Optimized network of multi-walled carbon nanotubes for chemical sensing.

This work reports the design of a resistive gas sensor based on 2D mats of multi-walled carbon nanotubes (MWCNTs) grown by aerosol-assisted chemical vapour deposition. The sensor sensitivity was optimized using chlorine as analyte by tuning both CNT network morphology and CNT electronic properties. Optimized devices, operating at room temperature, have been calibrated over a large range of concentration and are shown to be sensitive down to 27 ppb of chlorine. The as-grown MWCNT response is compared with responses of 2000 °C annealed CNTs, as well as of nitrogen-doped CNTs and CNTs functionalized with polyethyleneimine (PEI). Under chlorine exposure, the resistance decrease of as-grown and annealed CNTs is attributed to charge transfer from chlorine to CNTs and demonstrates their p-type semiconductor behaviour. XPS analysis of CNTs exposed to chlorine shows the presence of chloride species that confirms electron charge transfer from chlorine to CNTs. By contrast, the resistance of nitrogen-doped and PEI functionalized CNTs exposed to chlorine increases, in agreement with their n-type semiconductor nature. The best response is obtained using annealed CNTs and is attributed to their higher degree of crystallinity.

Aligned carbon nanotube based ultrasonic microtransducers for durability monitoring in civil engineering.

Structural health monitoring of porous materials such as concrete is becoming a major component in our resource-limited economy, as it conditions durable exploitation of existing facilities. Durability in porous materials depends on nanoscale features which need to be monitored in situ with nanometric resolution. To address this problem, we put forward an approach based on the development of a new nanosensor, namely a capacitive micrometric ultrasonic transducer whose vibrating membrane is made of aligned single-walled carbon nanotubes (SWNT). Such sensors are meant to be embedded in large numbers within a porous material in order to provide information on its durability by monitoring in situ neighboring individual micropores. In the present paper, we report on the feasibility of the key building block of the proposed sensor: we have fabricated well-aligned, ultra-thin, dense SWNT membranes that show above-nanometer amplitudes of vibration over a large range of frequencies spanning from 100 kHz to 5 MHz.

RGD-functionalized spherulites as targeted vectors captured by adherent cultured cells.

Spherulites are multilamellar vesicles consisting of concentric shells that can encapsulate small organic molecules or macromolecules. We investigate the possibility of targeting neutral spherulites to adherent culture cells by functionalizing their surface with RGD-containing ligands. The strength and specificity of association of RGD spherulites with several cell lines (EAhy 926 endothelial cell line, human umbilical vein endothelial cell (HUVEC) and human osteoprogenitor (HOP) primary cells) was studied, and the molecular interaction of RGD spherulites with the EAhy 926 cell surface was investigated. We show that, after binding to cells, spherulites are internalized.

A noble metal-free proton-exchange membrane fuel cell based on bio-inspired molecular catalysts.

Hydrogen is a promising energy vector for storing renewable energies: obtained from water-splitting, in electrolysers or photoelectrochemical cells, it can be turned back to electricity on demand in fuel cells (FCs). Proton exchange membrane (PEM) devices with low internal resistance, high compactness and stability are an attractive technology optimized over decades, affording fast start-up times and low operating temperatures. However, they rely on the powerful catalytic properties of noble metals such as platinum, while lower cost, more abundant materials would be needed for economic viability. Replacing these noble metals at both electrodes has long proven to be a difficult task, so far incompatible with PEM technologies. Here we take advantage of newly developed bio-inspired molecular H2 oxidation catalysts and noble metal-free O2-reducing materials, to fabricate a noble metal-free PEMFC, with an 0.74 V open circuit voltage and a 23 µW cm-2 output power under technologically relevant conditions. X-ray absorption spectroscopy measurements confirm that the catalysts are stable and retain their structure during turnover.

Conception and realization of a non-cationic non-viral DNA vector.

