A facile, cost-effective and sensitive colorimetric detection method for Pb(2+) has been developed by using glutathione functionalized gold nanoparticles (GSH-GNPs). The sensitivity and selectivity of detection were investigated in detail. The GSH-GNPs could be induced to aggregate immediately in the presence of Pb(2+), especially after the addition of 1 M NaCl aqueous solution. The Pb(2+) could be detected by colorimetric response of GNPs that could be monitored by a UV-vis spectrophotometer or even naked eyes, and the detection limit could reach 100 nM. The GSH-GNPs bound by Pb(2+) showed excellent selectivity compared to other metal ions (Hg(2+), Mg(2+), Zn(2+), Ni(2+), Cu(2+), Co(2+), Ca(2+), Mn(2+), Fe(2+), Cd(2+), Ba(2+), and Cr(3+)), which led to prominent color change. This provided a simple and effective colorimetric sensor (no enzyme or DNA) for on-site and real-time detection of Pb(2+). Most importantly, this probe was also applied to determine the Pb(2+) in the lake samples with low interference and high sensitivity.

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A simple, cost-effective yet rapid and sensitive colorimetric sensor for the detection of Hg(2+) using L-cysteine functionalized gold nanoparticles induced by ultraviolet radiation was developed. The sensitivity and selectivity of detection was also investigated. The L-cysteine modified gold nanoparticles can be induced to aggregate quickly in the presence of Hg(2+), especially with the assistance of ultraviolet radiation. The presence of Hg(2+) can be monitored by the colorimetric response of gold nanoparticles. The detection of Hg(2+) could be realized, after measuring the UV-vis spectra, with a detection limit of 100 nM. The selectivity of this method has been investigated by other divalent metal ions. The effective colorimetric sensor can be used for on-site and real-time Hg(2+) detection.