A facile approach has been developed to synthesize multifunctional magnetic Fe₂O₃/Au/Ag hybrid nanoparticles. UV-vis and SEM were employed to characterize the optical properties and surface structures. By changing the amount of AgNO₃, Fe₂O₃/Au/Ag hybrid nanoparticles with different Ag shell thicknesses and surface structures have been prepared. SERS activities of as-prepared nanoparticles with different Ag shell thicknesses were investigated by using thiophenol (TP) as probe. The results revealed that SERS activities were dependent on the changes in the surface structures. The maximum SERS effect was observed on the Fe₂O₃/Au/Ag hybrid nanoparticles which exhibited the optical absorbance of Ag and Au simultaneously. It might be associated with the pinhole effect and the coupling effect between Ag and Au. Moreover, the efficiency of the magnetic enrichment has been investigated by in-situ monitoring the changes in the SERS signal of the TP with low concentration. The results indicated that the limitation of SERS detection was increased by magnetic enrichment and the magnetic enrichment capacity of Fe₂O₃/Au/Ag was weaker than that of Fe₂O₃/Au, while the SERS signal of the former was stronger than the latter.

Key words: magnetism, core/shell nanoparticle, enrichment, surface enhanced Raman spectroscopy (SERS)