The effect of chemico-physical parameters of magnetic nanoparticles on their fundamental and biomedical applicative properties: a few case studies

In the last two decades, much attention was devoted to novel multifunctional nanostructures based on magnetic nanoparticles (MNPs) useful as agents for Magnetic Resonance Imaging, Optical Imaging and Magnetic Fluid Hyperthermia, carriers for drugs and vectors for molecular targeting. Most of the MNPs systems reported in literature by a lot of research groups, have been shown to be useful as MRI contrast agents and magnetic fluid hyperthermia (MFH) mediators, displaying high nuclear relaxivity and Specific Absorption Rate (SAR). For these compounds, the possibility to collect images of the regions where the MNPs are delivered through MRI and eventually Optical Imaging (if functionalized with a luminescent molecule), is joint to their use under radio-frequency fields, with frequency of the order of 100 KHz, which causes a local release of heat directed to tumour cells (the MFH effect), possibly inducing their death. By such materials, theranostic agents can be obtained. On the other hand, in the field of drug delivery and molecular targeting, few examples of reproducible experiments using superparamagnetic nanoparticles are actually present in literature. Thus, the applications of MNPs to nanomedicine is currently of growing interest in the world. The main objectives of my research group in the last decade was to contribute to the knowledge of physical mechanisms at the basis of MNPs used in biomedicine (especially MRI) and to propose some novel systems in strict collaboration with different research groups of chemists and biologists. I will present different case studies [1-3] where I show how the chemico-physical characteristics of MNPs are strictly correlated to their properties. Furthermore, I will discuss the failure of the most famous heuristic model [4] used in literature to interpret the NMR relaxivity profiles that does not reproduce transverse relaxivity experimental data and I will try to present which possible mechanisms are not taken into account by the theory at this time.