Search

International audience; Surface plasmon resonance (SPR) is a powerful technique for label-free and real-time characterization of molecular interactions at interfaces. However, the detection of small molecules still remains a challenge. Here, we report on the direct detection of a low-molecular-weight compound by its receptor presented as a monolayer. Moreover, the signal observed is more than twice the expected mass-weighted response. To establish the origin of the signal enhancement, we present herein a theoretical model that simulates the maximal SPR response by taking into account the aptamer conformational change. We demonstrated that the variation of layer thickness is not the only parameter to be considered. We highlighted that the conformational transition of the aptamer also induces a deviation of the refractive index increment (RII) of the target/aptamer complex from the sum of the RII of individual entities. This nonadditivity of the RII significantly contributes to the magnitude of the signal. We also propose the prediction of the maximal SPR response as a function of the penetration depth, the ratio of the mass-weighted RII of the partners, the sensing layer thickness, and the correction of the complex RII. This model provides new insights into parameters to be considered for the analysis of SPR signals.

This work describes how nanostructured thin films obtained from the self-assembly of block copolymers (BCPs) systems can be used as a nanoelectrode array (NEA) that can be programmed to specifically detect targeted molecules. Namely, poly(styrene-b-methacrylate) (PS-b-PMMA) thin films, after removal of PMMA phase, produced regular spaced 560 pores μm-2 with 16 nm of diameter. The nanopores were then chemically modified by the introduction of β-cyclodextrin (β-CD) molecules. By using the supramolecular interaction of β-CD and ferrocene (Fc), the pores could be programed by the introduction of molecules linked to Fc able to interact with target species. In the model system shown here, the linker had a biotin unit, aiming the detection of streptavidin. By changing the linker, other molecules can also be detected. This concept opens a window to many possibilities, including the development of devices for fast and versatile molecule detection.

Immobilized proteins or peptides are of critical importance for applications such as biosensing or cell culture. We analyze the structure of layers of a large variety of proteins and peptides, grafted on silicon substrates by different routes differing in the nature of the intermediate layer linking the biomolecules to the substrate, either a silane monolayer, or a polyelectrolyte multilayer made from synthetic or natural polymers. The structural analysis is essentially performed by X-ray reflectometry, which proves to be an efficient methodology not requiring the use of tagged biomolecules, capable of evaluating consistently the amount of grafted biomolecules per surface area with estimated precisions ranging from 10 to 20%. The study provides a quantitative basis for selecting one among a series of well-proofed and sturdy grafting methodologies and underlines the potential of XRR for assessing the amount of grafted biomacromolecules without requiring the expensive tagging of molecules. Our results also show that, for the coupling route resting on synthetic polyelectrolytes, the grafting density is significantly lower than for direct coupling over a silane layer. In contrast, when performed over a cushion based on polysaccharides, the grafting density is well above the values found for a dense layer grafted on a silane monolayer, indicating partial penetration and swelling of the polysaccharide cushion.

Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) was used to investigate the mucoadhesive properties of nanoparticles decorated with low, medium and high molar mass chitosan (CS). Uncoated and chitosan-coated polycaprolactone (PCL) nanoparticles loaded with curcumin were prepared by nanoprecipitation method and characterized in terms of size, surface charge and drug content. The interactions between nanoparticles and mucin layer were monitored after the treatment of SAM-functionalized gold-coated quartz crystals with bovine submaxillary gland mucin (BSM). The results show that all investigated chitosan-coated nanoparticles adsorb onto the BSM layer, and the mass uptake was found to be independent of the chitosan molar mass. Uncoated nanoparticles showed, however, no affinity with BSM layer, confirming that the adsorption of colloidal systems occurs due to their decoration with chitosan. The adhesion is mainly attributed to electrostatic interactions between protonated amino groups of mucoadhesive chitosan and negatively charged groups of mucin. The results suggest that chitosan-coated nanoparticles are promising carriers for hydrophobic drugs delivery in the buccal mucosa.

