A study was conducted to prepare iron oxide/gold core/ shell nanoparticles or low-polydispersity plasmonic-superparamagnetic nanoparticles. The study synthesized the large-diameter magnetic plasmonic three-layer composite particles. It was observed during the study that the magnetic force applied on a particle depends on the particle magnetic moment. The study used gold, silver, and SiO2 core/Au shell particles for plasmonic sensing. The study also found that the core/shell structure with the noble metal in the shell can improve the surface plasmon resonance and show a larger peak shifts. The uniformity can be used to determine the sharpness of the surface plasmon resonance, while the polydispersity of the core/shell particles can cause spectral broadening and eliminate the ability to fine tune the resonance.