A selective fluorescent sensor for Hg2+ based on covalently immobilized naphthalimide derivative

In this work, a selective fluorescent sensor for Hg2+ detection in aqueous solution, which contains a naphthalimide derivative covalently grafted to the glass surface, was developed. To fabricate the sensor, the naphthalimide derivative (compound 1) with a terminal double bond was prepared and photo-copolymerized with 2-hydroxyethyl methacrylate (HEMA) on the glass surface treated with a silanizing agent. Upon binding mercuric ions in 0.05 mol/L Tris/HCl (pH 7.01) at 25 °C, the resulting optical sensor undergoes fluorescence enhancement. Thus, the proposed sensor with visible excitation can behave as a fluorescent sensor for the selective detection of Hg2+. The fluorescence enhancement was induced by a photo-induced electron transfer (PET) inhibition process. In addition, the proposed sensor showed satisfactory selectivity, reproducibility and response time. The sensing membrane possesses a relatively long lifetime of at least 2 months. The chemosensor can be applied to the quantification of Hg2+ with a linear range covering from 6.0 × 10–6 to 2.0 × 10−4 M and a detection limit of 2.0 × 10−6 M. The determination of Hg2+ in river water samples shows satisfactory results.