Compositional Tuning of Light-to-Heat Conversion Efficiency and of Optical Properties of Superparamagnetic Iron Oxide Nanoparticles

Superparamagnetic iron oxide nanoparticles have played a fundamental role in the recent development of nanomedicine as one of the most popular imaging and therapeutic agents. Recently, the ability of iron magnetic nanoparticles for efficient heat generation under infrared optical excitation has even boosted the interest of the scientific community in this family of nanomaterials. The combination of magnetic and optical heating into a single nanostructure makes possible the development of advanced therapy treatments based on synergetic effects between these two heat sources that, in addition, could be combined with high penetration magnetic imaging. Despite its potential, the application of iron oxide nanoparticles in photothermal treatments is limited because the lack of knowledge about the physical mechanisms behind their light-to-heat conversion capacity. In this work, we have systematically investigated the photothermal efficiency of iron oxide nanoparticles with a variable composition achieved by partial replacement of iron by zinc atoms. We have experimentally found that the light-to-heat conversion efficiency gradually increases with the iron content, suggesting a dominant role of iron related transitions in the heating processes. Experimental data included in this work reveal a simple route to tailor the light activated heating processes in iron oxide nanoparticles toward fully controllable treatments.