A fluorescence "on-off" sensor for the highly selective and sensitive detection of Cu2+ ion

In an attempt to obtain a model of copper(II) ion-selective sensors, a new 1,8-naphthalimide-based fluorescence chemosensor, N-allylamine-4-[(E)-4-(([2-aminoethyl]imino)methyl) benzene-1,3-diol]-1,8-naphthalimide (NABN), was designed and synthesized. The sensor NABN is fully characterized by melting point analysis, fourier transform infrared spectra, Ultraviolet-visible (UV-vis) spectra, fluorescence spectra, H-1 NMR and C-13 NMR spectroscopy, and mass spectrometry. NABN showed an unrivaled sensing behavior and an ardent selectivity toward copper(II) ion over other competitive metal ions tested in solution (N,N-Dimethylformamide (DMF)/Tris-HCl buffer, 1:1, v/v, pH = 7.2). The sensor showed a linear fluorescence quenching toward copper(II) ion in the range 0-50 mu M, with a detection limit of 1.92 x 10(-7) M estimated. Job's method indicated the formation of a 2:1 coordinative mode of the sensor with copper(II) ion with a high threshold of binding constant of 4 x 10(12) M-1. Combining the above results, the quenching response of NABN toward Cu(II) ions could be ascribed to the strong, intrinsic paramagnetic behavior of Cu(II).