Highly Sensitive Detection of Hg²⁺by a Reaction-Based Dendritic Fluorescent Polymer Chemosensor

Abstract

In this work, spherical polymer-based fluorescent sensor with high sensitivity for Hg 2＋ was first designed and synthesized. Dendritic hyperbranched poly(phenylene sulfide) (HPPS) with an average molecular weight of 10.910 kD and spherical conformation was synthesized via one-pot reaction procedure with 2,4-dichlorothiophenol as monomer. Because of aryl groups conjugated with sulfur atoms and dendritic topology, HPPS displayed remarkable chemical stability, fluorescent and multiple reaction sites. It inspires us to employ it as a smart matrix to develop polymer fluorescent sensor. Through the nucleophilic substitution and hydrolysis reaction, peripheral Cl atoms of HPPS were modified by NH 2 groups, and the resulted HPPS-NH 2 was achieved. The fluorescent sensor (HPPSNT) was fabricated by HPPS-NH 2 azo N＝N covalently bonded to small probe molecule Benzamide, It was found that the decreased absorption of fluorescent signal intensity was proportional to the mercury content concentration in a range of 2.5～100 nmol/L with a coefficient of correlation R of 0.9931, and a detection limit of 0.46 nmol/L. The mechanism of high sensitivity was discussed. HPPS was rich in sulfur atoms inside, which has a strong affinity for Hg 2＋ , Cu 2＋ , Fe 3＋, Ag ＋ , consequently, fluorescence of HPPS-NH 2 was quenched dramatically in the presence of these ions. As the peripheral small probe molecules preferentially reacted with Hg 2＋ via desulfurization and cyclization reaction, it is by such reactions instead of by quenching to cause fluorescence intensity of HPPSNT weakened. The decline of fluorescence intensity via desulfurization and cyclization reaction can be explained through the simulation calculation of bond length by Gaussian 09.