Pedro Tartaj

The preparation of magnetic nanoparticles for applications in biomedicine

This review is focused on describing state-of-the-art synthetic routes for the preparation of magnetic nanoparticles useful for biomedical applications. In addition to this topic, we have also described in some detail some of the possible applications of magnetic nanoparticles in the field of biomedicine with special emphasis on showing the benefits of using nanoparticles. Finally, we have addressed some relevant findings on the importance of having well-defined synthetic routes to produce materials not only with similar physical features but also with similar crystallochemical characteristics.

Progress in the preparation of magnetic nanoparticles for applications in biomedicine

This review summarizes recent advances in synthesis routes for quickly and reliably making and functionalizing magnetic nanoparticles for applications in biomedicine. We put special emphasis on describing synthetic strategies that result in the production of nanosized materials with well-defined physical and crystallochemical characteristics as well as colloidal and magnetic properties. Rather than grouping the information according to the synthetic route, we have described methods to prepare water-dispersible equiaxial magnetic nanoparticles with sizes below about 10 nm, sizes between 10 and 30 nm and sizes around the monodomain–multidomain magnetic transition. We have also described some recent examples reporting the preparation of anisometric nanoparticles as well as methods to prepare magnetic nanosized materials other than iron oxide ferrites, for example Co and Mn ferrite, FePt and manganites. Finally, we have described examples of the preparation of multicomponent systems with purely inorganic or organic–inorganic characteristics.

Zircon formation from amorphous spherical ZrSiO4 particles obtained by hydrolysis of aerosols

A procedure for the preparation of SiO2·ZrO2 spherical particles, based on the hydrolysis of liquid aerosols is described. A mixture of tetraethylortho-silicate (TEOS) and zirconium n-propoxide with the proper stoichiometry (Zr/Si atomic ratio = 1) was used as a liquid precursor. The alkoxide mixture had to be partially hydrolysed before aerosol generation in order to obtain solids with a zircon composition. The as-prepared powders consisted of particles in the micrometre range with an amorphous character. Energy dispersive X-ray spectroscopy (EDX), infrared (i.r.) and nuclear magnetic resonance (NMR) analyses indicated the existence of a good compositional homogeneity and a large number of Si-O-Zr bonds in the sample. Calcination of the powder up to 950°C gave rise to the segregation of silica and the crystallization of tetragonal zirconia, which transformed into the monoclinic phase after heating at 1300°C. Crystallization of zircon started on calcination at 1450°C; it was accompanied by the formation of some cristobalite. The complete transformation of the sample into zircon took place after prolonged heating (20 h) at 1500°C.

Multifunctional Response of Anatase Nanostructures Based on 25 nm Mesocrystal‐Like Porous Assemblies

Financial support from Spain Ministerio de Ciencia e Innovacion under projects MAT2008-03224 and MAT2008-03182 is acknowledged.

Infrared optical properties of zircon

We have measured the infrared reflectance spectrum of the ordinary ray of a zircon single crystal in order to determine the optical constants of the Eu modes. With the obtained data and the optical parameters corresponding to the A2u modes (extraordinary ray) taken from literature, we have analyzed the absorption spectra of zircon powders by using the Maxwell-Garnett Theory (MGT) and the Effective Medium Theory (EMT), which take into account the effects of the shape and aggregation state of the particles. This analysis showed that although MGT can account for the main vibrational zircon features, EMT seems a more appropriate approach to interpret the powder spectra since it gives a more accurate estimation of the particle aggregation effects. From the above study, the assignment of the bands in the infrared powder spectrum of zircon has also been carried out.

The formation of zircon from amorphous ZrO2 · SiO2 powders

The different factors affecting the mechanism of zircon formation from amorphous ZrO2 · SiO2 powders have been studied. It was shown that zircon was formed by solid state reaction between tetragonal zirconia and silica (amorphous and cristobalite). The previously suggested Hedvall effect associated with the crystallization of amorphous silica into cristobalite did not play any role in this reaction. A high degree of Si-Zr mixing in the starting amorphous powders did not affect the mechanism of zircon formation, but speeded up the reaction rate due to the small particle size of the zirconia and silica particles segregated previously to zircon formation. It was also found that the formation reaction was retarded by the presence of carbonaceous species coming from the alkoxide precursors, which were probably retained at grain boundaries after calcination, acting as a diffusion barrier. These factors can explain the observed differences in the temperatures of zircon formation previously reported.

