Sandwich-structured Fe₂O₃@SiO₂@Au nanoparticles with magnetoplasmonic responses

We report a method for the fabrication of relatively uniform sandwich-like core-interlayer-shell nanostructures by using γ-Fe₂O₃ as the inner core, SiO₂ as the interlayer, and relatively uniform gold (Au) as the outer shell. The resulting novel hybrid nanoparticle combines the intense local fields of nanorods with the highly tunable plasmon resonances of nanoshells. The length and diameter of the resulting nanoparticles can be tuned by the aspect ratio of α-Fe₂O₃, the interlayer of SiO₂ and the outer layer of Au. After calcination under H₂ and then exposure to air, α-Fe₂O₃ was transformed into γ-Fe₂O₃, which provides the hybrid particle magnetic tunability. This metal oxide (γ-Fe₂O₃) dielectric core, the SiO₂ interlayer and the Au shell spindle nanoparticle resemble a grain of Au nanorice (γ-Fe₂O₃@SiO₂@Au ellipsoids). The core-interlayer-shell geometry possesses greater structural and magnetic tunability than a nanorod or a nanoshell. The plasmon resonance of this novel γ-Fe₂O₃@SiO₂@Au geometry is believed to arise from a hybridization of the primitive plasmons of an ellipsoidal cavity inside a continuous Au shell. The unique magnetoplasmonic properties of this γ-Fe₂O₃@SiO₂@Au nanostructure are highly attractive for applications such as surface plasmon resonance sensing because of the dipole resonance of the resultant nanostructure and recyclable catalysts arising from the outer Au layer and the inner magnetic γ-Fe₂O₃ core.