Colorimetric detection of Hg2+ based on target-mediated growth of gold nanoparticles

We have proposed a colorimetric sensing assay exploiting the formation of gold amalgamation, combining with Hg2+ mediated the growth of gold nanoparticles (AuNPs) for rapid detecting Hg2+ ions with highly sensitivity and selectivity. In our developed approach, Hg2+ is reduced to elemental mercury by citrate-capped AuNPs, forming gold amalgamation on the surface of AuNPs. AuNP-Hg2+ interaction modulates the growth of AuNPs which is formed in the HAuCl4/NH2OH reaction. The rate of AuNP growth is highly dependent on the target concentration. AuNPs with low Hg coverage grow into spherical AuNPs with slow growth rate, which generates red-colored solutions. Whereas, AuNPs with high Hg coverage accelerate the growth of spherical AuNPs with a larger particle size, which generates blue colored solutions. At higher concentration, however, the growth rate of AuNPs begins to decrease. As the concentration of Hg2+ increases till the saturation of Hg onto the surface of AuNPs, the growth of the AuNPs is inhibited due to full coverage of Hg on the AuNP surface. On the basis of this principle, Hg2+ can be well determined ranging from 0.5 to 10 nM with a 0.26 nM of the detection limit.