Conformational Structural Changes of Bacteriorhodopsin Adsorbed onto Single-Walled Carbon Nanotubes

International audienceThe interaction between purple membranes, composed of proteins of bacteriorhodopsin (bR) and their native Surrounding lipids, and single-walled carbon nanotubes (SWNT) has been investigated. In this work, sonication has been used to debundle SWNT in buffer solution without surfactant before the addition of native purple membranes. The sample was then sonicated in a bath for a short time, followed by a centrifugation. The supernatants contain proteins in excess and SWNT as individual and small bundles covered by a bR layer with an average thickness of 1.5 nm. TEM and AFM observations support the idea that only a protein monolayer surrounds the tubes. Optical absorption and infrared spectroscopy measurements provide evidence that the proteins adsorbed onto the SWNT undergo orientational changes of the helical segments in bR and helix conformational changes. We ascribe the main driving force to the hydrophobic interactions between the sidewall of the SWNT and the hydrophobic residues of the alpha-helices of bR

Complexes nanotubes de carbone monoparois / polysaccharides (caractérisation de l'association et mécanisme)

Aujourd hui, les études sur les nanotubes de carbone (NTC) et plus particulièrement sur leur utilisation dans le domaine du biomédical sont en plein développement. Nos travaux s inscrivent dans cette dynamique et sont consacrés à la formation et à la caractérisation de complexes NTC monoparois / Polysaccharides, en vue de la réalisation, à long terme, de biocapteurs à transduction optique. Les polysaccharides utilisés sont des dérivés d amylose et de cellulose. L objectif est de comprendre les interactions entre ces biopolymères et les NTC, qui permettent la dispersion et l individualisation des NTC en milieu aqueux. Pour ce faire, les complexes sont formés en solution aqueuse en présence d ultra-sons, isolés par centrifugation et étudiés notamment par spectroscopie d absorption optique, de diffusion Raman et d émission et microscopie à force atomique. L efficacité et le rendement de la dispersion est fonction d un polysaccharide donné. C est avec la carboxyméthylcellulose que les dispersions obtenues sont les plus performantes. Par variation de la conformation du biopolymère, de son état de charge, de son hydrophobicité, du milieu réactionnel (solvant, pH, salinité) nous avons pu montrer que l interaction dominante mise en jeu est de type CH-p entre le NTC et le groupement glucosidique de la chaîne principale. Une conformation étendue du biopolymère favorise cette association. Les interactions hydrophobes et électrostatiques interviennent aussi dans le mécanisme d association et induisent une légère sélectivité envers les NTC semi conducteurs. Bien que nous n ayons pas encore pu réaliser de biocapteurs, les complexes obtenus répondent aux critères permettant de le faire.This thesis tackles the fields of carbon nanotubes and their biomedical applications. In that purpose, Single-Walled Carbon Nanotubes (SWNT) / Polysaccharides complexes are prepared in water by an ultrasound process and isolated by a centrifugation step and then characterized. The long term application of such systems could be the fabrication of a biosensor with optical detection.Different kinds of cellulose and amylose derivatives are used in order to individualize SWNT in water in a stable way. We show that the polysaccharide water solubility, its conformation in solution and its structure are as much different parameters which have to be taken into account for the determination of the effectiveness and the yield of the dispersion. To understand the mechanism of interaction between polysaccharide and SWNT, we use in particular optical absorption, Raman and emission spectroscopy and atomic force microscopy. Effectiveness and yield are function of a given polysaccharide. Carboxymethylcellulose is shown as one of the best dispersant for SWNT. Excellent individualization of the SWNT is observed. Modification of the polymer charge, of its hydrophobicity or of the reaction medium (salt, pH, solvent) prove that a flat conformation of the biopolymer favours the interaction. In this study, we have shown that the main mechanism of interaction may consist in a CH-p interaction between the glucose chain of the polysaccharide and the sidewall of the carbon nanotubes. Electrostatic and hydrophobic forces also have to be considered in the association mechanism and induce a weak selectivity of the process for semiconductor nanotubes. The complexes may be used for building biosensors.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Morphology of DNA/single walled nanotubes complexes

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Cellulosic nanorods of various aspect ratios for oil in water Pickering emulsions

International audienceCellulosic colloidal nanorods of different origins were used in order to investigate the effect of various elongated shapes adsorbed at the oil-water interface for Pickering emulsion characteristics. Nanocrystals of length ranging from 185 nm to 4 μm were obtained from the hydrolysis of cellulose microfibrils of three different biological origins: cotton (CCN), bacterial cellulose (BCN) and Cladophora (ClaCN) leading to aspect ratios ranging from 13 to 160. These nanocrystals are irreversibly adsorbed at the oil-water interface and form ultrastable emulsions. Individual droplets of similar diameter were obtained under diluted conditions, illustrating both similar wetting properties and nanocrystal flexibility for the three different types of nanocrystals. However, it was shown that the aspect ratio directly influences the coverage ratio giving rise, on the one hand to a dense organisation (coverage >80%) with short nanocrystals and on the other hand to an interconnected network of low covered droplets (40%) when longer nanocrystals are used. An estimation is made showing that for the longer nanocrystals, 55% of the nanocrystals introduced are involved in the network of the material. The capillary force that promotes attractive interactions between nanocrystals was also addressed. These results lead to a better understanding of the adsorption process for rod-like particles of various aspect ratios for the elaboration of a controlled surface architecture, from a homogeneous monolayer to interconnected porous multilayered interfaces

