Magnetic–Plasmonic FePt@Ag Core–Shell Nanoparticles and Their Magnetic and SERS Properties

Magnetic-plasmonic FePt@Ag core-shell nanoparticles (NPs) with different Ag shell thicknesses were successfully synthesized using a seed-mediated method. They presented not only localized surface plasmon reso- nance in the visible region, but also superparamagnetic behavior at room temperature. When normalized by the weight of FePt, the saturation magnetization of the FePt@Ag NPs was found to be higher than that of FePt NPs, suggesting that the Ag shell effectively passivated the FePt NP surfaces, avoiding the direct interaction between the FePt core and surface capping ligands that typically forms a magnetically dead layer in FePt NPs. Despite the high colloidal stability and the small size of the FePt@Ag NPs, the NPs were easily separated using a permanent magnet. The surface enhanced Raman scattering (SERS) activity of the FePt@Ag NPs was then examined using thiophenol as a Raman reporter molecule and was found to be equivalent to that of Ag NPs. Moreover, the SERS activity of the FePt@Ag NPs was enhanced when a mag- netic field was applied during the preparation of the SERS substrate (FePt@Ag NP film). These FePt@Ag NPs hold promise as dual-functional sensing probes for environmen- tal and diagnostic applications.