Optical properties of octahedra core-shell structures
Lim, Xin Yi
Date of Issue2016-04-01
School of Materials Science and Engineering
In recent years, the optical properties of metallic nanoparticles have been a subject of great interest due to the possibilities that they offer for a diverse range of technologies, particularly in the field of biomedicine. An excellent example of such an application would be localized surface plasmon resonance (LSPR) biosensing, which makes use of changes in the LSPR extinction peak of metallic nanoparticles to detect biological interactions. The metallic nanoparticles applied have to be coated to enhance their stability, and to enable functionalization. This paper aims to examine the critical thickness of this coating layer, which is the maximum thickness of coating material that the metallic nanoparticle can be coated with before the biosensor becomes insensitive. Simulations for different shapes and sizes of gold and silver nanoparticles, coated with polyethylene glycol and polyvinylpyrrolidone, were carried out to track changes in the LSPR extinction peak as the coating thickness is increased in each scenario. The critical thickness of polymer is then determined when a further increase in coating thickness fails to produce significant changes in the LSPR extinction peak. From the results, it can be observed that the critical thickness of polymer coating varies with the refractive index of the coating material, as well as the shape, size and material of the nanoparticle. Larger nanoparticle sizes, polymer coatings with higher refractive indices, more refractive index sensitive plasmonic materials, and ellipsoids in the longitudinal direction will all result in higher critical thicknesses. In the near future, these results may have significant impacts on the design of LSPR biosensors. Further research can also be carried out to expand the investigation to cover a wider range of materials and morphology. LSPR biosensors can then be better optimized using these results to increase its efficiency.
Final Year Project (FYP)
Nanyang Technological University