Macroporous hybrid Pickering foams based on carbon nanotubes and cellulose nanocrystals

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Early adhesion of human mesenchymal stem cells on TiO2 surfaces studied by single-cell force spectroscopy measurements

International audienceUnderstanding the interactions involved in the adhesion of living cells on surfaces is essential in the field of tissue engineering and biomaterials. In this study, we investigate the early adhesion of living human mesenchymal stem cells (hMSCs) on flat titanium dioxide (TiO2) and on nanoporous crystallized TiO2 surfaces with the use of atomic force microscopy-based single-cell force spectroscopy measurements. The choice of the substrate surfaces was motivated by the fact that implants widely used in orthopaedic and dental surgery are made in Ti and its alloys. Nanoporous TiO2 surfaces were produced by anodization of Ti surfaces. In a typical force spectroscopy experiment, one living hMSC, immobilized onto a fibronectine-functionalized tipless lever is brought in contact with the surface of interest for 30 s before being detached while recording force-distance curves. Adhesion of hMSCs on nanoporous TiO2 substrates having inner pore diameter of 45 nm was lower by approximately 25% than on TiO2 flat surfaces. Force-distance curves exhibited also force steps that can be related to the pulling of membrane tethers from the cell membrane. The mean force step was equal to 35 pN for a given speed independently of the substrate surface probed. The number of tethers observed was substrate dependent. Our results suggest that the strength of the initial adhesion between hMSCs and flat or nanoporous TiO2 surfaces is driven by the adsorption of proteins deposited from serum in the culture media

Relationship between Young's Modulus and Film Architecture in Cellulose Nanofibril-Based Multilayered Thin Films

Young's moduli of cellulose nanofibril (CNF)-poly(allylamine hydrochloride) (PAH) multilayered thin films were measured using strain-induced elastic buckling instability for mechanical measurements (SIEBIMM) and the quantitative nanomechanical mapping technique (PF-QNM). To establish the relationship between structure and mechanical properties, three types of films with various architectures were built using the layer-by-layer method by changing the ionic strength of the dipping solution. Both methods demonstrate that the architecture of a film has a strong impact on its mechanical properties even though the film has similar cellulose content, emphasizing the role of the architecture. Films with lower porosity (Phi(air) = 0.34) and a network display the highest Young's moduli (9.3 GPa), whereas others with higher and similar porosity (Phi(air) = 0.46-0.48) present lower Young's moduli (4.0-5.0 GPa). PF-QNM measurements indicate a reverse ranking that is probably indicative of the surface composition of the films

Highly Efficient and Predictable Noncovalent Dispersion of Single-Walled and Multi-Walled Carbon Nanotubes by Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are shown to be able to disperse in a very efficient way both single-walled (SWNTs) and multiwalled carbon nanotubes (MWNTs). Optimization of the processing parameters (sonication time and power) leads to dispersion yields as high as 70 wt % for both types of carbon nanotubes (CNTs). Such a high dispersion yield obtained in a noncovalent way with biobased nanoparticles is noteworthy and deserves further attention. Atomic force microscopy and transmission electron microscopy images suggest that the CNCs and the nanotubes form hybrids, with the stabilization of the dispersion arising from both the irreversible adsorption of the CNCs onto the nanotubes and the electrostatic repulsion between the CNCs. A quantitative model is proposed, revealing that one CNC can stabilize one SWNT three times its length in the aqueous dispersion and that more CNCs are required in the case of MWNTs. This model allows us to control the dispersion yield as a function of the processing parameters

Temperature dependence of unbinding forces between complementary DNA strands.

Force probe techniques such as atomic force microscopy can directly measure the force required to rupture single biological ligand receptor bonds. Such forces are related to the energy landscape of these weak, noncovalent biological interactions. We report unbinding force measurements between complementary strands of DNA as a function of temperature. Our measurements emphasize the entropic contributions to the energy landscape of the bond

Carbon Nanotube/Cellulose Nanocrystal Hybrid Conducting Thin Films

Cellulose nanocrystals (CNCs) have a high ability to disperse single-walled carbon nanotubes (SWNTs) in aqueous media and to form hybrids. These hybrids are used to grow layer-by-layer thin films of controlled thickness. Thanks to the presence of SWNTs, these films are conducting. In this article, we describe the process by which the CNC/SWNT hybrids are obtained and discuss the electrical properties of the hybrid-based layer-by-layer films