A one-step colorimetric method of analysis detection of Hg2+ based on an in situ formation of Au@HgS core-shell structures.

A new approach for the detection of Hg(2+) is reported based on color changes from which gold nanoparticles (Au NPs) are surrounded by a layer of HgS quantum dots to form in situ Au@HgS core-shell nanostructures. The surface plasmon resonance (SPR) absorption of the gold core was changed due to a shell layer of HgS formed on the surface of the Au NPs, which brings the colour change of the aqueous solution. Therefore, Hg(2+) can be recognized by visualizing the colour change of the Au@HgS core-shell nanostructures, and can be detected quantitatively by measurement of the UV-vis spectra. Some effects on the detection of Hg(2+) were investigated in detail. This method was used to detect Hg(2+) with excellent selectivity and high sensitivity. In our method, the lowest detected concentrations for mercury ions were 5.0 × 10(-6) M observed by the naked eye and 0.486 nM as measured by UV-vis spectra. At the range from 8.0 × 10(-5) to 1.0 × 10(-8) M of Hg(2+), this method was shown to have a good linear relationship.

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

A simple, rapid colorimetric detection method for Pb(2+) 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 (S2O3(2-)) 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 O2 that existed in the solution in presence of thiosulfate. The addition of Pb(2+) (the final concentration was lower than 10 µM), 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 Pb(2+) that could be detected by the naked eye was 0.1 µM 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 S2O3(2-) 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.

A rapid colorimetric detection method of trace Cr (VI) based on the redox etching of Ag(core)-Au(shell) nanoparticles at room temperature.

A rapid colorimetric detection method of trace Cr (VI) in aqueous solutions has been developed based on non-aggregated Ag(core)-Au(shell) nanoparticles. It is based on the fact that Cr (VI) redox etches Ag(core)-Au(shell) nanoparticles at the present of bromide ions of hexadecyl trimethyl ammonium bromide (CTAB). The etching process of Ag(core)-Au(shell) nanoparticles would lead to a blue shift in the surface plasmon resonance (SPR) absorption peak as the size of Ag(core)-Au(shell) nanoparticles decreased. This colorimetric strategy based on size and component dependence of core-shell nanoparticles during the etching process provided a highly sensitive and selective detection method toward Cr (VI). Compared with other detection methods, this method provided a wide linear detection range from 1×10(-8) M to 8×10(-6) M over one order of magnitude, also has some practical capability. The cost-effective probe in this colorimetric method allowed rapid and sensitive detection of trace Cr (VI) ions as low as 1.0×10(-7) M based on the observations by the naked eyes and 1.0×10(-8) M based on the measurements of UV-vis spectra in aqueous solutions at room temperature. According to the preliminary data, it indicated that the current method showed very promising practical applicability for the determination of Cr (VI) in real environmental samples.