Addressing the Effect of Magnetic Particle Hyperthermia Application on the Composition and Spatial Distribution of Iron Oxide Nanoparticles Using X ray Spectroscopic Techniques

Iron oxide magnetic nanoparticles MNPs are promising candidates in magnetic particle hyperthermia MPH applications. However, MPH often initiates the oxidation process of magnetite to maghemite, thus modifying the magnetic properties and heating efficiency of the MNPs. Here, we report on the degree of oxidation of iron oxide MNPs in parallel to their spatial distribution in order to understand the oxidation behavior and extent of aggregation upon MPH application. The micrometric spatial distribution of the MNPs in an agarose gel matrix was addressed using two dimensional amp; 956; X ray fluorescence XRF elemental mapping. It is demonstrated that both the size and MPH application disturb their homogenous distribution. The most pronounced changes are detected in the smallest 10 mn MNPs, where MPH prompts the creation of extended aggregates. Surface and bulk properties of the MNPs are addressed using X ray absorption fine structure XAFS spectroscopies. XAFS measurements using soft X rays reveal the complete transformation of the MNP surface from magnetite to maghemite to a depth of ca. 4.5 nm, independently of their size. The implemented hard X ray spectroscopic methods reveal a core shell Fe3O4 amp; 947; Fe2O3 structure. The surface shell becomes progressively thicker as the diameter of the MNP increases, yet the extent of surface oxidation is less pronounced in the larger MNPs. The degree of oxidation of the MNPs is also a function of the MPH applications and is enhanced due to the thermal load suffered during the MPH treatmen