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The current challenge in the field of nano-medicine is the design of multifunctional nano-objects effective both for the diagnosis and treatment of diseases. Here, dendronized FeO1-x@Fe3-xO4 nanoparticles with spherical, cubic, and octopode shapes and oxidized Fe3-xO4 nanocubes have been synthesized and structurally and magnetically characterized. Strong exchange bias properties are highlighted in core shell nanoparticles (NPs) due to magnetic interactions between their antiferromagnetic core and ferrimagnetic shell. Both in vitro relaxivity measurements and nuclear magnetic resonance (NMR) distribution profiles have confirmed the very good in vitro magnetic resonance imaging (Mm) properties of core shell and cubic shape NPs, especially at low concentration. This might be related to the supplementary anisotropy introduced by the exchange bias properties and the cubic shape. The high heating values of core shell NPs and oxidized nanocubes at low concentration are attributed to dipolar interactions inducing different clustering states, as a function of concentration. In vivo MRI studies have also evidenced a clustering effect at the injection point, depending on the concentration, and confirmed the very good in vivo MRI properties of core shell NPs and oxidized nanocubes in particular at low concentration. These results show that these core shell and cubic shape dendronized nano-objects are very suitable to combine MRI and hyperthermia properties at low injected doses.

Most studies on the synthesis of nanoparticles are currently focused on the controlled synthesis of new morphologies, including core-shell structures, which are expected to exhibit new magnetic properties for uses in spintronics and recording media applications. In this study, the structure, morphology, and composition of cubic-shaped nanoparticles are carefully investigated and compared to those of spherically shaped nanoparticles through the use of a combination of techniques: X-ray diffraction (XRD) and transmission electronic microscopy (TEM) combined with more sensitive techniques such as scanning transmission electron microscopy-high-angle annular dark field (STEM-HAADF) imaging, electron tomography, and holography. While spherically shaped nanoparticles (NPs) crystallize with the spinel structure, cubic-shaped NPs can be described as a cubic core of w€ustite surrounded by a spinel shell. Stresses are observed at the core-shell interface and within the spinel shell due to the epitaxial growth and oxidation mechanisms of the wüstite phase. Furthermore, magnetic measurements displayed an exchange bias coupling between the antiferromagnetic (AFM) core and the ferrimagnetic (FIM) shell structure of cubic-shaped nanoparticles. It is shown that the magnetic properties are influenced by stresses generated by the oxidation of w€ustite and, also exhibit variations depending upon the evolution of this core-shell structure as a function of the oxidation time.