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.