Comparative Studies on the Quick Recognition of Melamine Using Unmodified Gold Nanoparticles and p‐Nitrobenzenesulfonic Grafted Silver Nanoparticles

Both unmodified gold nanoparticles (AuNPs) and p‐nitrobenzenesulfonic (p‐NBS) grafted silver nanoparticles (AgNPs) were prepared by chemical synthesis, respectively. They could be used for visual detection via the interaction with the twelve amide compounds including melamine. These color changes could be seen with the naked eye directly and monitored by ultraviolet visible (UV‐Vis) absorbance spectra. The recognition mechanism for both nanoparticles was comparatively investigated by the addition of glutathione (GSH) in the presence of melamine, respectively. The triple hydrogen bonding recognition and the attractive van der Waals interactions between melamine (0.5 mg/L) and AuNPs were responsible for the color change during its aggregation (red‐to‐purple or blue), whilst the electron donor‐acceptor interaction between melamine (0.2 mg/L) and p‐NBS modified on the surface of AgNPs resulted in the color changes (yellow‐to‐grey or dark green).