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 gamma-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 alpha-Fe2O3, the interlayer of SiO2 and the outer layer of Au. After calcination under H-2 and then exposure to air, alpha-Fe2O3 was transformed into gamma-Fe2O3, which provides the hybrid particle magnetic tunability. This metal oxide (gamma-Fe2O3) dielectric core, the SiO2 interlayer and the Au shell spindle nanoparticle resemble a grain of Au nanorice (gamma-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 gamma-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 gamma-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 gamma-Fe2O3 core.