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International audience; Oxidation of unsaturated lipids promotes important changes in the lipid packing or phase separation in cellular membranes or membrane models. Here, we study by Atomic Force Microscopy (AFM) the behavior of oxidized lipids in Langmuir-Blodgett (LB) films by using two strategies : either following the evolution of LB films of POPC (palmitoyloleoyl-phosphatidylcholine) naturally ageing in contact of atmospheric oxygen, or incorporating a known amount of a defined oxidized derivative of POPC (ALDO-PC) in POPC monolayers before their LB transfer.AFM images of naturally ageing POPC LB films show the appearance of small circular domains after 2 days of exposure to air. These domains (not observed if the samples are kept under vacuum) are characterized by a higher thickness (+0.8 nm) as compared to the intact POPC regions, likely due to a reversal of the oxidized chain which is more polar that intact hydrophobic chains. In the second case, surface pressure measurements show that ALDO-PC induces a slight expansion of the mixed monolayers, suggesting that they are rather homogenous. This hypothesis is confirmed by their smooth and homogenous AFM images. Finally, these results confirm that oxidation in POPC LB films occurs locally in areas presenting likely a looser packing or a defect.

In this paper, we present two types of experimental results. Firstly presented are very good results recently obtained within our group (Nanophysics on soft material and biological systems-CPMOH-Université Bordeaux 1) at the end of a study carried out on octamethylcyclotetrasiloxane (C8H26Si4O3) confined between a plane solid graphite surface and the tip of a commercial Atomic Force Microscope (AFM), used in dynamic mode tapping. Secondly more recent results of a study undertaken on the confinement of salted water, by the same technique, on the mica plane surface are analysed. We show that when the AFM tip approaches the surface, the variation of the amplitude and of the delay of phase of the detected signal, according to the tipsurface distance, present oscillations. The measurement of the period of these oscillations provides a value equal to the diameter of the molecule of the confined liquid. Key words: Confined liquid, AFM probes, tapping-Mode AFM, oscillatory dissipation, effective viscosity.

International audience

International audience; no abstract

International audience; no abstract

International audience; no abstract

International audience; Nanoparticles (NPs) can interact with biological systems, with either negative or positive consequences (potential risks or elimination of pathogenic bacteria). In this context, we investigate the morphology and physico-chemical properties of Escherichia coli bacteria interacting with silica NPs by Atomic Force Microscopy (AFM), this method providing access to topographic information and local rheological properties at the nm scale (with a discrimination between “hard”, NPs, and “soft”, bacteria, materials), either in air or physiological environment. AFM images show that silica NPs tend to aggregate around bacteria, their further action depending on their diameter. The presence of big NPs (100 and 200 nm) does not change E. coli morphology, bacteria remaining rod-shaped and high. The bacterial external membrane keeps also its organization in domains, suggesting that such NPs are too voluminous to penetrate into bacteria. On the contrary, in the presence of small NPs (4 and 10 nm) bacteria adopt unusual spherical shapes, some of them even suffering from a partial collapse, leading to the release of cellular compounds. The external membrane is also disturbed, exhibiting spherical aggregates, which could be due to a reorganization of lipopolysaccharides present in this membrane.