Jérôme Rose

Salinity-dependent silver nanoparticle uptake and transformation by Atlantic killifish (Fundulus heteroclitus) embryos.

Abstract We assessed the biodistribution and in situ speciation of sub-lethal concentrations of citrate-coated silver nanoparticles and dissolved silver within Fundulus heteroclitus embryos. Using a thorough physico-chemical characterization, we studied the role of salinity on both uptake and in situ speciation. The Ag uptake or adsorption on the chorion was reduced by 2.3-fold for Ag NPs, and 2.9-fold for AgNO3 in estuarine water (10‰ ASW) compared to deionized water (0‰ ASW). Between 58% and 85% of the silver was localized on/in the chorion and formed patches between 20 and 80 µm. More than a physical barrier, the chorion was found to be a chemically reactive membrane controlling the in situ speciation of silver. A strong complexation of the Cit-Ag NPs with the thiolated groups of proteins or enzymes of the chorion was responsible for the oxidation of 48 ± 5% of the Ag0 into Ag(I)-S species at 0‰ ASW. However, at 10‰ ASW, the presence of Cl− ions at the surface of Ag NPs slow down this oxidation. For the dissolved silver, we observed that in deionized water 69 ± 7% of Ag+ taken up by the chorion was complexed by the thiolated molecules while the others 30 ± 3% were reduced into Ag0 likely via interaction with the hemiacetal-reducing ends of polysaccharides of the chorion.

Aggregation and sedimentation of magnetite nanoparticle clusters

Magnetite nanoparticles are redox active constituents of subsurface and corrosive environments. In this study, we characterized the aggregation and sedimentation behavior of well characterized magnetite nanoparticle clusters using dynamic light scattering (DLS), UV-vis-NIR spectroscopy, and small angle X-ray scattering (SAXS). Both unfunctionalized (NaOH-magnetite) and tetramethylammonium hydroxide (TMAOH-magnetite) surface functionalized nanoparticle clusters were employed. TMAOH-magnetite has a slightly smaller primary nanoparticle radius as determined by TEM (4 ± 0.7 nm vs. 5 ± 0.8 for NaOH-magnetite) and a smaller initial DLS determined cluster radius (<30 nm vs. 100–200 nm for NaOH-magnetite). Interestingly, in spite of its smaller initial nanoparticle cluster size, TMAOH-magnetite undergoes sedimentation more rapidly than NaOH-magnetite. This behavior is consistent with the more rapid aggregation of the smaller TMAOH-magnetite clusters as well as their lower fractal dimension, as determined by SAXS. This study illustrates that both nanoparticle cluster size and fractal dimension should be carefully considered when considering the environmental transport and fate of highly aggregated nanoparticles.

Influence of structural defects of Ge-imogolite nanotubes on their toxicity towards Pseudomonas brassicacearum

While the definition of a nanomaterial (NM) is mainly based on size, it is known that decreasing size can induce structural modifications to compensate for increased surface energy. Nevertheless, the influence of these structural modifications on NM toxicity, and in particular structural defects, is poorly studied mainly because of the difficulty in varying the crystallinity of a NM without changing any other morphological parameters. In this study, we used a single-walled alumino-germanate nanotube (Ge-imogolite) as a model, for which this can be achieved. Differences in toxicity of well-crystallized Ge-imogolite vs. Ge-imogolite presenting vacant sites towards the soil bacteria Pseudomonas brassicacearum were studied. Well crystallized tubes led to moderate toxicity attributed to a direct contact with the bacteria and the generation of reactive oxygen species, whereas tubes presenting vacant sites caused more severe toxic effects without any direct contact nor ROS generation. The bacterial growth inhibition in the presence of lacunar tubes was attributed to indirect mechanisms as their higher solubility leads to Al or Ge toxic ion release and/or to the retention of essential nutrients on the vacancies. This study highlights the close correlation between structural defects of a nanomaterial and the modulation of its mechanisms of toxicity.

Multi-scale X-ray computed tomography to detect and localize metal-based nanomaterials in lung tissues of in vivo exposed mice

In this methodological study, we demonstrated the relevance of 3D imaging performed at various scales for the ex vivo detection and location of cerium oxide nanomaterials (CeO2-NMs) in mouse lung. X-ray micro-computed tomography (micro-CT) with a voxel size from 14 µm to 1 µm (micro-CT) was combined with X-ray nano-computed tomography with a voxel size of 63 nm (nano-CT). An optimized protocol was proposed to facilitate the sample preparation, to minimize the experimental artifacts and to optimize the contrast of soft tissues exposed to metal-based nanomaterials (NMs). 3D imaging of the NMs biodistribution in lung tissues was consolidated by combining a vast variety of techniques in a correlative approach: histological observations, 2D chemical mapping and speciation analysis were performed for an unambiguous detection of NMs. This original methodological approach was developed following a worst-case scenario of exposure, i.e. high dose of exposure with administration via intra-tracheal instillation. Results highlighted both (i) the non-uniform distribution of CeO2-NMs within the entire lung lobe (using large field-of-view micro-CT) and (ii) the detection of CeO2-NMs down to the individual cell scale, e.g. macrophage scale (using nano-CT with a voxel size of 63 nm).