Localized surface plasmon resonance properties dependence of green-synthesized Fe3O4/Ag composite nanoparticles on Ag concentration and an electric field for biosensor application

The use of green-synthesized Fe3O4/Ag composites nanoparticles (NPs) on the surface plasmon resonance (SPR) system induced by the electric field generates the effect of electrooptic-localized surface plasmon resonance (EO-LSPR). EO-LSPR is the promising method to increase dispersibility, generate plasmons, bind to biomolecular targets, modify the refractive index, and increase the SPR signal. Green synthesis of Fe3O4/Ag NPs has several advantages, including being environmentally friendly, cost-effective, and sustainable. This research successfully investigated the EO-LSPR properties of green-synthesized Fe3O4/Ag NPs with various Ag concentrations. Green synthesis of Fe3O4/Ag composites NPs was prepared utilizing Moringa oleifera by an aqueous solution method. The EO-LSPR phenomenon was investigated by applying various voltages in the Kretschmann configuration with a layer arrangement of a prism/Au thin film/NPs/air with a wavelength of 632.8 nm. Transmission electron microscope results show that the average size of Fe3O4/Ag particles is around 16.72 ± 7.30 nm. The scanning electron microscopy-energy dispersive x-ray results showed that Ag was distributed on the surface of Fe3O4. The addition of Ag concentration decreased the saturation magnetization while the coercivity field increased. The SPR angle of the prism/Au thin film/air layer structures is 44.66°. After depositing with Fe3O4/Ag with an Ag concentration of 60 millimolar, the LSPR angle shifted by 0.98°. Under an electric field, the LSPR angle shifted to 1.00°, 1.17°, and 1.22° of 2 volts, 4 volts, and 6 volts, respectively. The results show that applying the electric field induces the LSPR angle of Fe3O4/Ag NPs to shift to a larger angle. Applying an electric field causes a change in the material's refractive index. The greater the applied electric field, the more significant the LSPR angle shifts. The significant shifts in the LSPR angle due to the application of an electric field indicate that the EO-LSPR system using green-synthesized Fe3O4/Ag composites NPs could be a promising alternative to increase the performance of SPR biosensors in the future.