Stimuli-Responsive Copolymer-Mediated Synthesis of Gold Nanoparticles for Nanozyme-Based Colorimetric Detection of Mercury(II) Ions

Mercury ion (Hg 2+ ) is an extremely hazardous pollutant to humans, soil, and aquatic life. Nanozyme-based sensing approaches are promising for detecting toxic heavy metal ions. However, applying noble metal nanozymes in developing affordable and portable sensors remains largely unexplored. Herein, a gold nanoparticle (AuNP)-based colorimetric sensor was established for the ultra-trace detection of Hg 2+ by capitalizing the inherent peroxidase-mimetic features of AuNPs for oxidizing the colorimetric indicator 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2 ). AuNPs of size less than 10 nm were directly prepared in aqueous media using a stimuli-responsive, poly(ethylene glycol methyl ether methacrylate)- b -poly(dimethylaminoethyl methacrylate (p(PEGEMA)- b -p(DMAEMA)) block copolymer, synthesized through RAFT polymerization. The block copolymers efficiently interacted with Au 3+ ions toward the formation of stable, monodispersed AuNPs without additional reducing agents or stabilizers. Using TMB, H 2 O 2, and the AuNP colorimetric system, the concentration of Hg 2+ in aqueous media was quantitatively and selectively detected over those of other common interfering metal ions. The selective detection of Hg 2+ was promoted by the Au-Hg amalgamation process, which is correlated with intensity of the colorimetric response. Colorimetrically, Hg 2+ was linearly measured between 10 nM and 3.5 μM and achieved a detection limit of 0.4 nM. Subsequently, an on-field naked-eye sensing strategy was also developed by integrating the colorimetric sensor on a paper analytical device with a detection limit of 3.5 nM. The efficient colorimetric sensing platform for selective and trace detection of Hg 2+ is promising for determining mercury contamination in different water and biological samples.