Signatures of clustering in superparamagnetic colloidal nanocomposites of an inorganic and hybrid nature.

The individual and co-operative properties of inorganic and hybrid superparamagnetic colloidal nanocomposites that satisfy all the requirements of magnetic carriers in the biosciences and/or catalysis fields are been studied. Essential to the success of this study is the selection of suitable synthetic routes (aerosol and nanocasting) that allow the preparation of materials with different matrix characteristics (carbon, silica, and polymers with controlled porosity). These materials present magnetic properties that depend on the average particle size and the degree of polydispersity. Finally, the analysis of the co-operative behavior of samples allows for the detection of signatures of clustering, which are closely related to the textural characteristics of samples and the methodology used to produce the magnetic carriers.

The effects of the NaF flux on the oxidation state and localisation of praseodymium in Pr-doped zircon pigments

Abstract The role that NaF plays in the preparation of Pr-doped zircon pigments was studied through the analysis of the nature and localisation of the Pr cations into the zircon matrix in samples prepared in the absence and in the presence of NaF. As previously observed, the addition of NaF caused a decrease of the minimum temperature required for zircon formation from 1400 to 1100°C, and an increase of the yellow colour intensity. In the absence of NaF, the Pr cations mainly presented a threefold oxidation state, being located out of the zircon lattice as Pr2Zr2O7, whereas in the presence of this flux, most of the Pr cations showed a fourfold valence and formed a solid solution with the zircon lattice, which was then the main responsible for the stronger yellow colour observed in this case. After heating this pigment at 1400°C, we detected an exsolution of the Pr (IV) cations as Pr8Si6O24 which was accompanied by a decrease of the yellow colour intensity. Therefore, it was concluded that the main role of NaF in the preparation of yellow Pr-zircon pigments is to decrease the temperature of zircon formation to the range in which the chromophore responsible for the bright yellow colour, i.e. the Pr (IV)-zircon solid solution, is stable.

Fabrication of mesoporous SiO2–C–Fe3O4/γ–Fe2O3 and SiO2–C–Fe magnetic composites

A synthetic method for the fabrication of silica-based mesoporous magnetic (Fe or iron oxide spinel) nanocomposites with enhanced adsorption and magnetic capabilities is presented. The successful in situ synthesis of magnetic nanoparticles is a consequence of the incorporation of a small amount of carbon into the pores of the silica, this step being essential for the generation of relatively large iron oxide magnetic nanocrystals ( approximately 10+/-3nm) and for the formation of iron nanoparticles. These composites combine good magnetic properties (superparamagnetic behaviour in the case of SiO(2)-C-Fe(3)O(4)/gamma-Fe(2)O(3) samples) with a large and accessible porosity made up of wide mesopores (>9nm). In the present work, we have demonstrated the usefulness of this kind of composite for the adsorption of a globular protein (hemoglobin). The results obtained show that a significant amount of hemoglobin can be immobilized within the pores of these materials (up to 180mgg(-1) for some of the samples). Moreover, we have proved that the composite loaded with hemoglobin can be easily manipulated by means of an external magnetic field.

Iron Oxide Nanosized Clusters Embedded in Porous Nanorods: A New Colloidal Design to Enhance Capabilities of MRI Contrast Agents

Development of nanosized materials to enhance the image contrast between the normal and diseased tissue and/or to indicate the status of organ functions or blood flow is essential in nuclear magnetic resonance imaging (MRI). Here we describe a contrast agent based on a new iron oxide design (superparamagnetic iron oxide clusters embedded in antiferromagnetic iron oxide porous nanorods). We show as a proof-of-concept that aqueous colloidal suspensions containing these particles show enhanced-proton relaxivities (i.e., enhanced MRI contrast capabilities). A remarkable feature of this new design is that large scale production is possible since aqueous-based routes are used, and porosity and iron oxide superparamagnetic clusters are directly developed from a single phase. We have also proved with the help of a simple model that the physical basis behind the increase in relaxivities lies on both the increase of dipolar field (interactions within iron oxide clusters) and the decrease of proton-cluster distance (porosity favors the close contact between protons and clusters). Finally, a list of possible steps to follow to enhance capabilities of this contrast agent is also included (partial coating with noble metals to add extra sensing capacity and chemical functionality, to increase the amount of doping while simultaneously carrying out cytotoxicity studies, or to find conditions to further decrease the size of the nanorods and to enhance their stability).