+ in live cell

A novel ratiometric fluorescent probe, namely 5-[(3-dicyanoylidene −5.5-dimethyl) cyclohexenyl-1-ethenyl] salicylaldehyde-3′-hydroxybenzohydrazone (DCSH) is presented for the selective sensing of Zn 2+ ion in acetonitrile/water (2/3, pH 7.4) solution. Introducing Zn 2+ ions notably caused the peak emission of DCSH to shift from 560 nm to 646 nm, accompanied with a significant enhancement of its intensity. A vivid change in fluorescence color from yellow to red facilitated the immediate identification of Zn 2+ ions by visual observation. DCSH exhibits substantial Stokes shifts (110 and 196 nm), rapid detection capability (within 10 s) and high sensitivity to Zn 2+ ions, achieving a limit of detection of 31.2 nM. The response mechanism is supposed to involve the block of C = N bond isomerization and excited state intramolecular proton transfer (ESIPT) along with the enhancement of fluorescence through chelation (CHEF) effect. DCSH was effectively utilized for ratiometric fluorescence imaging to monitor exogenous Zn 2+ concentrations in HeLa cells. Significantly, DCSH is capable of monitoring elevated levels of Zn 2+ ion during apoptosis induced by L-Buthionine sulfoximine (BSO).