Multilayer films made of poly(diallyldimethylammonium) (PDDA), gold nanoparticles (AuNP) of 10 nm diameter and lactate oxidase (LOx), were built for the first time, by layer-by-layer (LBL) assembly technique onto both quartz and gold substrates. The surface plasmon resonance (SPR) band of AuNP was used for monitoring the film growth and adsorption kinetics on PDDA monolayer supported onto quartz substrate. In the case of polycrystalline gold surfaces, electrochemical characterization was performed by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The latter system was used as bioelectrode for L-lactate quantification, showing a short time response (

On procede a une revue critique des methodes d'ingenierie utilisees dans le processus de conception des centrales nucleaires en examinant les aspects geotechniques et structurels. Le cas de la centrale de Cruas, construite sur isolation sismique, est presente dans les grandes lignes. On decrit ensuite les methodes disponibles en situation de reevaluation sismique, avant de terminer par les perspectives d'evolution de la pratique d'ingenierie et les actions de R&D d'accompagnement.

A biosensor based on the immobilization of Lactate oxidase in laponite–organosilasesquioxane films on glassy carbon electrode for the quantification of L-lactate in wine and dairy products is presented. The bioelectrode showed a very high sensitivity (0.33±0.01) A cm−2 M−1 and a short time response (10 s) for less than 1 U of enzyme. No significant interferences, including ascorbic acid, were detected. For red wine, matrix effects assigned to polyphenols and anthocyanins were observed, which ware easily overcome by sample dilution. Our L-lactate determinations were in good agreement with those of two standard methods.

Deoxyuridine 5'-triphosphate pyrophosphatases (dUTPases) are ubiquitous enzymes essential for hydrolysis of dUTP, thus preventing its incorporation into DNA. Although Epstein-Barr virus (EBV) dUTPase is monomeric, it has a high degree of similarity with the more frequent trimeric form of the enzyme. In both cases, the active site is composed of five conserved sequence motifs. Structural and functional studies of mutants based on the structure of EBV dUTPase gave new insight into the mechanism of the enzyme. A first mutant allowed us to exclude a role in enzymatic activity for the disulfide bridge involving the beginning of the disordered C terminus. Sequence alignments revealed two groups of dUTPases, based on the position in sequence of a conserved aspartic acid residue close to the active site. Single mutants of this residue in EBV dUTPase showed a highly impaired catalytic activity, which could be partially restored by a second mutation, making EBV dUTPase more similar to the second group of enzymes. Deletion of the flexible C-terminal tail carrying motif V resulted in a protein completely devoid of enzymatic activity, crystallizing with unhydrolyzed Mg(2+)-dUTP complex in the active site. Point mutations inside motif V highlighted the essential role of lid residue Phe(273). Magnesium appears to play a role mainly in substrate binding, since in absence of Mg(2+), the K(m) of the enzyme is reduced, whereas the k(cat) is less affected.

Biologically programmed molecular recognition provides the basis of all natural systems and supplies evolution-optimized functional materials from self-assembly of a limited number of molecular building blocks. Biomolecules such as peptides, nucleic acids and carbohydrates represent a diverse supply of structural building blocks for the chemist to design and fabricate new functional nanostructured architectures. In this context, we review here the chemistry we have developed to conjugate peptides with nucleic acids, carbohydrates, and organic molecules, as well as combinations thereof using a template-assembled approach. With this methodology, we have prepared new integrated functional systems exhibiting designed properties in the field of nanovectors, biosensors as well as controlled peptide self-assembly. Thus this molecular engineering approach allows for the rational design of systems with integrated tailor-made properties and paves the way to more elaborate applications by bottom-up design in the domain of nanobiosciences.

