Time filter

Source Type

Vuong Q.L.,University of Mons | Berret J.-F.,University Paris Diderot | Fresnais J.,CNRS Analytical Sciences Lab | Gossuin Y.,University of Mons | Sandre O.,CNRS Organic Polymer Chemistry Laboratory
Advanced Healthcare Materials | Year: 2012

Magnetic particles are very efficient magnetic resonance imaging (MRI) contrast agents. In recent years, chemists have unleashed their imagination to design multi-functional nanoprobes for biomedical applications including MRI contrast enhancement. This study is focused on the direct relationship between the size and magnetization of the particles and their nuclear magnetic resonance relaxation properties, which condition their efficiency. Experimental relaxation results with maghemite particles exhibiting a wide range of sizes and magnetizations are compared to previously published data and to wellestablished relaxation theories with a good agreement. This allows deriving the experimental master curve of the transverse relaxivity versus particle size and to predict the MRI contrast efficiency of any type of magnetic nanoparticles. This prediction only requires the knowledge of the size of the particles impermeable to water protons and the saturation magnetization of the corresponding volume. To predict the T2 relaxation efficiency of magnetic single crystals, the crystal size and magnetization - obtained through a single Langevin fit of a magnetization curve - is the only information needed. For contrast agents made of several magnetic cores assembled into various geometries (dilute fractal aggregates, dense spherical clusters, core-shell micelles, hollow vesicles...), one needs to know a third parameter, namely the intra-aggregate volume fraction occupied by the magnetic materials relatively to the whole (hydrodynamic) sphere. Finally a calculation of the maximum achievable relaxation effect - and the size needed to reach this maximum - is performed for different cases: maghemite single crystals and dense clusters, core-shell particles (oxide layer around a metallic core) and zinc-manganese ferrite crystals. © 2012 WILEY-VCH Verlag GmbH & Co.KGaA, Weinheim.

Seth A.,CNRS Analytical Sciences Lab | Bealle G.,CNRS Analytical Sciences Lab | Santanach-Carreras E.,Capsum | Abou-Hassan A.,CNRS Analytical Sciences Lab | Menager C.,CNRS Analytical Sciences Lab
Advanced Materials | Year: 2012

In the core, in the shell, or both: a microfluidic device is used to design magnetic vesicles (liposomes and polymersomes) through chemical modification of the nanoparticle surface. Hydrophilic, hydrophobic and fluorescent quantum dot nanoparticles are used for elaborating the vesicles. Hybrid vesicles are easily obtained with a very high yield and excellent monodispersity. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mignon P.,CNRS Analytical Sciences Lab | Sodupe M.,Autonomous University of Barcelona
Physical Chemistry Chemical Physics | Year: 2012

In the present study, DFT periodic plane wave calculations, at the PBE-D level of theory, were carried out to investigate the interaction of DNA nucleobases with acidic montmorillonite. The surface model was considered in its octahedral (Osub) and tetrahedral (Tsub) substituted forms, known to have different acidic properties. The adsorption of adenine, guanine and cytosine was considered in both orthogonal and coplanar orientations with the surface, interacting with the proton via a given heteroatom. In almost all considered cases, adsorption involved the spontaneous proton transfer to the nucleobase, with a more pronounced character in the Osub structures. The binding energy is about 10 kcal mol -1 larger for Osub than for Tsub complexes mainly due to the larger acidity in Osub surfaces and due to the better stabilization by H-bond contacts between the negatively charged surface and the protonated base. The binding energy of coplanar orientations of the base is observed to be as large as the orthogonal ones due to a balance between electrostatic and dispersion contributions. Finally the binding of guanine and adenine on the acidic surface amounts to 50 kcal mol -1 while that of cytosine rises to 44 kcal mol -1. © 2011 The Owner Societies.

