Colorimetric determination of Hg(II) ions based on core/shell Au@MnO2 nanoparticles with oxidase-like activity

In this work, we present core/shell Au@MnO 2 nanoparticles-based visual sensing strategy for mercury ion (Hg 2+ ) detection. The MnO 2 shell of Au@MnO 2 nanoparticles catalyzes the oxidation reaction between tetramethylbenzidine (TMB) and oxygen in the air, generating blue derivative (oxTMB) with an absorption peak at 650 nm. Glutathione (GSH) inhibits the formation of oxTMB, reversing the reaction and turning it back into colorless TMB molecules. While in the existence of Hg 2+ , GSH binds to Hg 2+ due to the strong affinity between the Hg 2+ and the -SH, and in this situation, Au@MnO 2 catalyzes the oxidation of TMB to make the solution become blue. Using the colorimetric sensor, the detection limit of Hg 2+ reached as low as 0.473 nM by UV–vis spectroscopy and 1 nM under the naked eye observation, which is lower than toxicity level of Hg 2+ (10 nM) formulated by the U.S. Environmental Protection Agency.