Iodide-responsive Cu@Au nanoparticle-based colorimetric assay for sensitive mercury (II) detection

•We presented a colorimetric assay to detect Hg2+ using iodide responsive Cu@Au nanoparticles.•Iodide can induce an obvious color change of the Cu@Au NP solution from gray to red.•This method exhibits a wide response range from 0.1 nM to 70 nM, and the LOD is 0.037 nM.•Cu@Au NPs-based colorimetric probe exhibits excellent selectivity for Hg2+.

Mercury ion (Hg2+) has been recognized as one of the most hazardous metal pollutants that can cause deleterious effects on human health and the environment even at low concentrations. Therefore, monitoring of Hg2+ levels in water is very important in terms of waste management, environmental analysis, toxicology, water safety, and water quality. Here, we provide a highly sensitive and selective colorimetric assay to detect Hg2+ in aqueous solution using iodide responsive core-shell Cu@Au nanoparticles (Cu@Au NPs). Iodide can induce an appreciable color change of the Cu@Au NP solution from gray to red by transforming the interconnected, irregularly shaped nanoparticles to the single, separated, and nearly spherical ones. In the presence of Hg2+, the formation of Cu@Au-Hg nanoalloys can protect the Cu@Au NPs from absorbing more iodide in the solution, the solution color turns pale red. When Hg absorbed on the surface of Cu@Au NPs reaches saturation, Hg prevents iodide from reacting with Cu@Au NPs, thus the solution color remains gray. This method exhibits a wide response range from 0.1 nM to 70 nM, and the detection limit (LOD) of 0.037 nM is obtained. Besides, our Cu@Au NPs-based colorimetric sensor exhibits excellent selectivity for Hg2+.