Boichenko A.P.,University of Kharkiv | Berthod A.,CNRS Analytical Sciences Lab
Journal of Chromatography A | Year: 2010

Micellar liquid chromatography (MLC) uses surfactant solutions as mobile phases with added organic additives to enhance both the elution strength and the chromatographic efficiency. Two aliphatic carboxylic acids (1-butanoic and 1-pentanoic) were used as MLC additives and compared with the two corresponding alcohols (1-butanol, 1-pentanol) in terms of elution strength, efficiency and selectivity. A set of 11 phenol derivatives was used as probe compounds. All micellar mobile phases were prepared with sodium dodecylsulfate (SDS) with concentration ranging from 0.05 to 0.15. M and the modifier content within 1.0 and 5.0% (v/v). The elution strength of different mobile phases containing a constant amount of SDS and different amounts of modifiers; and mobile phases containing a constant amount of modifier and different SDS concentration were determined and discussed. The effect of the acid modifiers on efficiency was studied constructing van Deemter plots that showed no minimum within the 0.01-0.7. mL/min flow rate range studied. Temperature effects were also studied constructing the classical van't Hoff plots. The slight curvature of the plots in the 25-70°C range may indicate some modification of the surfactant-bonded moiety layer on the stationary phase surface. Since no definitive advantage of the use of aliphatic acids were established compared to their alcohol counterpart, their terrible smell will probably preclude their use as MLC organic modifiers. © 2010 Elsevier B.V.

Lagarde F.,CNRS Analytical Sciences Lab | Jaffrezic-Renault N.,CNRS Analytical Sciences Lab
Analytical and Bioanalytical Chemistry | Year: 2011

During recent decades, extensive industrialisation and farming associated with improper waste management policies have led to the release of a wide range of toxic compounds into aquatic ecosystems, causing a rapid decrease of world freshwater resources and thus requiring urgent implementation of suitable legislation to define water remediation and protection strategies. In Europe, the Water Framework Directive aims to restore good qualitative and quantitative status to all water bodies by 2015. To achieve that, extensive monitoring programmes will be required, calling for rapid, reliable and cost-effective analytical methods for monitoring and toxicological impact assessment of water pollutants. In this context, whole cell biosensors appear as excellent alternatives to or techniques complementary to conventional chemical methods. Cells are easy to cultivate and manipulate, host many enzymes able to catalyse a wide range of biological reactions and can be coupled to various types of transducers. In addition, they are able to provide information about the bioavailability and the toxicity of the pollutants towards eukaryotic or prokaryotic cells. In this article, we present an overview of the use of whole cells, mainly bacteria, yeasts and algae, as sensing elements in electrochemical biosensors with respect to their practical applications in water quality monitoring, with particular emphasis on new trends and future perspectives. In contrast to optical detection, electrochemical transduction is not sensitive to light, can be used for analysis of turbid samples and does not require labelling. In some cases, it is also possible to achieve higher selectivities, even without cell modification, by operating at specific potentials where interferences are limited. © 2011 Springer-Verlag.

Hassan N.,CNRS Analytical Sciences Lab | Cabuil V.,CNRS Analytical Sciences Lab | Abou-Hassan A.,CNRS Analytical Sciences Lab
Angewandte Chemie - International Edition | Year: 2013

Lab-on-a-particle: Fluorescent, plasmonic, and magnetic SiO 2-Au-γ-Fe2O3 nanostructures were assembled under continuous flow using two microfluidic devices (μR1 and μR2) connected in series. After assembling the SiO2-Au nanostructures by electrostatic interactions, γ-Fe2O 3 nanoparticles were attached to the structures (see picture). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mekaoui N.,CNRS Analytical Sciences Lab | Berthod A.,CNRS Analytical Sciences Lab
Journal of Chromatography A | Year: 2011

Countercurrent chromatography (CCC) is a separation technique using a biphasic liquid system and centrifugal forces to maintain a support-free liquid stationary phase. Either one of the two phases can be the liquid stationary phase. It is even possible to switch the phase role during the separation. The dual-mode method is revisited recalling its theoretical background. The multi-dual mode (MDM) CCC method was introduced to enhance the resolution power of a CCC column. The theoretical study of the MDM method is validated by modeling the separation of two solutes. The basic hypothesis is that the forward step (partial classical elution) is followed by a backward step that returns the less retained solute to the column head. The equations show that the most important parameter to maximize resolution is not the number of MDM steps but the total volume of liquid phases used to elute the solutes. The model is validated calculating correctly the peak position of previously published MDM experiments. © 2011 Elsevier B.V.

