Synthesis and characterization of fluorescent gold clusters encapsulated in PNIPAM and PAAM hydrogels for selective detection of mercury in water

Abstract

The present work describes the synthesis of new nanomaterials based on gold nanoclusters (AuNCs) supported on poly(N-isopropylacrylamide) (PNIPAM) and polyacrylamide (PAAM) hydrogels, as well as their characterization in terms of structure and physicochemical properties. AuNCs were synthesized by incorporating the metallic precursor (Au³⁺) into the polymeric matrices and subsequently reducing it with UV-vis light (λ = 365 nm). The materials were characterized by UV-vis, FT-IR, fluorescence spectroscopy, TEM and SEM. Likewise, the thermal properties and the swelling capacity of the different polymer matrices were determined. In addition, we present a comparative study with two nanomaterials regarding their behavior for the selective detection of Hg²⁺ in water. Furthermore, it is demonstrated that the polymer matrices influence the nanomaterials' selectivity to mercury. As the AuNCs fluorescence incorporated in both matrices is quenched by Hg²⁺, the materials can be used to sense sensitively and selectively Hg²⁺ in water with a detection limit of 4.1 nM and 1.3 nM for Au-PNIPAM and Au-PAAM NCs, respectively. Summarizing, our study presents a novel, easy and straightforward route to synthesized nanomaterials with unique optical and chemical properties, which could be used for the construction of a portable Hg²⁺ detection device.