Bare gold nanoparticles as facile and sensitive colorimetric probe for melamine detection.

In this study, we demonstrate a more sensitive colorimetric assay for the detection of melamine based on the strong attraction between exocyclic amine groups of melamine and surface-bound AuCl(4)(-)/AuCl(2)(-) ions on bare gold nanoparticles prepared by the borohydride reduction method. This method is rather simple without further modification of gold nanoparticles and complicated pretreatment of samples. The detection limit of the method is 2.0 × 10(-7) g L(-1) for melamine in infant formula, which is much lower (about 1000-fold) than that of using citrate-capped GNPs as a colorimetric probe. The proposed scheme could be a good alternative means for on-site and real-time screening of melamine adulterant in infant formula without costly instruments.