Colorimetric determination of copper ions based on the catalytic leaching of silver from the shell of silver-coated gold nanorods

We have developed a method for the colorimetric determination of copper ions (Cu 2+ ) that is based on the use of silver-coated gold nanorods (Au@Ag NRs). Its outstanding selectivity and sensitivity result from the catalytic leaching process that occurs between Cu 2+ , thiosulfate (S 2 O 3 2− ), and the surface of the Au@Ag NRs. The intrinsic color of the Au@Ag NRs changes from bright red to bluish green with decreasing thickness of the silver coating. The addition of Cu 2+ accelerates the leaching of silver from the shell caused in the presence of S 2 O 3 2− . This result in a decrease in the thickness of the silver shell which is accompanied a change in color and absorption spectra of the colloidal solution. The shifts in the absorption maxima are linearly related to the concentrations of Cu 2+ over the 3–1,000 nM concentration range ( R  = 0.996). The method is cost effective and was applied to the determination of Cu 2+ in real water samples.