Nanohybrides à coeur d'Oxyde de gadolinium pour le développement de sondes IRM multimodales

Le caractère particuliaire permet de combiner plusieurs techniques de détection pour une meilleure fiabilité des résultats (imageries de fluorescence par résonance magnétique) ou d'effectuer plusieurs actions différentes mais complémentaires (diagnostic et thérapie). Sur ce dernier point, la plupart des travaux portent sur des nanoparticules à base d'or ou d'oxyde de fer. Une alternative originale aux nanoparticules dejà étudiées, pour combiner diagnostic et thérapie, pourrait concerner des nanoparticules hybrides à base d'oxyde de gadolinium : Gd203@SiOx[fluo]. Ces particules peuvent être détectées à la fois par luminescence grâce aux fluorophores organiques liés au réseau de polysiloxane enrobant le coeur et par des méthodes magnétiques, attendu que le gadolinium est largement utilisé comme agent de crontraste en IRM. De plus, son isotope 157 est cartaérisé par une forte section efficace de capture des neutrons, ces particules d'oxyde de gadolnium apparaissent comme un substitut très prometteur aux agents neutrophages actuellement utilisé en neutronthérapie. Les études ont montrées que ces nanoparticules pouvaient être suivis par des techniques d'imagerie optique et par résonance magnétique ; en in vitro, où les nanoparticules hybrides se sont relevées être des marqueurs cellulaire ; en in vivo, où, grâce à des modifications de la couche externe, ces nanoparticules ont pu être injectées par voie intraveineuse et dont leur suivis n'a pas révélé d'accumulation indésirable. Il ressort également de cette étude que les nanoparticules de Gd203@SiOx permettent d'améliorer la thérapie par capture neutroniqueLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Foam aging under free drainage analysed using associated operando techniques

Liquid foams are multi-scale structures whose structural characterization requires the combination of very different techniques. This inherently complex task is made more difficult by the fact that foams are also intrinsically unstable systems and that their properties are highly dependent on the production protocol and sample container. To tackle these issues, a new device has been developed that enables the simultaneous time-resolved investigation of foams by small-angle neutron scattering (SANS), electrical conductivity, and bubbles imaging. This device allows the characterization of the foam and its aging from nanometer up to centimeter scale on a single experiment. A specific SANS model was developed to quantitatively adjust the scattering intensity from the dry foam. Structural features such as the liquid fraction, specific surface area of the Plateau borders and inter-bubble films, thin film thickness were deduced from this analysis and some of them compared with extracted from the other applied techniques. This approach has been applied to a surfactant-stabilized liquid foam under free drainage and the underlying foam destabilization mechanisms were discussed with unprecedented detail. For example, the information extracted from the image analysis and SANS data allow for the first time to determine the disjoining pressure vs thickness isotherm in a real, draining foam

Sulfur K-edge XANES study of dihydrolipoic acid capped gold nanoparticles: dihydrolipoic acid is bound by both sulfur ends.

International audienceDihydrolipoic acid (DHLA) capped gold nanoparticles (Au@DHLA) are characterized in solid and liquid states by sulfur K-edge XANES spectroscopy; it clearly shows that DHLA is anchored to gold thanks to both sulfur ends

Synthesis, Characterization of Dihydrolipoic Acid Capped Gold Nanoparticles, and Functionalization by the Electroluminescent Luminol

The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged

Paramagnetic nanoparticles as potential MRI contrast agents: characterization, NMR relaxation, simulations and theory

