Quantitative determination of melamine in milk using Ag nanoparticle monolayer film as SERS substrate

A Raman method employing silver nanoparticle (Ag NP) monolayer film as Surface-enhanced Raman Scattering (SERS) substrate was presented to rapidly detect melamine in milk. The Ag NPs with 80 nm diameter were modified by polyvinylpyrrolidone to improve their uniformity and chemical stability. The treatment procedure of liquid milk required only addition of acetic acid and centrifugation, and required time is less than 15 min. The Ag NP monolayer film significantly enhanced Raman signal from melamine and allowed experimentally reproducible determination of the melamine concentration. A good linear relationship (R2=0.994) between the concentration and Raman peak intensity of melamine at 681 cm−1 was obtained for melamine concentrations between 0.10 mg L−1 and 5.00 mg L−1. This implies that this method can detect melamine concentrations below 1.0 mg L−1, the concentration currently considered unsafe.