Thick-Shelled Magnetite-Gold Core–Shell Nanoparticles: Oleic Acid-Mediated Overcoating for Extended Optical Tunability

A novel synthesis of gold-coated magnetite nanoparticles (Fe3O4@Au NPs) with a thick shell has been developed using well-established wet chemistry methods, specifically chemical coprecipitation. Comprehensive characterization of these nanoparticles was conducted using SEM, EDS, and TEM to examine their structural and surface morphology, as well as their chemical composition. FTIR measurements were employed to investigate the adsorption mechanism of gold onto the magnetite surface. Lastly, the optical properties of the Fe3O4@Au NPs were characterized using UV–vis spectroscopy and further analyzed through computational modeling via the Finite Element Method (FEM). These computational results were validated against analytical solutions from Mie theory to explore the plasmonic properties of the nanoparticles with varying core sizes and shell thicknesses. The findings show a significant enhancement in spectral tunability, showing that the optical spectrum of the composite particles can be precisely tailored over a much wider range than is possible with solid gold nanoparticles. This tunability has a dependence on geometric parameters, such as shell thickness and core size.