Analytical description of the motion of an acoustic-driven atomic force microscope cantilever in liquid

In this letter the authors present an analytical description that enables determining the motion of an acoustic-driven atomic force microscope cantilever in liquid. The authors show that for low quality factors the effective driving force that acts on the deflection motion depends on the damping. The authors derived equations that accurately give the amplitude and phase of the cantilever deflection and the authors also give the expressions of the damping and stiffness of the interaction

Measurement of the slip length of water flow on graphite surface

We present measurements of the hydrodynamic damping of an atomic force microscopy cantilever-tip immersed in water and approaching a mica surface or a graphite surface. Water completely wets the mica surface while it partially wets the graphite surface with a contact angle of 74°. The measurements show that the damping is higher on mica than on graphite giving a slip length of about 8 nm on this latter surface

Nanomécanique aux interfaces (applications à l'étude de couches de phospholipides et à l'interface air-liquide)

La microscopie à force atomique est utilisée dans de nombreuses applications. Ce travail a ici pour but d'étudier, à l'échelle du nanomètre, les propriétés mécaniques de monocouches et de multicouches de phospholipides avec un microscope à force atomique en mode dynamique. Le comportement non linéaire du système pointe-levier, proche des couches de phospholipides, est étudié avec un modèle de granulation. Le MFA est aussi utilisé pour étudier l'influence d'un peptide membranaire, la syntaxine, et la structure des couches de phospholipides autoassemblées sur du mica. Dans un second temps, nous étudions l'oscillation d'un microlevier de MFA clampé en milieu liquide. Les résultats sont comparés aux prédictions théoriques des simulations numériques de la résolution des équations de Navier-Stokes à trois dimensions, pour mesurer l'influence du mouvement du fluide sur le comportement d'un levier oscillant de MFA. Nous montrons aussi comment la force hydrodynamique peut être réduite d'au moins un ordre de grandeur en usinant, à l'aide d'un faisceau d'ions focalisés (FIB), la largeur du levier. Enfin, nous présentons une description analytique qui détermine le mouvement d'un levier excité acoustiquement en milieu liquide. La troisième partie est une étude du comportement dynamique d'un nanoménisque avec une nanopointe oscillante. La nanoaiguille, découpée avec un faisceau d'ions focalisés, est approchée d'une interface air-liquide et seule son extrémité oscille dans le liquide (Eau-Glycérol-PDMS). Il est montré qu'il est possible d'imager une interface de liquide avec une résolution à l'échelle du nanomètre.Atomic force microscopy (AFM) is used for various applications. This work aims here at studying mechanical properties, at the nanometer scale, of phospholipids monolayers and multilayers with an atomic force microscope in the dynamic mode. The non-linear dynamic behaviour of an oscillating tip-cantilever system, near phopholipids layers, is analyzed based on a coarse graining model. AFM is also applied to study the influence of a membrane peptid, Syntaxyn, and the features of self-assembled phospholipids layers on mica. In a next step, we investigate the oscillation behaviour of a clamped AFM microlever in liquids. The experimental results are compared to theoretical predictions from the numerical solutions of the three-dimensional Navier-Stokes equation, to measure the influence of the fluid motion on the oscillating behaviour of an AFM cantilever. We also show that the drag hydrodynamic force can be reduced by almost an order of magnitude when reducing the cantilever width.using focused ion beam (F.I.B.) milling. Then, we present an analytical description that enables determining the motion of an acoustic-driven atomic force microscope cantilever in liquid. The third part is a study of the dynamical behavior of a nanomeniscus with an oscillating nanoneedle. The nanoneedle, carved with a focus ion beam, is approached to the air-liquid interface and the very end of the tip oscillates in the liquid (Water-Gycerol-PDMS). Shown is the capability to record height images of the liquid interface with resolutions at nanometer scale.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

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Characterization of cadmium accumulation and phytoextraction in three species of the genus Atriplex (canescens, halimus and nummularia) in the presence or absence of salt

International audienceThis study aims to establish for the first time a comparison between the resistance to cadmium (Cd) stress of three halophyte species, Atriplex canescens, Atriplex halimus and Atriplex nummularia in addition to their already known tolerance for salt and drought. Plants were exposed to CdCl2 (20 and 50 μM) in the presence or in the absence of salt (50 mM NaCl) for one and two months. The amount of accumulated Cd was determined in the roots and leaves as well as the amount excreted on the surface of the leaves. Physiological parameters such as chlorophyll content and stress biomarkers, including malondialdehyde and enzymatic activities, were then analyzed. The results show that these plants are able to neutralize the excess of reactive oxygen species resulting from treatments by activating the antioxidant defense mechanisms in order to restore the homeostasis of cells. All three species are also able to accumulate high amounts of Cd in the leaves (several hundred mg of Cd/kg of dry leaves) and this phenomenon is amplified in the presence of salt. All together our results allow to consider the three Atriplex species as hyperaccumulators in the presence/absence of salt and as good candidates in a strategy of Cd phytoextraction in the presence of low concentrations of the pollutant. Nevertheless, both A. canescens and A. nummularia species seem to have a higher capacity to hyper-accumulate Cd when the concentration of Cd reaches higher level of contamination

Oxidation of Langmuir-Blodgett films of monounsaturated lipids studied by atomic force microscopy

In this work, we studied the stability in time of Langmuir-Blodgett films of POPC and OPPC, two unsaturated phospholipids with similar chains, differing by the relative position of these chains on the glycerol backbone. These films, transferred from the air-water interface onto freshly cleaved mica, were characterised by Atomic Force Microscopy (AFM) giving information on their topography at a lateral and perpendicular resolution in the nm range. AFM images (obtained in tapping mode) of freshly transferred films are homogenous, in agreement with the fact that these two lipids are in a liquid-expanded phase under our experimental conditions. After two days, small domains are observed, higher than the surrounding phase of about 0.8 nm in both types of samples. These domains are not observed if the samples are kept under vacuum, or if LB films are made of saturated phospholipids, suggesting that they are due to the local oxidation of POPC or OPPC, the oxidation being slightly more pronounced in the last case. Their dispersion in LB films suggests that oxidation occurs at different points at the same time, likely in areas presenting a loose packing or a defect. The local increase of thickness could be due to the reversal of the oxidised chain, raising the oxidised lipid above the surrounding phase

Dynamic AFM in Liquids: Viscous Damping and Applications to the Study of Confined Liquids

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