Aptamers have emerged as promising biorecognition elements in the development of biosensors. The present work focuses on the application of quartz crystal microbalance with dissipation monitoring (QCM-D) for the enantioselective detection of a low molecular weight target molecule (less than 200 Da) by aptamer-based sensors. While QCM-D is a powerful technique for label-free, real-time characterization and quantification of molecular interactions at interfaces, the detection of small molecules interacting with immobilized receptors still remains a challenge. In the present study, we take advantage of the aptamer conformational changes upon the target binding that induces displacement of water acoustically coupled to the sensing layer. As a consequence, this phenomenon leads to a significant enhancement of the detection signal. The methodology is exemplified with the enantioselective recognition of a low molecular weight model compound, L-tyrosinamide (L-Tym). QCM-D monitoring of L-Tym interaction with the aptamer monolayer leads to an appreciable signal that can be further exploited for analytical purposes or thermodynamics studies. Furthermore, in situ combination of QCM-D with spectroscopic ellipsometry unambiguously demonstrates that the conformational change induces a nanometric decrease of the aptamer monolayer thickness. Since QCM-D is sensitive to the whole mass of the sensing layer including water that is acoustically coupled, a decrease in thickness of the highly hydrated aptamer layer induces a sizable release of water that can be easily detected by QCM-D.

The purpose of this paper is to present a stochastical approach, which analyse the torsional ground motion, induced by the spatial variability of seismic motions. For this purpose, a torsional ground motion analytical model is proposed and a normalised differential motion parameter is introduced. The approach regards the seismic motion as the combination of a travelling wave on the site (coherent component) and a zero mean randomizing factor that introduces a loss of correlation effect. The soil parameters as fundamental frequency and damping coefficient are integrating by modeling the coherent component with the commonly used Kanai-Tajimi power spectral density. The parametric analysis of the model shows an increase of the induced torsion with both the soil frequency and the motion scattering parameter, and a decrease with the separation distance, the apparent wave velocity and the correlation length. Finally, in order to test the proposed torsional ground motion model prediction, it is compared to the experimental results recorded by the EPRI LSST array in Lotung, Taiwan (Laouami and Labbe, 2002). The comparison leads to the identification of the model parameters for the Lotung soft site.

We have investigated the structure of (3-mercaptopropyl)sulfonate (MPS) monolayer self-assembled onto gold surfaces by quartz crystal microbalance with energy dissipation monitoring (QCM-D) and various electrochemical methods. QCM-D experiments show that the MPS monolayer behaves as a thin rigid film with a surfacic mass of 166 ng cm(-2). Interfacial capacitance measurements demonstrate that the MPS monolayer is a rather open structure that can be penetrated by the ionic species of the phosphate buffer electrolyte. From MPS reductive desorption experiments, MPS surface concentration corresponds to 4.6 x 10(-10) mol cm(-2), which represents 60% of the coverage reported for a densely packed thiol monolayer. Despite this low packing density, oxidation of catechol is strongly inhibited leading to voltammograms that are free ofdiffusional contribution. This unique behavior has been exploited to show that the MPS monolayer covers the entire gold surface with a surface coverage at least equal to theta = 0.9981, which means a very low number of MPS-free pinholes and/or defects. Kinetics of electron transfer toward soluble redox species has been studied using catechol as a neutral hydrophilic probe, but also ferrocyanide as hydrophilic anion and ferrocenemethanol as neutral hydrophobic molecule. It is proposed that the MPS monolayer provides a high kinetic barrier toward permeation of these species and that electron transfer mainly occurs by electron tunneling through the MPS monolayer.

We describe a new supramolecular architecture obtained by deposition of double‐stranded deoxyribonucleic acid (dsDNA) and chitosan derivatives on a thiolated gold surface. Surface plasmon resonance was used to monitor, in real time, the construction of the supramolecular architecture. Three chitosan derivatives were used, a quaternized N‐substituted by three methyl groups in a 40.0 mol%, and two others N‐substituted with an octyl chain in a 5.0 and 25.0 mol%. The multilayer formation depends on the degree of substitution of chitosan as well as on the nature of the substituents. The adsorption of dsDNA is slower than that of chitosan. The best immobilization of dsDNA is obtained by using a quaternized chitosan and dsDNA prepared in 0.050 M acetate buffer pH 5.00. The system is stable in buffer solution independently of the nature of the chitosan derivative. The effect of the nature of the electrolyte and ionic strength is also discussed.

