New Selective Fluorescent "Turn-On" Sensor for Detection of Hg2+ Based on a 1,8-Naphthalimide Schiff Base Derivative

A new fluorescent "turn-on" sensor for Hg2+, N-allyl-4-(ethylenediamine-5-methylsalicylidene)-1,8-naphthalimide (HL) has been designed by combining a 1,8-naphthalimide moiety as a fluorophore and a Schiff base as a recognition group. As expected, HL displays high selectivity for Hg2+ over other ions (Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Fe3+, Ni2+, Zn2+, Hg2+, Ag+, Co2+, Cr3+, Mn2+, and Cd2+) with obvious fluorescence enhancement in solution (DMF/Tris-HCl buffer, 1:1, v/v, pH 7.2). Moreover, the fluorescence intensity of HL has shown good linearity with a correlation coefficient (R-2) of 0.99, confirming that HL could be applied to quantitatively detect mercury ions in the range of 0.5-4.0 mu m, whereby the detection limit reaches 0 .26 mu m. Meanwhile, the association constant (K-a) between Hg2+ and HL achieves 7.35 x 10(11) M-1. Based on the fluorescence titration and Job's plot analysis, the formation of a complex between HL and Hg2+ is by 2:1 complex ratio.