Dansyl Based "Turn-On" Fluorescent Sensor for Cu²⁺ Ion Detection and the Application to Living Cell Imaging

A new "turn-on" fluorescent chemosensor based on dansyl derivative was prepared for Cu²⁺ ion sensing. Hydroxyl, imine and azomethine groups in Schiff base derived compound 1 were deliberately introduced for facilitating the binding of Cu²⁺ ion. Of screen metal ions, compound 1 showed a high degree of selectivity toward Cu²⁺ ion. Other interfering metal ions did not affect the fluorescence intensity of compound 1, except Hg²⁺ and Fe³⁺ ions exhibited a significant degree of fluorescence quenching. Upon binding of Cu²⁺ ion, compound 1 displayed a chelation enhanced fluorescence (CHEF) resulting in increasing of the fluorescence intensity. The molecular optimized geometry indicated the binding ratio between compound 1 and Cu²⁺ ion at 1:1 with the binding constant of 1.68 × 10^- 7 M^- 1. The optimized condition for sensing ability of compound 1 with a detection limit of 5 × 10^- 7 M was found at the physiological pH 7.2 with the excitation wavelength of 366 nm. Due to no cytotoxicity and good photophysical properties, compound 1 was extended its application for the detection of Cu²⁺ ion in Vero cells. Compound 1 could be potentially used as an intracellular fluorescent chemosensor for tracking Cu²⁺ ion. Graphical Abstract.