Coproporphyrinogen oxidase (CPO) is an essential enzyme that catalyzes the sixth step of the heme biosynthetic pathway. Unusually for heme biosynthetic enzymes, CPO exists in two evolutionarily and mechanistically distinct families, with eukaryotes and some prokaryotes employing members of the highly conserved oxygen-dependent CPO family. Here, we report the crystal structure of the oxygen-dependent CPO from Saccharomyces cerevisiae (Hem13p), which was determined by optimized sulfur anomalous scattering and refined to a resolution of 2.0 A. The protein adopts a novel structure that is quite different from predicted models and features a central flat seven-stranded anti-parallel sheet that is flanked by helices. The dimeric assembly, which is seen in different crystal forms, is formed by packing of helices and a short isolated strand that forms a beta-ladder with its counterpart in the partner subunit. The deep active-site cleft is lined by conserved residues and has been captured in open and closed conformations in two different crystal forms. A substratesized cavity is completely buried in the closed conformation by the approximately 8-A movement of a helix that forms a lid over the active site. The structure therefore suggests residues that likely play critical roles in catalysis and explains the deleterious effect of many of the mutations associated with the disease hereditary coproporphyria.

Resume Les facettes articulaires posterieures participent a chaque articulation intervertebrale. Leurs caracteristiques anatomiques et biomecaniques expliquent leur role potentiel dans la genese de lombalgies chroniques, realisant le classique « syndrome des facettes ». Il n’existe cependant aucune donnee consensuelle, ni sur le plan diagnostique, ni sur le plan therapeutique, l’existence meme de ce syndrome etant controversee. Les donnees de la litterature permettent notamment de preciser l’interet des infiltrations intra-articulaires et leur realisation technique. Cependant les resultats specifiques d’un tel geste restent difficiles a interpreter, puisqu’il ne peut se concevoir qu’au sein d’un arsenal therapeutique plus large. En effet, le syndrome des facettes n’est qu’un des nombreux facteurs a l’origine de la lombalgie chronique, douleur-maladie qui necessite une prise en charge multidimensionnelle.

Build-up of enzyme–polyelectrolyte multilayer onto glassy carbon (GC) surfaces by electrostatic self-assembling method has been investigated. In order to functionalize GC surface by a starting negatively charged layer, two approaches have been carried out: (i) covalent linkage of phenyl acetic acid through electroreduction of 4-phenylacetic diazonium salt (GC A surface), and (ii) formation of a glucose oxidase (GOD) monolayer through an affinity reaction between a GOD conjugated antibody and a previously adsorbed antigen monolayer (GC B surface). GC A and GC B surfaces have been modified by a precursor film (PF) composed of one layer of poly(styrenesulfonate) (PSS) sandwiched between two layers of poly(dimethyldiallylammonium) (PDDA), which improves the further assembling of enzymes. GOD, used as a model enzyme, has been self-assembled with PDDA onto these GC/PF surfaces. Enzymatic activity of immobilized GOD has been electrochemically assessed layer-by-layer during the build-up of (GOD–PDDA) n multilayers. Cyclic voltammetry (CV) performed in the presence of excess glucose and using ferrocene derivatives as artificial redox mediators allowed to quantify the amount of electrically wired enzyme on the basis of kinetic models reported in literature. By using three mediators bearing different electrical charges we conclude that electrostatic interactions between the redox mediator and enzyme microenvironment play a key role in determining the rate of enzyme active site regeneration.

