Eco-friendly colorimetric detection of mercury(II) ions using label-free anisotropic nanogolds in ascorbic acid solution

We report a simple, direct, and eco-friendly method of detecting mercury ions in water samples based on the color change of hexadecyltrimethylammonium bromide (CTAB)-coated nanogold (NG) in the presence of nontoxic ascorbic acid (AA). The surface plasmon resonance (SPR) absorption wavelength of the NG shifted from long (dark purple) to short (red) wavelengths results from the amalgamation process between Hg and Au. The detection scheme based on SPR property of NGs with a mixture of spherical and rod-shaped gold nanoparticles offers excellent selectivity and good sensitivity. The lowest detected concentrations for mercury ions were 1 μM by the naked eye and 30 nM by UV-visible light spectroscopy. The total procedure takes less than 5 min without sample pre-treatment. It is successfully applied in mercury ion analysis in tap water and this provides a good potential for on-the-spot detection of mercury ions with simplicity, rapidity, cost-effectiveness, and harmlessness.