Visual detection of melamine in raw milk by label-free silver nanoparticles

► The Ag NPs-based visual assay was established to detect melamine in raw milk. ► Mechanism was discussed by TEM, spectral analysis and design of control experiments. ► The detection results of melamine in raw milk can be observed by naked eyes and absorption spectra. ► The assay possesses the merits of rapidness, cheapness and simple pretreatment.