Sophie Neveu

Synthesis of very fine maghemite particles

Abstract The effect of citrate ions on the growth of magnetite particles is investigated. ‘Ultrafine’ particles have been obtained (diameter of the order of 20 A) that were converted to maghemite. The characterisation of the maghemite particles by various techniques (X-ray diffraction, transmission electron microscopy, magnetic measurements) is described.

Different Microtubule Motors Move Early and Late Endocytic Compartments

Important progress has been made during the past decade in the identification of molecular motors required in the distribution of early and late endosomes and the proper trafficking along the endocytic pathway. There is little direct evidence, however, that these motors drive movement of the endosomes. To evaluate the contributions of kinesin‐1, dynein and kinesin‐2 to the movement of early and late endosomes along microtubules, we made use of a cytosol‐free motility assay using magnetically isolated early and late endosomes as well as biochemical analyses and live‐cell imaging. By making use of specific antibodies, we confirmed that kinesin‐1 and dynein move early endosomes and we found that kinesin‐2 moves both early and late endosomes in the cell‐free assay. Unexpectedly, dynein did not move late endosomes in the cell‐free assay. We provide evidence from disruption of dynein function and latrunculin A treatment, suggesting that dynein regulates late endosome movement indirectly, possibly through a mechanism involving the actin cytoskeleton. These data provide new insights into the complex regulation of endosomes’ motility and suggest that dynein is not the major motor required to move late endosomes toward the minus end of microtubules.

MONODISPERSE MAGNETIC NANOPARTICLES : PREPARATION AND DISPERSION IN WATER AND OILS

Nanometric maghemite and cobalt ferrite particles are chemically synthesized. The process produces particles polydisperse in size. The positive charges of their surface allow one to disperse them in aqueous acidic solutions and to obtain dispersions stabilized through electrostatic repulsions. Increasing acid concentration (in the range 0.1 to 0.5 mol.L −1 ), interparticles repulsions are screened and phase transitions are induced. Using this phenomenon, we describe a two-step size sorting process, in order to get significant amounts of nanometric monosized particles (with diameters monitored between typically 6 and 13 nm). As the surface of the latter is not modified by the size sorting process, usual procedures are used to disperse them in several aqueous or oily media.

The magnetic fluid for heat transfer applications

Abstract Real-time visual observation of boiling water-based and ionic magnetic fluids (MFs) and heat transfer characteristics in heat pipe using ionic MF stabilized by citrate ions (JC-1) as working liquid are reported. Irrespective of the presence or absence of magnetic field water-based MF degraded during boiling. However, the degradation of JC-1 was avoided by heating the fluid in magnetic field. Furthermore, the heat transfer capacity of JC-1 heat pipe under applied magnetic field was enhanced over the no field case.

Magneto-optical waveguides made of cobalt ferrite nanoparticles embedded in silica/zirconia organic-inorganic matrix

This paper describes a way to develop magneto-optical waveguides via sol-gel process. They are made of cobalt ferrite nanoparticles embedded in a silica/zirconia matrix. Thin films are coated on glass substrate using the dip-coating technique. Annealing and UV treatment are applied to finalize sample preparation. Therefore, planar waveguides combining magneto-optical properties with a low refractive index (≈1,5) are obtained. M-lines and free space ellipsometry measurements show a specific Faraday rotation of 250°/cm and a modal birefringence of 1×10−4 at 820 nm. Thus, the mode conversion efficiency can reach a maximum value around 56%.

Synthesis of Goethite by Separation of the Nucleation and Growth Processes of Ferrihydrite Nanoparticles Using Microfluidics

Microfluidic synthesis is used to form nanoparticles by separate nucleation and growth processes using two microreactors (see picture) operating under different temperature and flow conditions. Ferrihydrite nanoparticles precipitated in the first microreactor are aged under continuous flow in a second microtubular reactor, leading to goethite nanoparticles. TMAOH = tetramethylammonium hydroxide.

Synthesis of cobalt ferrite nanoparticles in continuous-flow microreactors

High quality CoFe2O4 nanoparticles were synthesized only in 16 min, continuously in two coupled microreactors. The first microreactor induced the fast homogenization of the reagents mixture at ambient temperature so Fe3+ and Co2+ hydroxides precipitate, while a second microreactor heated at 98 °C allowed the fast aging and the evolution of amorphous hydroxides into faceted and crystalline CoFe2O4.

Nanocomposite systems based on gold nanoparticles and thiometalates. From colloids to networks

A new nanocomposite system based on gold nanoparticles and thiometalates is described. According to the metalate species, WS42¬ or WS2O22¬, and to the experimental conditions, two sizes of particles are obtained (d = 2 or 5 nm). These particles lead either to stable colloidal solutions or irreversible micrometric spherical aggregates of nanoparticles cemented by WS42¬. Energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to fully characterize the different composite systems.

Different localizations of hydrophobic magnetic nanoparticles within vesicles trigger their efficiency as magnetic nano-heaters

The reverse phase evaporation (REV) and the multiple emulsion (ME) process are used to encapsulate hydrophobic magnetic nanoparticles (MNPs) within vesicles. The effect of the size distribution of the nanoparticles on their location in the liposomes has been observed by transmission electron microscopy: the small ones are in the inner core of the vesicles while the larger ones are found to be located at the membrane level. The influence of the confinement of hydrophobic nanoparticles inside vesicles on their subsequent magnetic properties (relaxometry, heating capacity) has been studied.

Hybrid magneto-optical mode converter made with a magnetic nanoparticles-doped SiO2/ZrO2 layer coated on an ion-exchanged glass waveguide

This paper describes the possibility to achieve a TE-TM mode conversion in a magneto-optical hybrid waveguide operating at λ = 1550 nm. This hybrid device is made by coating a SiO2/ZrO2 layer doped with magnetic nanoparticles on an ion-exchanged glass waveguide. Soft annealing (90 °C) and UV treatment, both compatible with the ion exchange process, have been implemented to finalize the magneto-optical film. Optical characterizations that have been carried out demonstrated the efficiency of these hybrid structures in terms of lateral confinement and mode conversion. Indeed, TE to TM mode conversion has been observed when a longitudinal magnetic field is applied to the device. The amount of this conversion is discussed taking into account the distribution of light between the layer and the guide, and the modal birefringence of the structure.