A Simple Water-Soluble TREN-1,8-Naphthalimide Fluorescent "Turn-On" PET Sensor for Selective and Reversible Detection of Cu(II) Ion and Application in Cellular Imaging.

A new water-soluble 1,8-naphthalimide fluorophore, TREN-Nap, is synthesized in quantitative yield through a one-pot imidation reaction between 1,8-naphthalic anhydride and tris(2-aminoethyl)amine (TREN). TREN-Nap is then employed as a fluorescent "turn-on" chemosensor for detecting Cu(II) ions in water. The fluorescence titration studies revealed remarkable selectivity and reversible binding affinity of TREN-Nap toward Cu(II) ions, with significant enhancement (turn-on) in fluorescence emission intensity and sensitivity at the micromolar level (0.74 µM, 0.24 ppm). Notably, similar titration studies with other commonly interfering metal cations such as Zn(II), Mg(II), Cd(II), Ni(II), Co(II), Ba(II), Al(III), Pb(II), and Ca(II) caused almost negligible changes in the emission intensity, indicating their weak binding with TREN-Nap. Moreover, TREN-Nap displayed impressive sensing capability for Cu(II) ions even in real water samples. TREN-Nap is further employed as a bioimaging agent in breast cancer (MDA-MB-231) and lung epithelial (L929) cells. These results affirm that TREN-Nap is an excellent fluorescent "turn-on" sensor for Cu(II) ion detection in water and biological media.