Cationic non-viral DNA vectors are very successful in in vitro transfections but less efficient in in vivo tests. This seems mainly due to the cationic nature of the molecules used to complex DNA. In this article, we describe the design and the route towards the realization of a non-viral non-cationic vector. The strategy follows three steps: first, the incorporation of DNA to a lamellar phase; second, the making of multilamellar vesicles containing a high loading of DNA by shearing the lamellar phase and, finally, the grafting of peptides onto the surface of the vesicles to target a specific receptor on the cells. Throughout this process, we had to overcome many obstacles; this review describes the present state of our work and summarizes the remaining steps.

Chicken embryonic stem cells and transgenic strategies.

The production of transgenic birds is an important goal for both fundamental and applied biology. Different methods have been employed to generate transgenic chickens, including microinjection, use of retroviruses and transfection of primordial germ or embryonic germ cells. In this review we will briefly describe these techniques and our efforts to obtain genetically modified avian embryonic stem (ES) cells using liposomes. This latter technique should allow us to modify chicken ES cells with a high efficiency, permitting the rapid generation of transgenic bird lines.

Chemical characterization of alpha-oxohydrazone ligation on colloids: toward grafting molecular addresses onto biological vectors.

New mild and specific chemical strategies have been developed recently for the selective coupling of biological macromolecules. Among them, the hydrazone ligation strategy offers high chemoselectivity and versatility. We intended to use hydrazone ligation to target the controlled release of therapeutic agents by biological vectors (multilamellar vesicles called onion vectors). An accurate measure of ligation bond stability was needed to ensure that the ligation bond would stand long exposures to physiological conditions. In this study, we have completed a kinetic and thermodynamic characterization of hydrazone formation on a model reaction. The mechanism of the reaction in solution as well as in different self-organized systems (micelles, liposomes and multilamellar vesicles) was investigated. In solution, submicromolar stability was achieved as well as half-lives of several weeks. The kinetics and stability were both enhanced in colloidal media thanks to autoassociation effects. The results were expanded to the realistic case of RGD-peptide coupling to onion vectors. The RGD grafted onion vectors were then tested for their ability to bind endothelial cells in vitro.

Interaction of cationic colloids at the surface of J774 cells: a kinetic analysis.

We have characterized the binding of multilamellar colloids to J774 cells. Cationic colloids were shown to bind much more efficiently than neutral ones. Particle uptake by cells was followed by flow cytometry and fluorescence microscopy. Analysis of the kinetics of uptake of cationic particles indicated that binding on the cell surface occurred with two characteristic times. Analysis of the dissociation properties allowed discriminating between several alternative models for adsorption and led us to propose a mechanism that involved two independent classes of binding sites on the cell surface. One class of sites appeared to be governed by a classic mass action law describing a binding equilibrium. The other sites were populated irreversibly by particles made of 10% cationic lipids. This was observed in the absence of endocytosis, under conditions where both the equilibrium and the irreversible binding occurred at the cell surface. We determined the rate constants for the different steps. We found that the reversible association occurred with a characteristic time of the order of tens of seconds, whereas the irreversible binding took a hundred times longer. The presence of serum proteins in the incubation medium did not drastically affect the final uptake of the particles. In contrast, the capture of the particles by cells significantly dropped when the fraction of positively charged lipids contained in the colloids was decreased from 10% to 5%. Finally, the results will be discussed within a comprehensive model where cationic particles find labile binding sites in the volume of the pericellular network (glycocalyx and extracellular matrix) and less-accessible irreversible binding sites at the cell membrane itself.

Determination of ethambutol in plasma by high-performance liquid chromatography after pre-column derivatization.

A new HPLC assay using UV detection (200 nm) was developed to determine ethambutol (EMB) concentrations in plasma. Following extraction (0.1 ml plasma) with chloroform, EMB and octylamine (used as internal standard) were derivatized with phenylethylisocyanate. Quantitation in plasma was achieved at 200 nm. There were no interferences from endogenous compounds. Intra- and inter-day variabilities were lower than 5.2 and 7.6%, respectively. The limit of quantitation of the method was 0.2 microg/ml. In plasma, ethambutol was found to be stable for at least one month when samples were stored at -20 degrees C. This assay was applied to the therapeutic monitoring of EMB concentrations in 19 patients suffering from tuberculosis.