Determination of copper and lead ions using gold nanoparticles as a colorimetric probe with the aid of cysteine

This work describes a simple and reliable colorimetric method based on the gold nanoparticles without any modification, which can realize the rapid, sensitive, and quantitative detection of lead (Pb 2+ ) and copper (Cu 2+ ) ions, providing a reference for monitoring metal ions in the environmental water. When Pb 2+ was added to the gold nanoparticles solution containing a low concentration of L-Cysteine, the combination of Pb 2+ and L-Cysteine can induce the aggregation of gold nanoparticles. On the contrary, Cu 2+ can catalyze the oxidation of L-Cysteine and destroy the formation of the Au-S bond between L-Cysteine and gold nanoparticles, thereby preventing the aggregation of gold nanoparticles. As the ultraviolet-visible spectrum of gold nanoparticle solution is closely related to their aggregation status, the Cu 2+ and Pb 2+ can be determined. The calibration curves, which are constructed based on ratios of the absorbance at 650 nm and 520 nm of gold nanoparticles, display good linearity in the range of 50.0−2.5 × 10 3 nM for Pb 2+ and 25.0−300.0 nM for Cu 2+ , respectively. The limits of quantitation of Pb 2+ and Cu 2+ are determined to be 50.0 and 25.0 nM, respectively. In addition, the spiked recoveries of Pb 2+ and Cu 2+ in real water samples are 94.6−112.5 and 87.3−114.7% with a relative standard deviation of less than 6.3%, respectively.