The colorimetric detection of Pb2+ by using sodium thiosulfate and hexadecyl trimethyl ammonium bromide modified gold nanoparticles

A simple, rapid colorimetric detection method for Pb2+ in aqueous solution has been developed by using sodium thiosulfate (Na2S2O3) and hexadecyl trimethyl ammonium bromide (CTAB) modified gold nanoparticles (Au NPs). Na2S2O3 was added into the Au NP solution and thiosulfate ions (S2O32-) were adsorbed on the surface of the Au NPs due to electrostatic interactions. Au atoms on the surface of the Au NPs were then oxidized to Au(I) by the O-2 that existed in the solution in presence of thiosulfate. The addition of Pb2+ (the final concentration was lower than 10 mu M), accelerated the leaching of the Au NPs, and Pb-Au alloys also formed on the surface of the Au NPs. There was an obvious decrease in the surface plasmon resonance (SPR) absorption of the Au NPs. The lowest concentration for Pb2+ that could be detected by the naked eye was 0.1 mu M and using UV-vis spectroscopy was 40 nM. This is lower than the lead toxic level defined by the US Environmental Protection Agency (US EPA), which is 75 nM. In this method, CTAB, as a stabilizing agent for Au NPs, can accelerate the adsorption of S2O32- on the surface of the Au NPs, which shortened the detection time to within 30 min. Moreover, this detection method is simple, cheap and environmentally friendly.