In recent decades the applications of nanotechnology in the biomedical field have attracted a lot of attention. Magnetic and gold nanoparticles (MNPs and GNPs) are now of interest as selective tools for tumour treatment, due to their unique properties and biocompatibility. In this paper, superparamagnetic iron oxide nanoparticles (MNPs) decorated with gold nanoparticles (GNPs) have been prepared by means of an innovative synthesis process using tannic acid as the reducing agent. The as-obtained nanoplatforms were characterized in terms of size, morphology, structure, composition, magnetic response and plasmonic properties. The results revealed that hybrid nanoplatforms (magnetoplasmonic nanoparticles, MPNPs) composed of a magnetic core and an external GNP decoration, acting in synergy, have been developed. Biological tests were also performed on both healthy cells and cancer cells exposed to different nanoparticle concentrations, upon laser irradiation. GNPs grafted onto the surface of MNPs revealed the ability to convert the received light into thermal energy, which was selective in its detrimental effect on cancer cells.