Low toxicity superparamagnetic magnetite nanoparticles: One-pot facile green synthesis for biological applications.

Superparamagnetic magnetite nanoparticles have been synthesized by a highly reproducible polyvinyl alcohol (PVA)-based modified sol-gel process using water as the only solvent. The synthesis method has proven to be effective, time and cost saving and environmental friendly, resulting in PVA-coated magnetite nanoparticles as direct product from the synthesis, without any special atmosphere or further thermal treatment. X-ray diffraction and transmission electron microscopy revealed that the biocompatible PVA-coating prevents the nanoparticle agglomeration, giving rise to spherical crystals with sizes of 6.8nm (as-cast) and 9.5nm (heat treated) with great control over size and shape with narrow size distribution. Complementary compositional and magnetic characterizations were employed in order to study the surface chemistry and magnetic behavior of the samples, respectively. Cytotoxicity endpoints including no observed adverse effect concentration (NOAEC), 50% lethal concentration (LC50) and total lethal concentration (TLC) of the tested materials on cell viability were determined after 3, 24 and 48h of exposure. The PVA coating improved the biocompatibility of the synthesized magnetite nanoparticles showing good cell viability and low cytotoxicity effects on the MTT assay performed on BHK cells. Preliminary assessment of nanoparticles in vivo effects, performed after 48h on Balb/c mice, exposed to a range of different sub-lethal doses, showed their capacity to penetrate in liver and kidneys with no significant morphological alterations in both organs.

Dimensionality tuning of the electronic structure in Fe3Ga4 magnetic materials.

This work reports on the dimensionality effects on the magnetic behavior of Fe3Ga4 compounds by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results show that reducing the Fe3Ga4 dimensionality, via nanowire shape, intriguingly modifies its electronic structure. In particular, the bulk system exhibits two transitions, a ferromagnetic (FM) transition temperature at T1 = 50 K and an antiferromagnetic (AFM) one at T2 = 390 K. On the other hand, nanowires shift these transition temperatures, towards higher and lower temperature for T1 and T2, respectively. Moreover, the dimensionality reduction seems to also modify the microscopic nature of the T1 transition. Instead of a FM to AFM transition, as observed in the 3D system, a transition from FM to ferrimagnetic (FERRI) or to coexistence of FM and AFM phases is found for the nanowires. Our results allowed us to propose the magnetic field-temperature phase diagram for Fe3Ga4 in both bulk and nanostructured forms. The interesting microscopic tuning of the magnetic interactions induced by dimensionality in Fe3Ga4 opens a new route to optimize the use of such materials in nanostructured devices.