Beta-dystroglycan is expressed in a wide variety of tissues and has generally been reported with an Mr of 43 kDa, sometimes accompanied with a 31 kDa protein assumed to be a truncated product. This molecule was recently identified as the anomalous beta-dystroglycan expressed in various carcinoma cell lines. We produced and characterized a G5 polyclonal antibody specific to beta-dystroglycan that is directed against the C-terminal portion of the molecule. We provide evidence that beta-dystroglycan may vary in size and properties by studying different Xenopus tissues. Besides normal beta-dystroglycan with an Mr of 43 kDa in smooth and cardiac muscle and sciatic nerve extracts, we found it in skeletal muscle and brain proteins with an Mr of 38 and 65 kDa, respectively. Glycosylation properties and proteolytic susceptibilities of these different beta-dystroglycans are analysed and compared in this work. Crosslinking experiments with various beta-dystroglycan preparations obtained from skeletal and cardiac muscles and brain gave rise to specific new covalent products with Mr of 125 kDa (doublet band), or 120 and 130 kDa, or 140 and 240 kDa, respectively. We provide evidence, using various similar beta-dystroglycan preparations, that the immunoprecipitation procedure with G5 specific polyclonal antibody allows consistent pelleting of various dystrophin-family isoforms. Skeletal muscles from Xenopus reveals the presence of two distinct beta-dystroglycan complexes, one with dystrophin and another one which involves alpha-dystrobrevin. Cardiac muscle and brain from Xenopus are shown to contain three beta-dystroglycan complexes related to various dystrophin-family isoforms. Dystrophin or alpha-dystrobrevin or Dp71 were found in cardiac muscle and dystrophin or Dp180 or Up71 in brain. This variability in the relationship between beta-dystroglycan and dystrophin-family isoforms suggests that each protein – currently known as dystrophin associated protein – could not be present in each of these complexes.

RGD peptides (Arg–Gly–Asp) are known to promote cell adhesion. As a consequence, numerous materials have been functionalized using these peptides for several medical applications. We report herein the controlled functionalization of surfaces to study the influence of RGD density on cell selectivity. For this purpose, we selected a quartz crystal microbalance QCM-D as this technique allows real-time monitoring of cell adhesion to RGD surfaces. We observed that a critical spacing of nearly 40 nm between RGD ligands is required to observe selective cell adhesion whereas a higher density is not specific.

The purpose of this study was to perform an experimental analysis of the amplitude of full-scale spatial variability of seismic motions with regard to earthquake engineering. The LSST-Lotung array in Taiwan provides a good set of records for this type of study. Of interest are the free-field torsional seismic components induced by the spatial variability of seismic motions. In this study, three events have been considered: LSST-06, LSST-07 and LSST-16. In time domain analysis, the experimental results obtained show that when the separation distance increases, the induced torsion decreases, and the normalized differential motion parameter increases. Also, the results show that the stronger the event, in terms of maximum PGA, the larger the induced torsional amplitude and the smaller the induced normalized differential motion parameter.

International audience; We demonstrate the quartz crystal microbalance as a novel method to quantify the reaction yields and stability of the terminal conjugation of chemically complex molecules. Oxime ligation is identified as a facile, broadly applicable method for the reducing-end conjugation of glycosaminoglycans that overcomes the limited stability and yield of popular hydrazone ligation

In this paper, a stochastical approach for the investigation and the comprehension of the spatial variation of the seismic motions is presented. For this purpose, a coherency function analytical model is proposed. The approach regards the seismic motion as the combination of a traveling wave on the site (coherent component) and a zero mean randomizing factor that introduces an incoherence effect. The soil parameters as fundamental frequency and damping coefficient are integrating by modeling the coherent component with the commonly used Kanai-Tajimi power spectral density. The parametric analysis of the model shows an increase of the coherency with the increase of (i) the apparent propagation velocity of the motions on the ground surface, and (ii) the correlation length. On the other hand, the coherency decrease with the increase of: (i) the frequency content of the motion, (ii) the separation distance between stations and (iii) the scattering parameter which is the randomizing factor standard deviation. Finally, in order to test the proposed model prediction, its coherency function is compared to empirical results obtained on the EPRI LSST array in Lotung, Taiwan (Abrahamson NA, Shneider JF, Stepp JC. Earthquake Spectra 1991; 7:1–28). The comparison shows that the proposed model fits the spatial variability of seismic motions on Lotung site. In the absence of spatially recorded seismic data on a site, the proposed analytical model can be utilised for the description of the spatial variability of the seismic motions for the seismic response analysis of structures with large dimensions as pipes, bridges, tunnels…etc.

