Magnetic nanoparticle design for medical applications

Magnetic nanoparticles have attracted attention because of their current and potential usefulness as contrast agents for magnetic resonance imaging (MRI) or colloidal mediators for cancer magnetic hyperthermia. This contribution examines these in vivo applications through an understanding of the involved problems and the current and future possibilities for resolving them. A special emphasis is made on magnetic nanoparticle requirements from a physical viewpoint (e.g. relaxivity for MRI and specific absorption rate for hyperthermia), the factors affecting their biodistribution and the solutions envisaged for enhancing their half-life in the blood compartment and targeting tumour cells. Then, the synthesis strategies developed in our group are presented and focused on covalent platforms capable to be tailor-derivatised by surface molecular chemistry. The opportunity of using more complex oxides than conventional magnetite for controlling the in vivo temperature is also discussed.     

Development of the continuously variable volume reactor for flow injection analysis: Part 1. Design, capabilities and testing

A new apparatus for mixing sample and reagent in flow injection analysis (FIA) is described. The continuously variable volume reactor (CVVR) replaces the conventional mixing coil in a flow injection (FI) manifold to provide mixing and dilution. A linear actuator motor allows control of the chamber volume via LabVIEW software. The chamber volume can be incremented in steps of 1 μl over the range 68-1704 μl. In addition, the chamber has an integral variable-speed stirring unit that is also under computer control. Experiments were performed to evaluate the dispersion characteristics of this new device, evaluate the volume reproducibility, and understand the mixing characteristics. Use of the chamber is shown in the determination of iron(II) in pond water, and in NIST SRM 1643d with excellent results and a detection limit of 3.7 μg/l iron(II). Advantages of the CVVR and future research activities using the device are discussed.     

Etude cristallographique et par effet Mössbauer du fluorure ferrimagnétique Na5Fe3F14γ

The structure of ferrimagnetic γ-Na₅Fe₃F₁₄ has been determined by single-crystal X-ray diffraction. The cell is tetragonal with space group P4₂2₁2 and parameters a = 7.345 ± 0.007 Å and c = 10.400 ± 0.007 Å. The iron atoms occupy a twofold and a fourfold position in the lattice and are octahedrally surrounded by fluorines. These octahedra share corners and form two-dimensional layers of formula (Fe₃F₁₄)^5n?_n. The Mössbauer spectra were measured from 4.2 to 293°K and the results are discussed in terms of the position and environment of iron atoms in the lattice.     

Planar defects in β-alumina

Sodium β-alumina crystals were elaborated by melting of a mixture of Na₂CO₃ and Al₂O₃ or by PbO flux evaporation and were studied by transmission electron microscopy. They exhibit regular planar defects lying in the {11.0} prismatic planes. These defects are described as antiphase boundaries for the cationic sublattice with fault vectors $\text{1}\text{2}\text{〈10.0〉}$ (such faults do not affect the anionic sublattice). As a consequence it would be interesting to study precisely the structure of the sodium β cationic lattice in the vicinity of the melting point.     

The German bakery waste incident; use of a combined approach of screening and confirmation for dioxins in feed and food

During the last six years several incidents have occurred with dioxins in feed, stressing the need for rapid screening methods for these compounds. The most recent incident was the contamination of bakery waste used for animal feed due to the use of waste wood for drying of the material. In addition to Germany, the material was also shipped to the Netherlands. Levels up to 12 ng TEQ/kg have been detected, being about 15 times over the current limit of 0.75 ng TEQ/kg. In the Netherlands a combined strategy of screening with the CALUX-bioassay and the HRGC/HRMS confirmatory method was used to rapidly control the incident. Pigs were contaminated by the incident but only to a very limited extent. Despite the rather low limits for pig meat, the CALUX bioassay showed excellent performance, once again confirming the value of this assay.     

Assessment of the Nd/U ratio for the quantification of neodymium in UO2

The secondary ion energy spectrum of uranium depends on the experimental conditions, which is a problem for the application of a relative sensitivity factor (RSF) procedure for the measurement of the Nd concentration in UO₂. This is interpreted as due to the dependence of the sputtering and ionisation yields of uranium on the oxidation state of the surface. Three experimental procedures are being tested to cope with this difficulty.     

Optical losses and absorption cross-section of silicon nanocrystals

 Si-rich silicon oxide and SiO₂ (SRSO)/SiO₂ multilayer (ML) samples were grown by reactive magnetron sputtering and then annealed at high temperature to induce the formation of Si-nc with mean size of 3-4 nm and density of about 3.5×10¹⁸ cm⁻³ as deduced from high resolution TEM micrographs. Refractive index and thickness have been determined by m-line measurements, which have shown a birefringence of about 1.5% due to the ML structure. Rib-loaded waveguides have been fabricated to measure propagation losses in the visible-infrared range. The analysis of the different contributions to optical losses such as Mie scattering and scattering due to waveguide roughness has allowed us to isolate the contribution due to the absorption losses and thus to extract the absorption cross-section at different wavelengths. Values of about 3.5×10⁻¹⁸ cm² have been found at 830 nm, increasing with decreasing of the wavelength.     

Sur un nouvel hexafluorure de nickel trivalent de formule Li3NiF6.

The action of 70 bar of fluorine at 500°C on a mixture of lithium and nickel +II fluorides leads to a Li₃NiF₆ phase isostructural with α-Li₃AlF₆. The magnetic measurements characterize at low temperature the low spin configuration of nickel +III (d⁷), which tends to a high spin configuration with increasing temperature.     

Interactions magnetiques hyperfines pour les atomes d'impurete 121Sb5+ dans FeF3

The Mössbauer spectra of ¹²¹Sb⁵⁺ in the antiferromagnetic FeF₃ composition indicates the presence of a magnetic transfer region amongst the nucleus of the impurities of the antimony: H_eff(77°K) = 110 ± 15 kOe. The comparison of the value of H_eff observed on the nucleus of ¹¹⁹Sn⁴⁺ and of ¹²¹Sb⁵⁺ in the matrix of FeF₃ suggests a different mechanism of transference of the magnetic hyperfine region in relation to the position of the same pair of Mössbauer isotopes in the midst of the oxygen matrix.