Berthod A.,CNRS Analytical Sciences Lab | Mekaoui N.,CNRS Analytical Sciences Lab
Journal of Chromatography A | Year: 2011

There is some confusion in chromatography between terms such as solute distribution ratio, distribution constant and partition coefficient. These terms are very precisely defined in the field of liquid-liquid systems and liquid-liquid extraction as well as in the field of chromatography with sometimes conflicting definitions. Countercurrent chromatography (CCC) is a chromatographic technique in which the stationary phase is a support-free liquid. Since the mobile phase is also liquid, biphasic liquid systems are used. This work focuses on the exact meaning of the terms since there are consequences on experimental results. The retention volumes of solutes in CCC are linearly related to their distribution ratios. The partition coefficient that should be termed (IUPAC recommendation) distribution constant is linked to a single definite species. Using benzoic acid that can dimerize in heptane and ionize in aqueous phase and an 18. mL hydrodynamic CCC column, the role and relationships between parameters and the consequences on experimental peak position and shape are discussed. If the heptane/water distribution constant (marginally accepted to be called partition coefficient) of benzoic acid is 0.2 at 20 °C and can be tabulated in books, its CCC measured distribution ratio or distribution coefficient can change between zero (basic aqueous mobile phase) and more than 25 (acidic aqueous mobile phase and elevated concentration). Benzoic acid distribution ratio and partition coefficient coincide only when both dimerization and ionization are quenched, i.e. at very low concentration and pH 2. It is possible to quench dimerization adding butanol in the heptane/water system. However, butanol additions also affect the partition coefficient of benzoic acid greatly by increasing it. © 2010 Elsevier B.V.

Thiebaut D.,CNRS Analytical Sciences Lab
Journal of Chromatography A | Year: 2012

This paper gives a survey of the most attractive trends and applications of supercritical fluid chromatography in the petroleum industry: simulated distillation, group-type analysis and related applications including the implementation of multidetection in a so-called " hypernated" system, as well as the hyphenation to GC×GC for improved group-type separation, SFC×GC and first promising SFC×SFC results. Some specific technical information related to the use of capillary columns or conventional packed columns in combination with FID (or detectors that require decompression and in some instances splitting of the mobile phase prior detection) is also provided. © 2012 Elsevier B.V.

Heinisch S.,CNRS Analytical Sciences Lab | D'Attoma A.,CNRS Analytical Sciences Lab | Grivel C.,CNRS Analytical Sciences Lab
Journal of Chromatography A | Year: 2012

The performance characteristics of separation were studied for small pharmaceuticals and larger charged molecules (peptides) in various mobile phase conditions on two 5-cm long narrow bore columns packed with 1.7 μm core-shell and totally porous particles respectively. The effect of temperature and pH additives (formic acid, trifluoroacetic acid, ammonium formate, ammonium acetate and ammonia) on column efficiency was investigated through a kinetic study based upon data obtained under gradient elution conditions. Sample peak capacities were calculated and compared in all studied conditions for a sample of ten representative peptides having masses ranging from 500 to 2000. Da. The elevation of temperature was found to be significantly beneficial. The effect of flow-rate on peak shape was also investigated. Ammonium acetate at neutral pH led to the best results in terms of both efficiency and peak capacity. It was found that column performance was strongly dependent on the type of stationary phase, especially in acidic medium. © 2011 Elsevier B.V.

Loading CNRS Analytical Sciences Lab collaborators
Loading CNRS Analytical Sciences Lab collaborators