The amperometric response toward phenol of PPO-based rotating disk bioelectrodes is analyzed on the basis of a kinetic model taking into account internal and external mass transport effects and a CEC' electroenzymatic mechanism. Monophenolase activity of PPO catalyses the oxidation of phenol to o-quinone (step C). o-Quinone can then enter an amplification recycling process involving electrochemical reduction (step E) and enzymatic reoxidation (step C': catecholase activity). The rate-limiting steps such as monophenolase activity, catecholase recycling, permeability of the membrane, and activity and accessibility of the catalytic enzyme sites are theoretically considered and experimentally demonstrated for different electrode configurations including PPO immobilized in Laponite hydrogels and layer-by-layer self-assembled multilayers of PPO and poly(diallyldimethylammonium).

A feasibility study in view of a future industrial development of a phenol biosensor is presented. The biosensor construction is based on the electropolymerization of a pyrrole amphiphilic monomer–tyrosinase (EC.1.14.18.1) mixture previously adsorbed on a glassy carbon electrode surface. The optimized biosensor provides a low detection limit (10 nM) and a linear response up to 10 μM of phenol. The procedure allows the construction of biosensors exhibiting very reproducible characteristics. These bioelectrodes are characterized by exceptional long-term stability since they could be stored for 1 year without significant loss of their electroenzymatic activity.

The association of an inorganic/organic composite matrix with a permselective poly(4-vinylpyridine-co-styrene) membrane allows to obtain a selective glucose biosensor, allowing a sensitivity of 30 mA M−1 cm−2, for a linear dynamic range from 10−5 M to 1.5 mM. Moreover, the combined use of such permselective membranes with a bienzymatic system, glucose oxidase/polyphenol oxidase, has demonstrated that the effect of electroactive interferent species such as ascorbate, urate and p-acetaminophen, can be entirely removed.

Amperometric catechol biosensors can be constructed by drying onto the surface of a glassy carbon rotating-disk electrode an aqueous sol of synthetic laponite clay containing controlled amounts of polyphenol oxidase (PPO) and polycationic oligosilasesquioxane additive. The procedure allows the electrode surface to be coated with composite enzyme–laponite clay films exhibiting improved adhesion, enhanced mechanical strength and high enzymatic activity. Electrodes prepared in this manner can be used to detect catechol in the range 0.5 nM to 10 μM. The low detection limit of 0.5 nM results from an efficient signal amplification as a consequence of the electrochemical recycling of catechol substrate. An intrinsic amplification factor of 3.35 has been measured. The observed responses from such an electrode as a function of applied potential, enzyme activity and electrode rotation rate are in excellent agreement with theory. From a comparison of the experimental results with theory, we are able to characterize diffusion and enzyme kinetics in the enzymatic layer. The results are consistent with a microporous structure of the enzymatic layer in which microchannels are distributed. Diffusion of catechol substrate and orthoquinone product occurs within the microchannels filled by electrolyte and can be described using a pinhole model. The study shows that only a fraction of PPO, the one which is entrapped in open micropores with interconnected microchannels, is accessible to catechol substrate while keeping its full enzymatic activity. The other fraction should correspond to inaccessible proteins enclosed within the walls of microchannels.

