Effect of electric field on localized surface plasmon resonance properties of Fe3O4/Ag composite nanoparticles

The effect of an electric field on the localized surface plasmon resonance named LSPR properties
of Fe3O4/Ag composite nanoparticles was successfully observed. The co-precipitation method was
utilized to synthesize Fe3O4/Ag composite nanoparticles, which were deposited on the surface of
Au thin film-coated BK7 hemispherical prisms. The light source used in this research was a He-Ne
laser beam with a wavelength of 632.8 nm in the Kretschmann array, consisting of a four-layer
material of a prism, Au thin film, Fe3O4/Ag composite nanoparticles, and an air medium. A
prominent resonance improvement in electro-optic activity was observed at the plasmon resonance
frequency. To observe the effect of the applied electric field on the changes in the SPR
properties, electric fields with voltage changes of 0, 2, 4, and 6 volts were applied to a prism/Au
thin film/air layer structure and a prism/Au thin film/Fe3O4/Ag composite NPs/air layer structure.
The SPR angle of the prism/Au thin film/air layer structure was 45.51º. Under an electric
field, the SPR angles shifted by 0.10º, 0.17º, and 0.22º, respectively. In addition, the minimum
reflectance increased from 0.05 to 0.09, 0.13, and 0.15, respectively. The LSPR angle of the
prism/Au thin film/Fe3O4/Ag composite NPs/air layer structure was 46.11º. Under the electric
field, the LSPR angles shifted by 0.03º, 0.06º, and 0.08º, respectively. In addition, the minimum
reflectance also increased from 0.06 to 0.09, 0.11, and 0.13, respectively. The results demonstrate
that the application of an electric field increases the SPR angle and minimum reflectance. As the
electric field increases, the refractive index and the dielectric properties of the environment
surrounding the nanoparticles, causing the LSPR angle and minimum reflectance to increase. The
significant change in the LSPR angle and minimum reflectance due to the application of the
electric field indicates that it is possible to use the EO-LSPR system to optimize the performance of
the SPR biosensor for future applications.