Theoretical investigation of optical properties of optimal architectures of magnetoplasmonic nanoparticles in human tissue for potential applications in photothermal therapy

Abstract The absorption and scattering efficiencies of light by a single magnetoplasmonic nanoparticle, based on magnetite and gold, embedded in human tissue are analyzed theoretically in the framework of Finite-Difference-Time-Domain method and Lorenz-Mie theory. We consider separately three different architectures for the magnetoplasmonic nanoparticle: rectangular three-layer gold/magnetite/gold nanobar, circular three-layer gold/magnetite/gold nanoring and magnetite/gold core/shell nanosphere. We address the influence of particle sizes and magnetite-layer and gold-layer thicknesses on the optical response of such nanostructures. Particular attention is paid to the effectiveness of these designed nanostructures in photothermal therapy. Our simulation shows that these hybrid nanostructures support the famous localized surface plasmon resonance mode of gold, which manifests itself in the absorption spectrum by an intense peak whose spectral position can be adjusted to be in the first and second NIR-biological windows. The magnitude of the resonant absorption peak as well as that of the corresponding scattering peak vary from one nanostructure to another and, for the same nanostructure, change with its characteristic sizes. The three-layer nanobars as well as the three-layer nanorings can support significant absorption accompanied by significant scattering of light into both NIR-biological windows. For core/shell nanospheres, the low scattering efficiency of light within the second NIR-biological window, together with their large sizes, limit the usefulness of these nanostructures in photothermal therapy operating in the first NIR-biological window only.