A novel dithiourea-appended naphthalimide "on-off" fluorescent probe for detecting Hg2+ and Ag+ and its application in cell imaging.

An effective dithiourea-appended 1,8-naphthalimide fluorescent probe was designed and synthesized. This probe could recognize Hg2+ and Ag+ sensitively and selectively in neutral and alkaline conditions. Moreover, the probe detected Hg2+ alone at pH between 2 and 6. The sensing ability of the probe was explored by UV-vis, fluorescence, FTIR and 1H NMR spectroscopy. The probe was quenched by Hg2+ and Ag+ with 1:1 binding ratios in MeCN/H2O (4/1, v/v) mixed solution with binding constants of 3.76 × 104 L mol-1 and 2.47 × 104 L mol-1, respectively. The linear concentration ranges for Hg2+ and Ag+ were 0-17 μmol L-1 and 0-24 μmol L-1 with detection limits of 0.83 μmol L-1 and 1.20 μmol L-1, respectively, which allowed for the quantitative determination of Hg2+ and Ag+. The new probe, 3a, was successfully applied to the fluorescence imaging of Hg2+ and Ag+ in HepG2 cells, demonstrating its potential application in biological science. Moreover, 3a was used to measure Hg2+ and Ag+ in tap water, drinking water and ultrapure water samples. The recoveries of Hg2+ and Ag+ in water samples were 96-99% and 98-103%, respectively. Therefore, the proposed method showed promising perspectives for its application, aimed at detecting Hg2+ and Ag+ in fluorescence imaging and real water samples.