Effect of Fe₃O₄ Magnetic Nanoparticle Concentration on the Signal of Surface Plasmon Resonance (SPR) Spectroscopy

Effect of Fe₃O₄ magnetic nanoparticle concentration on the signal of surface plasmon resonance (SPR) spectra has been successfully observed. The Fe₃O₄ nanoparticles with a particle size of about 10.5 ± 0.2 nm were used as active materials to increase the SPR response. X-ray diffraction (XRD) pattern showed that Fe₃O₄ nanoparticles have a high degree of crystallinity with spinel structure. The SPR system was successfully set up by using a glass prism coupler in a Kretschmann configuration in which gold (Au) thin film was thermally evaporated on the prism base. A green laser of wavelength 543 nm was used as light source. The angular scan in the attenuated total reflection (ATR) spectra showed a dropping intensity. Those things clearly indicated the appearance of SPR coupling phenomenon on the interface of Au thin film. The SPR spectra of fixed Au masses were also performed with same angular positions of dips. The Fe₃O₄ nanoparticles were deposited on gold thin film as a third layer which was synthesized via co-precipitation method. Hence, it was observed that the variation of Fe₃O₄ concentration affected the SPR spectra profile. The concentrations of Fe₃O₄ nanoparticles are 1, 3, 5, 7, 9, and 11 mg/ml which correspond to the angle shift of 0.1°, 0.3°, 0.5°, 0.7°, 0.9°, and 1.0°, respectively. The SPR angle of the dip was shifted to higher value due to change of refractive index of the medium as Fe₃O₄ nanoparticles concentration increases. Based on this result, we can conclude that the angle shift of SPR increases with increasing concentration of Fe₃O₄ nanoparticles. (paper)