Hg2+-activated oxidase-like activity of Ag2S@graphene oxide nanozyme and its naked-eye monitoring Hg2+ application with obvious hyperchromic effect

To improve the selectivity and sensitivity for naked-eye detection of toxic Hg 2+ , water-soluble Ag 2 S nanoparticle stabilized by graphene oxide (Ag 2 S@GO) was identified by virtue of the high catalytic activity of nano Ag 2 S and the excellent physicochemical property of graphene oxide. After its structure and spectral performance were characterized and investigated, it was noted that the proposed Ag 2 S@GO possesses outstanding Hg 2+ -activated oxidase-like activity to oxidize the chromogenic substrate of 3,3′,5,5′,-tramethylbenzidine (TMB) with an obvious hyperchromic effect from colorless to blue in the presence of Hg 2+ exclusively. Under the optimized conditions, the Ag 2 S@GO+TMB system was successfully applied for naked-eye detection of heavy metal Hg 2+ in real environmental samples, with a nmol·L −1 -level detection limit of 9.8 × 10 –9 mol/L, an accurate recovery among 97.0–101.8% and a low standard deviation less than 3.3%. The Hg 2+ -activated oxidase-like activity of Ag 2 S@GO and its exclusive recognition mechanism to toxic Hg 2+ were also proposed.