Colorimetric determination and recycling of gold(III) ions using label-free plasmonic HMoO nanoparticles.

A low-cost and environment-friendly sensor was developed for visual determination of gold ions (Au) by using label-free hydrogen doped molybdenum oxide (HMoO) nanoparticles as ratio probes. According to the characterization results of transmission electron microscopy, scanning electron microscopy, X-ray powder diffraction, and Fourier transform infrared spectra, Au is easily reduced to red Au nanoparticles (AuNPs) by blue HMoO nanoparticles. The color change of the solution depends on the concentration of Au, which makes it possible to detect Au visually. Under optimal experimental conditions of pH 4.6, HMoO nanoparticles concentration of 0.075 mg·mL, and reaction time of 7 min, the sensor offers a satisfactory determination range from 0.5 to 70 μM and a good determination limit of 0.45 μM for Au. The concentration of Au as low as 10 μM can be directly distinguished through the naked eye. Additionally, the colorimetric probe has also been proved applicable in environmental water samples. More importantly, the resulting AuNPs have good stability and oxidase-like activity, which may be directly used in sensing, catalysis, energy, and other fields.