Abstract
A theoretical analysis and computational study of biomaterial sample detection with surface plasmon resonance (SPR) phenomenon spectroscopy are presented in this work with the objective of achieving more sensitive detection. In this paper, a Fe3O4@Au core-shell, a nanocomposite spherical nanoparticle consisting of a spherical Fe3O4 core covered by an Au shell, was used as an active material for biomaterial sample detection, such as for blood plasma, haemoglobin (Hb) cytoplasm and lecithin, with a wavelength of 632.8 nm. We present the detection amplification technique through an attenuated total reflection (ATR) spectrum in the Kretschmann configuration. The system consists of a four-layer material, i.e., prism/Ag/Fe3O4@Au + biomaterial sample/air. The effective permittivity determination of the core-shell nanoparticle (Fe3O4@Au) and the composite (Fe3O4@Au + biomaterial sample) was done by applying the effective medium theory approximation, and the calculation of the reflectivity was carried out by varying the size of the core-shell, volume fraction and biomaterial sample. In this model, the refractive index (RI) of the BK7 prism is 1.51; the RI of the Ag thin film is 0.13455 + 3.98651i with a thickness of 40 nm; and the RI of the composite is varied depending on the size of the nanoparticle core-shell and the RI of the biomaterial samples. Our results show that by varying the sizes of the core-shell, volume fraction and the RIs of the biomaterial samples, the dip in the reflectivity (ATR) spectrum is shifted to the larger angle of incident light, and the addition of a core-shell in the conventional SPR-based biosensor leads to the enhancement of the SPR biosensor sensitivity. For a core-shell with a radius a = 2.5 nm, the sensitivity increased by 10% for blood plasma detection, 47.72% for Hb cytoplasm detection and by 22.08% for lecithin detection compared to the sensitivity of the conventional SPR-based biosensor without core-shell addition.
Highlights
There is increasing interest in the development of magnetic and plasmonic nanoparticles as active materials for biomolecule detection [1]
We apply the analytical and computational approximation to calculate reflectivity in the attenuated total reflection (ATR) method and determined the effective permittivity of the composite attenuated total reflection (ATR) method and determined the effective permittivity of the composite
If the complex particle is applied to the surface plasmon resonance (SPR)-based biosensor system, this change leads to the enhancement of the sensitivity of this biosensor
Summary
There is increasing interest in the development of magnetic and plasmonic nanoparticles as active materials for biomolecule detection [1]. Biosensors 2018, 8, 75 when the wave vector of the evanescent wave (EW) matches the wave vector of the surface plasmon (SP) under the total internal reflection condition. This resonance condition is expressed as ω0. The variable on left hand side is the propagation constant of a light beam incident at a resonance angle θSPR through the light coupling device (prism) of a refractive index, n p , while the right-hand is the propagation constant with ε m as real part of the metal permittivity and nd as the refractive index of a dielectric material or sensing medium. The evanescent wave occurs at the metal–dielectric interface when a p-polarized wave passes a prism through a metallic layer into a dielectric media
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