Lorentz microscopy sheds light on the role of dipolar interactions in magnetic hyperthermia.

Monodispersed Fe3O4 nanoparticles with comparable size distributions have been synthesized by two different synthesis routes, co-precipitation and thermal decomposition. Thanks to the different steric stabilizations, the described samples can be considered as a model system to investigate the effects of magnetic dipolar interactions on the aggregation states of the nanoparticles. Moreover, the presence of magnetic dipolar interactions can strongly affect the nanoparticle efficiency as a hyperthermic mediator. In this paper, we present a novel way to visualize and map the magnetic dipolar interactions in different kinds of nanoparticle aggregates by the use of Lorentz microscopy, an easy and reliable in-line electron holographic technique. By exploiting Lorentz microscopy, which is complementary to the magnetic measurements, it is possible to correlate the interaction degrees of magnetic nanoparticles with their magnetic behaviors. In particular, we demonstrate that Lorentz microscopy is successful in visualizing the magnetic configurations stabilized by dipolar interactions, thus paving the way to the comprehension of the power loss mechanisms for different nanoparticle aggregates.

Composite multifunctional nanostructures based on ZnO tetrapods and superparamagnetic Fe3O4 nanoparticles.

A nanocomposite material is obtained by coupling superparamagnetic magnetite nanoparticles (Fe3O4 NP) and vapor phase grown zinc oxide nanostructures with 'tetrapod' morphology (ZnO TP). The aim is the creation of a multifunctional material which retains the attractive features of ZnO (e.g. surface reactivity, strong UV emission, piezoelectricity) together with added magnetism. Structural, morphological, optical, magnetic and functional characterization are performed. In particular, the high saturation magnetization of Fe3O4 NP (above 50 A m(2) kg(-1)), the strong UV luminescence and the enhanced photocatalytic activity of coupled nanostructures are discussed. Thus the nanocomposite turns out to be suitable for applications in energy harvesting and conversion, gas- and bio-sensing, bio-medicine and filter-free photocatalysis.

Magnetic solid-phase extraction based on diphenyl functionalization of Fe3O4 magnetic nanoparticles for the determination of polycyclic aromatic hydrocarbons in urine samples.

Superparamagnetic Fe(3)O(4) diphenyl nanoparticles were prepared according to a solvothernal procedure and characterized by X-ray diffraction, infrared spectroscopy, surface area measurements, scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The magnetic phases present in the nanoparticle samples were analyzed by thermomagnetic analysis and the samples' magnetic properties were studied by vibrating sample magnetometry. The resulting nanoparticles having an average diameter of 200 nm were then used as solid-phase extraction sorbent for the determination of polycyclic aromatic hydrocarbons in urine samples. Method validation proved the feasibility of the developed beads for the quantitation of the investigated analytes at trace levels obtaining lower limit of quantitation values in the ng/l range. A good precision with coefficients of variations always lower than 15% was obtained. Finally, the superior extraction performance of the synthesized nanoparticles with respect to commercially available beads was proved.