Small Bioactivated Magnetic Quantum Dot Micelles

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Dynamic force spectroscopy to probe adhesion strength of living cells

We studied the mechanical strength of the adhesion of living cells to model membranes. The latter contained a RGD lipopeptide which is a high affinity binding site for a cell adhesion molecule (integrin alpha(V)beta(3)). Cells adhered specifically to the vesicles. We used micropipette aspiration for breaking this adhesion with well defined forces. Systematic variation of the rate of force application revealed pronounced kinetic effects. The dependence of the detachment forces on the loading rate was well described by a power law (exponent approximate to0.4), in agreement with recent theoretical work

Adhesion of Arg-Gly-Asp (RGD) peptide vesicles onto an integrin surface : visualization of the segregation of RGD ligands into the adhesion plaques by fluorescence

Integrins are adhesion receptors that mediate cell adhesion and play an important function in many biological processes such as morphogenesis and tissue remodeling. These membrane proteins specifically interact with a short tripeptide sequence, RGD (Arg-Gly-Asp), present in numerous extracellular macromolecules. Model systems have been developed in order to understand how membrane adhesion is induced by this specific RGD peptide ligand/integrin recognition system. We have previously shown that RGD giant vesicles selectively adhere to endothelial cells by formation of pinning centers. Nevertheless, the nature of the lipids located in the adhesion contact zone is unknown. One hypothesis is that the lipidic ligands migrate to the contact zone where they are confined after binding to the receptor. To study the possible formation of ligand domains within the vesicle bilayer, we synthesized a fluorescently labeled RGD lipid that can be easily incorporated in giant vesicles. Adhesion of giant RGD vesicles onto an integrin-functionalized surface was followed simultaneously by reflection interference contrast microscopy and fluorescence microscopy. For the first time, it was possible to observe the microsegregation of RGD lipids in the contact zone during adhesion. Additionally, we observed interesting photosensitive properties of the chalcone chromophore that could lead to a new method of analyzing the lipid organization within the membrane during adhesion and to the design of new ligand lipids and vesicle vectors for cell targeting

Water-soluble pegylated quantum dots: from a composite hexagonal phase to isolated micelles

International audienceWe present a simple method based on the dispersion of fluorescent quantum dots (QD) into a liquid crystal phase that provides either nanostructured material or isolated QD micelles depending on water concentration. The liquid-crystal phase was obtained by using a gallate amphiphile with a poly(ethylene glycol) chain as the polar headgroup, named I. The hydration of QD/I mixtures resulted in the formation of a composite hexagonal phase identified by small-angle X-ray scattering and by polarized light and fluorescence optical microscopy, showing a homogeneous distribution of fluorescence within hexagonal phase. This composite mesophase can be converted into isolated QD-I micelles by dilution in water. The fluorescent QD-I micelles, purified by size exclusion chromatography, are well monodisperse with a hydrodynamic diameter of 20-30 nm. Moreover, these QD do not show any nonspecific adsorption on lipid or cell membranes. By simply adjusting the water content, the PEG gallate amphiphile I provides a simple method to prepare a self-organized composite phase or pegylated water soluble QD micelles for biological applications

Control of the interaction between membranes or vesicles : adhesion, fusion and release of dyes

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Replacement of CTAB with peptidic ligands at the surface of gold nanorods and their self-assembling properties

International audienceHerein, we describe the self-assembling of gold nanorods (GNRs) induced during the ligand exchange at their surface. An exchange reaction between tricysteine PEGylated peptidic ligands and cetyltrimethylammonium bromide (CTAB)-protected gold nanorods is conducted. We demonstrated that the terminal group charge (positively or negatively charged) and the hydrophobicity of the peptidic ligands (bearing or not an undecanoyl chain) strongly affects the self-organization of the GNRs occurring in solution. Adjusting the amount of short PEGylated peptides causes a self-organization of the gold nanorods in solution, resulting in a red- or blue-shift of the plasmon bands. The decrease of their surface charge and the self-assembling in solution were first shown by zetametry, by Dynamic Light Scattering and UV-spectroscopy. Thanks to Small Angle X-ray Scattering experiments and Transmission Electron Microscopy images, the self-organization of the nanorods in solution was clearly demonstrated and correlated to the spectroscopic change in absorbance. Conversely, in the case of longer PEGylated peptidic ligands including an undecanoyl chain, the GNRs are particularly stable against aggregation for several days after purification. By controlled drying on a substrate, we showed their ability to self-organize into well-defined ordered structures making them very attractive as building blocks to design optical materials. (C) 2014 Elsevier Inc. All rights reserved