Colorimetric determination of Hg(II) based on a visually detectable signal amplification induced by a Cu-Au-Hg trimetallic amalgam with peroxidase-like activity

We report on a method for highly sensitive and selective colorimetric determination of Hg(II) via a signal amplification strategy. Cu-Au nanoparticles (NPs) are found to exhibit intrinsic peroxidase-like activity and can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine by H₂O₂. This is accompanied by a solution color change from colorless to green (with an absorption peak at 655 nm). The catalytic capability of the Cu-Au NPs (pale green) is strongly enhanced by a Cu-Au-Hg trimetallic amalgam (bluish), and this effect can be applied directly to the determination of Hg(II). The limit of detection as observed with the unaided eye is 10 nM, which is at least one order of magnitude lower than that of the known AuNP-based colorimetric assay. Due to excellent specificity of the amalgamation process, the assay is highly selective for Hg(II) and is not interfered by other metal ions in up to 0.5 μM concentrations. This assay was successfully applied to the determination of Hg(II) in tap water. In view of these advantages, we expect this colorimetric method to become an attractive tool for the quantitation of Hg(II) in biological, environmental, and food samples. (author)