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The Effect of Ag Concentration of Core-Shell Fe3O4@Ag Nanoparticles for Sensitivity Enhancement of Surface Plasmon Resonance (SPR) - Based Biosensor

The objective of this research is to advance the affectability of Surface Plasmon Resonance (SPR) biosensor utilizing core-shell Fe3O4@Ag nanoparticles (Fe3O4@Ag NPs) with a variation of Ag concentration (20, 40, 60, 80, 100) mM. Fe3O4@Ag NPs were synthesized by the aqueous solution method. The characterization by utilizing X-ray Diﬀractometer (XRD) depicts that the crystal structure of Fe3O4 compares to the cubic inverse spinel structure and based on Transmission Electron Microscopy (TEM) estimation, the particle size average of Fe3O4@Ag NPs is 14.45 nm. The magnetic properties of Fe3O4@Ag NPs were evaluated by Vibrating Sample Magnetometer (VSM), the result appears that the more concentration of Ag increases, the more remanent magnetization (Mr), saturation magnetization (Ms), and coercitivity field (Hc) diminishes. In this research, a Fe3O4@Ag NPs, a spherical nanoparticle consisting of a spherical Fe3O4 core covered by an Ag shell, was used as an active material to enhance the signal detection of SPR, with a wavelength of 632.8 nm in the Kretschmann configuration. The system consists of a four-layer material, i.e., prism/Au film/ Fe3O4@Ag NPs. The results show that the SPR angle shifted to the larger angle of incident light by using Fe3O4@Ag NPs. However, the effect of Ag concentration appears that the more concentration of Ag extends, the lower angle of SPR shifts. The addition of a core-shell in the conventional SPR-based biosensor leads to the enhancement of the SPR biosensor sensitivity if the fractional volume of the core-shell is large.