Ag-Coated Fe₃O₄@SiO₂ Three-Ply Composite Microspheres: Synthesis, Characterization, and Application in Detecting Melamine with Their Surface-Enhanced Raman Scattering

Ag nanoparticles with average sizes of 20 nm were well-dispersed on the surfaces of Fe 3 O 4 @SiO 2 composite microspheres through a simple wet-chemical method employing the Ag-mirror reaction. The as-synthesized Ag-coated Fe 3 O 4 @SiO 2 three-ply composite microspheres are monodisperse and bifunctional, with ferromagnetic and surface-enhanced Raman scattering (SERS) properties. The products were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray analysis (EDX). SERS signals of typical analytes such as rhodamine 6G (Rh 6G) were observed on Ag nanoparticles from the Ag-coated Fe 3 O 4 @SiO 2 microspheres, even though the concentration of the analyte was as low as 1 × 10 −15 M (Rh 6G). The Ag-coated Fe 3 O 4 @SiO 2 microspheres were applied to detecting melamine, and strong SERS signals were obtained with melamine concentration of 1 × 10 −6 M. This work may provide a potential and unique technique to detect melamine.