Fabrication of Fe3O4@SiO2@Ag magnetic–plasmonic nanospindles as highly efficient SERS active substrates for label-free detection of pesticides

Abstract

Fe₃O₄@SiO₂@Ag magnetic–plasmonic nanospindles with efficient SERS performance and magnetic responsiveness have been successfully fabricated. Uniform and monodispersed Fe₃O₄@SiO₂ nanospindles were prepared by a robust strategy through annealing the obtained β-FeOOH@SiO₂ nanospindles in hydrogen atmospheres at 350 °C; the SiO₂ shell could be regarded as an interlayer to maintain the morphology and offer a solid support for the further growth of Ag nanoparticles. Ag nanoparticles were introduced via in situ reduction of AgNO₃, and the coverage rate of Ag nanoparticles anchored on Fe₃O₄@SiO₂ was adjusted through regulating the AgNO₃ concentration. Fe₃O₄@SiO₂@Ag magnetic–plasmonic nanospindles can serve as highly efficient SERS active substrates with controllable magnetic aggregation due to steady enrichment of mass molecules in close proximity to abundant hot spots. Moreover, these nanospindles are used for label-free detection of thiram, and the detection limit is as low as 1 × 10⁻⁷ M (about 0.024 ppm), which is lower than the maximal residue limit of 7 ppm in fruits prescribed by the U.S. Environmental Protection Agency. Therefore, such magnetic–plasmonic nanospindles in the magnetic aggregation state may be potentially applied in rapid trace detection of residual pesticides or other specific analytes.