Direct detection of melamine in infant formula milk powder solution based on SERS effect of silver film over...

A direct and sensitive method to detect melamine in infant formula milk powder solution based on the SERS effect of silver film over nanospheres (AgFON) was developed. AgFON was prepared by vacuum magnetron sputtering and dip-coating methods. The surface morphology and roughness were characterized by using scanning electron microscope and atomic force microscope. AgFON was used as a substrate to detect the SERS spectra of melamine in infant formula milk powder solution directly without any pretreatments. Semi-quantitative analyses of melamine with various concentrations in milk powder solution were carried out. A good linearity with correlation coefficient of 0.9926 between peak intensity and concentration was obtained from 2 to 25 mg/L. Furthermore, the as-prepared AgFON substrate had good uniformity with relative standard deviation value of 5.56% collected from ten randomly selected positions. The electric field distribution of AgFON was simulated by finite difference time domain solution, which revealed that the huge enhancement of Raman signals was ascribed to the high-density hot spots of the substrate.