Colorimetric sensing of silver(I) and mercury(II) ions based on an assembly of Tween 20-stabilized gold nanoparticles.

We have developed a rapid and homogeneous method for the highly selective detection of Hg(2+) and Ag(+) using Tween 20-modified gold nanoparticles (AuNPs). Citrate ions were found to still be adsorbed on the Au surface when citrate-capped AuNPs were modified with Tween 20, which stabilizes the citrate-capped AuNPs against conditions of high ionic strength. When citrate ions had reduced Hg(2+) and Ag(+) to form Hg-Au alloys and Ag on the surface of the AuNPs, Tween 20 was removed from the NP surface. As a result, the AuNPs were unstable under a high-ionic-strength solution, resulting in NP aggregation. The formation of Hg-Au alloys or Ag on the surface of the AuNPs was demonstrated by means of inductively coupled plasma mass spectroscopy and energy-dispersive X-ray spectroscopy. Tween 20-AuNPs could selectively detect Hg(2+) and Ag(+) at concentrations as low as 0.1 and 0.1 microM in the presence of NaCl and EDTA, respectively. Moreover, the probe enables the analysis of AgNPs with a minimum detectable concentration that corresponds to 1 pM. This probe was successfully applied to detect Hg(2+) in drinking water and seawater, Ag(+) in drinking water, and AgNPs in drinking water.