Maria Francesca Casula

Biological applications of magnetic nanoparticles.

In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.

Multifunctional Nanoparticles for Dual Imaging

For imaging with different modalities, labels, which provide contrast for all modalities, are required. Colloidal nanoparticles composed out of an inorganic core and a polymer shell offer progress in this direction. Both, the core and the polymer shell, can be synthesized to be fluorescent, magnetic, or radioactive. When different cores are combined with different polymer shells, different types of particles for dual imaging can be obtained, as for example, fluorescent cores with radioactive polymer shells. Properties and perspectives of such nanoparticles for multimodal imaging are discussed.

PEG-templated mesoporous silica nanoparticles exclusively target cancer cells

Mesoporous silica nanoparticles (MSNs) have been proposed as DNA and drug delivery carriers, as well as efficient tools for fluorescent cell tracking. The major limitation is that MSNs enter cells regardless of a target-specific functionalization. Here we show that non functionalized MSNs, synthesized using a PEG surfactant-based interfacial synthesis procedure, do not enter cells, while a highly specific, receptor mediated, cellular internalization of folic acid (FOL) grafted MSNs (MSN-FOL), occurs exclusively in folate receptor (FR) expressing cells. Neither the classical clathrin pathway nor macropinocytosis is involved in the MSN endocytic process, while fluorescent MSNs (MSN-FITC) enter cells through aspecific, caveolae-mediated, endocytosis. Moreover, internalized particles seem to be mostly exocytosed from cells within 96 h. Finally, cisplatin (Cp) loaded MSN-FOL were tested on cancerous FR-positive (HeLa) or normal FR-negative (HEK293) cells. A strong growth arrest was observed only in HeLa cells treated with MSN-FOL-Cp. The results presented here show that our mesoporous nanoparticles do not enter cells unless opportunely functionalized, suggesting that they could represent a promising vehicle for drug targeting applications.

Formation and cation distribution in supported manganese ferrite nanoparticles: an X-ray absorption study

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) techniques at both Fe and Mn K-edges were used to investigate the formation of MnFe(2)O(4) nanoparticles embedded in a silica aerogel matrix as a function of calcination temperature (at 450, 750 and 900 degrees C). Up to 450 degrees C, two separated highly-disordered phases of iron and manganese are present. With increasing the temperature (to 750 and 900 degrees C), the structure of aerogel nanoparticles becomes progressively similar to that of the spinel structure MnFe(2)O(4) (jacobsite). Quantitative determination of cations distribution in the spinel structure shows that aerogels calcined at 750 and 900 degrees C have a degree of inversion i = 0.20. A pure jacobsite sample synthesised by co-precipitation and used as a reference compound shows a much higher degree of inversion (i = 0.70). The different distribution of iron and manganese cations in the octahedral and tetrahedral sites in pure jacobsite and in the aerogels can be ascribed to partial oxidation of Mn(2+) to Mn(3+) in pure jacobsite, confirmed by XANES analysis, probably due to the synthesis conditions.

Physical and Chemical Lipase Adsorption on SBA‐15: Effect of Different Interactions on Enzyme Loading and Catalytic Performance

Immobilization of Pseudomonas fluorescens lipase (Pfl) on the chemically modified, or unmodified, surface of SBA‐15 mesoporous silica has been achieved. X‐ray diffraction (XRD), transmission electron microscopy (TEM), and N2 physisorption are used to monitor the effect of surface functionalization on the structural and textural features of the SBA‐15 silica support. The enzyme loading strongly depends on the type of enzyme–support interaction, the maximal loading of the chemisorbed lipase being about twice that of the physisorbed (502 and 256 mgprotein 

Growth of colloidal nanoparticles of group II–VI and IV–VI semiconductors on top of magnetic iron–platinum nanocrystals

{{\rm g}{{- 1\hfill \atop {\rm support}\hfill}}}

Synthesis and microstructure of manganese ferrite colloidal nanocrystals

respectively). The resulting biocatalysts, regardless of the different loading, are tested with a hydrolytic catalytic assay. Despite the lower loading, the physically immobilized Pfl is more active than that which is chemically immobilized. Both biocatalysts are also active in a green process for biodiesel production, leading to almost full conversion of sunflower oil and ethanol into the corresponding ethyl esters after about 7 h at 30 °C, atmospheric pressure, and in solvent‐free conditions. Recycling experiments showed that the chemically immobilized Pfl was still active after twenty reaction cycles whereas the physically immobilized Pfl lost its activity after the tenth cycle.

4-Methylpentan-2-ol dehydration over zirconia catalysts prepared by sol-gel

Colloidal hybrid nanoparticles with blebs of II–VI and IV–VI particles on top of FePt particles were successfully grown. Whereas in the case of XE = CdS, ZnS, PbS and CdSe, FePt–XE dimer structures were successfully obtained, the growth failed for XE = ZnSe, PbSe. Structural, magnetic, and optical analysis of the structures revealed a moderate influence of the semiconductor domain on the magnetic properties of the FePt core particle, which can be ascribed to the effect of annealing conditions, atom diffusion and compositional variations during heterostructure formation. On the other hand, we report a significant fluorescence quenching of the semiconductor bleb due to the underlying FePt particle.

Structural characterization study of FeCo alloy nanoparticles in a highly porous aerogel silica matrix

The atomic level structure of a series of monodisperse single crystalline nanoparticles with a magnetic core of manganese ferrite was studied using X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) techniques at both the Fe and Mn K-edges, and conventional and high resolution transmission electron microscopy (TEM and HRTEM). In particular, insights on the non-stoichiometry and on the inversion degree of manganese ferrite nanocrystals of different size were obtained by the use of complementary structural and spectroscopic characterization techniques. The inversion degree of the ferrite nanocrystals, i.e. the cation distribution between the octahedral and tetrahedral sites in the spinel structure, was found to be much higher (around 0.6) than the literature values reported for bulk stoichiometric manganese ferrite (around 0.2). The high inversion degree of the nanoparticles is ascribed to the partial oxidation of Mn(2+) to Mn(3+) which was evidenced by XANES, leading to non-stoichiometric manganese ferrite.

Iron oxide–silica aerogel and xerogel nanocomposite materials

Zirconia samples have been prepared from xerogels and aerogels obtained using zirconium n-propoxide as precursor. Structure and texture have been investigated by X-ray diffraction, thermal analysis, transmission electron microscopy, nitrogen adsorption/desorption. Surface acidity and basicity have been assessed by adsorption microcalorimetry, using ammonia and carbon dioxide as probe molecules. 4-Methylpentan-2-ol dehydration has been tested at atmospheric pressure in a fixed-bed flow microreactor. The xerogel gives tetragonal zirconia upon calcination, during which a mesoporous system is formed. The crystal phase depends on the presence of oxygen during the cooling step in the case of the aerogel, whose texture is partially retained upon calcination. Both kinds of catalysts have well-balanced concentrations of acid and base sites, but the acid sites are weaker in comparison with the basic ones. At 603 K the initial conversion of 4-methylpentan-2-ol over the calcined xerogel and aerogel is 45 and 63%, respectively; the selectivity to 4-methylpent-1-ene is 77% for both. The occurrence of an E2-like mechanism with the activated complex having a marked carbanionic character seems probable. The aerogel catalyst is quite stable during operation, whereas changes in activity and selectivity are observed for the xerogel catalyst.