Fluorescein-immobilized optical hydrogels: Synthesis and its application for detection of Hg2+

Abstract Hydrogels are attracting carriers for immobilization of small molecules due to their excellent properties, such as low optical background, recyclable and high loading ability. Several advantages will be found in designing optical sensors by utilizing hydrogels, such as the convenience for operation, the easiness to separate from media and the difficulties to introduce impurities to detection environment. As a fluorescein-based sensor for Hg2+, the N-(Fluorescein) lactam-N′-methylethylidene (FLA) was synthesized, and the structure confirmation process was finished by 1H NMR, 13C NMR, FT-IR and mass spectrometry. The interaction of FLA with various mental ions demonstrated the high selectivity to Hg2+, which was proved by UV–Vis and fluorescence spectrometry analysis. Meanwhile, the binding mode of FLA Hg2+ was characterized by FT-IR, 1H NMR and UV–Vis spectrophotometry. Then, counting FLA as functional monomer and MBA as crosslinker, different proportions of acrylamide (AAm), 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) were copolymerized with FLA and N,N′-methylenebisacrylamide (MBA) to prepare hydrogel sensors. The hydrogel sensor was characterized by colorimetry and swelling properties. At last, the prepared hydrogels is capable to respond to different colors of Hg2+ in water or DMSO, and it can be reused after the treatment with ethylenediamine (EDA) solution.