Iron oxide nanospheres: dual functionality as MRI contrast agents and magnetic fluid hyperthermia therapeutics

Magnetic nanoparticles offer the possibility of combining diagnostic and therapeutic purposes within a single nano-object. In this work, we explore two distinct sets of iron oxide-based nanospheres for their application as contrast agents in magnetic resonance imaging and as heating mediators in magnetic fluid hyperthermia. The nanoparticles were produced with the <i>green</i> microwave polyol-assisted method. The nanoparticles in the first set have a mean core diameter of 11 nm and are coated with polyacrylic acid (PAA), carboxymethyl-dextran (CM-D), or dimercaptosuccinic acid (DMSA). The second set has nanoparticles of a mean diameter of 14 nm, which are coated with PAA or CM-D. The longitudinal and transverse ¹H-NMR nuclear relaxivities (<i>r</i>_1,2) exhibit a field behavior that depends on the particle core size and on the coating. It is shown that the combination of size and coating is relevant to optimize the relaxometric efficiency, with the PAA coating being able to double the <i>r</i>₂ efficiency for the smallest size. The heating release was evaluated under various combinations of external alternating magnetic fields, with frequency values ranging from 102.2 kHz to 971.2 kHz and amplitude values ranging from 7 mT to 40 mT. The results indicate that the heating efficiency is independent of the coating for both the 11 and 14 nm particles, while it is significantly higher for the samples of largest size. We conclude that the combination of size and coating (<i>i.e.</i>, surface modifications) of the magnetic nanoparticles can play a crucial role in the relaxometric and heating properties of magnetic nanoparticles with core size of <15 nm.