Object Paramagnetic nanoparticles, mainly rare earth oxides and hydroxides, have been produced these last few years for use as MRI contrast agents. They could become an interesting alternative to iron oxide particles. However, their relaxation properties are not well understood. Materials and methods Magnetometry, 1 H and 2 H NMR relaxation results at different magnetic fields and electron paramagnetic resonance are used to investigate the relaxation induced by paramagnetic particles. When combined with computer simulations of transverse relaxation, they allow an accurate description of the relaxation induced by paramagnetic particles. Results For gadolinium hydroxide particles, both T1 and T2 relaxation are due to a chemical exchange of protons between the particle surface and bulk water, called inner sphere relaxation. The inner sphere is also responsible for T1 relaxation of dysprosium, holmium, terbium and erbium containing particles. However, for these latter compounds, T2 relaxation is caused by water diffusion in the field inhomogeneities created by the magnetic particle, the outer-sphere relaxation mechanism. The different relaxation behaviors are caused by different electron relaxation times (estimated by electron paramagnetic resonance). Conclusion These findings may allow tailoring paramagnetic particles: ultrasmall gadolinium oxide and hydroxide particles for T1 contrast agents, with shapes ensuring the highest surface-to-volume ratio. All the other compounds present interesting T2 relaxation performance at high fields. These results are in agreement with computer simulations and theoretical predictions of the outer-sphere and static dephasing regime theories. The T2 efficiency would be optimum for spherical particles of 40–50 nm radius.Fil: Vuong, Quoc Lam. University of Mons. Biological Physics Department; BélgicaFil: Van Doorslaer, Sabine. Universiteit Antwerpen; BélgicaFil: Bridot, Jean Luc. Laval University; Canadá. Université Lava. Centre de Recherche sur les Matériaux Avancés; BélgicaFil: Argante, Corradina. University of Mons. Biological Physics Department; BélgicaFil: Alejandro, Gabriela. Universiteit Antwerpen; Bélgica. Comision Nacional de Energia Atomica. Centro Atomico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hermann, Raphaël. Universite de Liege; Bélgica. Westfalische Wilhelms Universitat. Institut Fur Festkorpertheorie; AlemaniaFil: Disch, Sabrina. Institut für Festkörperforschung; AlemaniaFil: Mattea, Carlos. Universität Ilmenau. Fakultät für Mathematik und Naturwissenschaften; AlemaniaFil: Stapf, Siegfried. Universität Ilmenau. Fakultät für Mathematik und Naturwissenschaften; AlemaniaFil: Gossuin, Yves. University of Mons. Biological Physics Department; Bélgic

Hybrid gadolinium oxide nanoparticles: multimodal contrast agents for in vivo imaging.

International audienceLuminescent hybrid nanoparticles with a paramagnetic Gd2O3 core were applied as contrast agents for both in vivo fluorescence and magnetic resonance imaging. These hybrid particles were obtained by encapsulating Gd2O3 cores within a polysiloxane shell which carries organic fluorophores and carboxylated PEG covalently tethered to the inorganic network. Longitudinal proton relaxivities of these particles are higher than the positive contrast agents like Gd-DOTA which are commonly used for clinical magnetic resonance imaging. Moreover these particles can be followed up by fluorescence imaging. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in lungs and liver

Modulation of bacterial multicellularity via spatio-specific polysaccharide secretion

International audienceThe development of multicellularity is a key evolutionary transition allowing for differentiation of physiological functions across a cell population that confers survival benefits; among uni-cellular bacteria, this can lead to complex developmental behaviors and the formation of higher-order community structures. Herein, we demonstrate that in the social δ-proteobac-terium Myxococcus xanthus, the secretion of a novel biosurfactant polysaccharide (BPS) is spatially modulated within communities, mediating swarm migration as well as the formation of multicellular swarm biofilms and fruiting bodies. BPS is a type IV pilus (T4P)-inhibited acidic polymer built of randomly acetylated β-linked tetrasaccharide repeats. Both BPS and exopolysaccharide (EPS) are produced by dedicated Wzx/Wzy-dependent polysaccharide-assembly pathways distinct from that responsible for spore-coat assembly. While EPS is preferentially produced at the lower-density swarm periphery, BPS production is favored in the higher-density swarm interior; this is consistent with the former being known to stimulate T4P retraction needed for community expansion and a function for the latter in promoting initial cell dispersal. Together, these data reveal the central role of secreted polysaccharides in the intricate behaviors coordinating bacterial multicellularity