Electrode surface modification by organo-inorganic layered coatings can be achieved readily by drying a completely delaminated laponite clay sol mixed with polycationic silasesquioxane oligomers. Oligosilsesquioxanes were synthesized by hydrolytic polycondensation of trialkoxysilanes bearing an alkylamino or alkyltrimethylammonium function. Films of excellent quality with exceptional adhesion and mechanical properties can be obtained. The intercalation of organosiloxane oligomers is accompanied by the expansion of the film and by the existence of a mesoporosity as shown by XRD measurements and N 2 adsorption experiments. The ion-exchange properties of the resulting coatings as well as permeation of neutral molecules were studied in aqueous and non-aqueous electrolytes as a function of the oligomer loading. For oligomer loadings higher than the cation-exchange capacity (cec) of laponite, the coatings behave as anion-exchangers which allows the binding a wide range of redox anions. Incorporated anions remain electroactive not only in aqueous but also in non aqueous electrolytes as a consequence of a fixed pore size and permanent interlayer spacing of oligomer-expanded laponite. On the other hand intercalation of oligomers allows us to modulate the permeability of the coating as shown by permeation experiments using neutral electroactive probes in non aqueous electrolytes. In the field of electroanalysis, amperometric biosensors made by the entrapment of glucose oxidase inside the hybrid material have been investigated successfully. Such enzymatic films exhibit enhanced analytical performances as compared with those obtained using native sodic laponite. The potential applications of this new hybrid material in the field of electrocatalysis have been exemplified by the electroprecipitation of catalytic nanoparticles such as Pt(0) obtained from the incorporation of the anionic precursor PtCl 4 2− .

A new mixed membrane material for amperometric glucose biosensors, based on immobilization of glucose oxidase (GOD) in inorganic laponite gels followed by an enzyme crosslinking through glutaraldehyde (GA) is investigated. This method gives the possibility to modulate the enzyme loading in the biomembrane, the corresponding sensitivities obtained being directly proportional to the enzyme content in the membrane. Thus, with a GOD/laponite ratio of 3.3, sensitivities reach up to 132 mA M −1 cm −2 for a linear dymamic range from 10 −2 to 20 mM. Effects of oxygen and temperature have been investigated. The analysis of the bioelectrode characteristics shows a good permeability of this inorganic/organic enzymatic membrane. A specific design, combining a Nafion membrane and incorporation of polyphenol oxydase, allows to reduce the effects of interfering species such as ascorbate, urate and acetaminophen by a factor 4.

A quartz crystal microbalance technique with dissipation monitoring and a complementary optical microscopy technique were used for monitoring the capture and release of specific cells on a surface displaying a bifunctional molecular device, composed of a molecular scaffold endowed with the cell recognition property of an RGD ligand and a β-CD/Fc redox-switchable system.

This paper presents an analysis of impedimetric measurements and their variations due to interaction with biomolecules on platinum electrodes functionalized with polymeric layers containing antibodies. The behavior of electrodes functionalized either with aminopolysiloxanes deposited by a dip coating process or with an electropolymerized polypyrrole is compared. Best results were obtained using polypyrrole film based electrodes; these are discussed in terms of better permeability for the analyte.

A new bienzymatic electrode for glucose sensing has been constructed with the aid of the sol−gel process. This mediatorless sensor was made by the simultaneous immobilization of graphite microparticles and two enzymes (horseradish peroxidase (HRP) and glucose oxidase (GOD)) in a silica gel matrix. The amperometric detection of glucose was assayed by potentiostating the biosensor at 0 V vs SCE in order to reduce the enzymically generated H2O2. The active graphite particles evenly dispersed within the silica gel matrix establish an efficient electrical communication between the electrode surface and the HRP active center. The effect of graphite and HRP amounts have been investigated in order to improve the analytical characteristics of the amperometric H2O2 biosensor. For determination of glucose, a bilayer structure where HRP and GOD were immobilized in two separated silica films exhibited the higher analytical performances.

The self-aggregation properties of a pyrrole-substituted cationic surfactant have been studied using different techniques, including conductivity and surface tension measurements, potentiometry with a surfactant-selective electrode and cyclic voltammetry. Potentiometry gave good results for the determination of its critical micelle concentration (CMC) as well in pure water as in electrolytic media. Furthermore, in spite of the highly irreversible oxidation of the pyrrole group contained in the surfactant, cyclic voltammetry afforded a fast and valuable estimation of the CMC from peak current and peak potential variations.