Etudes thermochimiques à haute température par spectrométrie de masse : dispositif pour mesures au moyen de cellules d'effusion multiples

Le dispositif décrit a été réalisé dans le but d'effectuer des mesures comparatives directes de pressions de vapeur sur cellules d'effusion multiples, le détecteur de flux étant un spectromètre de masse. La reproductibilité des mesures a été étudiée notamment en fonction du positionnement mécanique des cellules et des conditions d'ionisation du jet moléculaire dans la source d'ions. Les essais présentés montrent que cette méthode peut être appliquée de manière satisfaisante à la détermination d'activités thermodynamiques dans des systèmes à haute température

Development and Evaluation of a Miniaturized Taste Sensor Chip

A miniaturized taste sensor chip was designed for use in a portable-type taste sensing system. The fabricated sensor chip (40 mm × 26 mm × 2.2 mm) has multiple taste-sensing sites consisting of a poly(hydroxyethyl methacrylate) hydrogel with KCl as the electrolyte layer for stability of the membrane potential and artificial lipid membranes as the taste sensing elements. The sensor responses to the standard taste substances showed high accuracy and good reproducibility, which is comparable with the performance of the sensor probe of the commercialized taste sensing system. Thus, the fabricated taste sensor chip could be used as a key element for the realization of a portable-type taste sensing system

A Biosensor for Urea from Succinimide-Modified Acrylic Microspheres Based on Reflectance Transduction

New acrylic microspheres were synthesised by photopolymerisation where the succinimide functional group was incorporated during the microsphere preparation. An optical biosensor for urea based on reflectance transduction with a large linear response range to urea was successfully developed using this material. The biosensor utilized succinimide-modified acrylic microspheres immobilized with a Nile blue chromoionophore (ETH 5294) for optical detection and urease enzyme was immobilized on the surface of the microspheres via the succinimide groups. No leaching of the enzyme or chromoionophore was observed. Hydrolysis of the urea by urease changes the pH and leads to a color change of the immobilized chromoionophore. When the color change was monitored by reflectance spectrophotometry, the linear response range of the biosensor to urea was from 0.01 to 1,000 mM (R2 = 0.97) with a limit of detection of 9.97 μM. The biosensor response showed good reproducibility (relative standard deviation = 1.43%, n = 5) with no interference by major cations such as Na+, K+, NH4+ and Mg2+. The use of reflectance as a transduction method led to a large linear response range that is better than that of many urea biosensors based on other optical transduction methods

Determination of Ammonium Ion Using a Reagentless Amperometric Biosensor Based on Immobilized Alanine Dehydrogenase

The use of the enzyme alanine dehydrogenase (AlaDH) for the determination of ammonium ion (NH4+) usually requires the addition of pyruvate substrate and reduced nicotinamide adenine dinucleotide (NADH) simultaneously to effect the reaction. This addition of reagents is inconvenient when an enzyme biosensor based on AlaDH is used. To resolve the problem, a novel reagentless amperometric biosensor using a stacked methacrylic membrane system coated onto a screen-printed carbon paste electrode (SPE) for NH4+ ion determination is described. A mixture of pyruvate and NADH was immobilized in low molecular weight poly(2-hydroxyethyl methacrylate) (pHEMA) membrane, which was then deposited over a photocured pHEMA membrane (photoHEMA) containing alanine dehydrogenase (AlaDH) enzyme. Due to the enzymatic reaction of AlaDH and the pyruvate substrate, NH4+ was consumed in the process and thus the signal from the electrocatalytic oxidation of NADH at an applied potential of +0.55 V was proportional to the NH4+ ion concentration under optimal conditions. The stacked methacrylate membranes responded rapidly and linearly to changes in NH4+ ion concentrations between 10–100 mM, with a detection limit of 0.18 mM NH4+ ion. The reproducibility of the amperometrical NH4+ biosensor yielded low relative standard deviations between 1.4–4.9%. The stacked membrane biosensor has been successfully applied to the determination of NH4+ ion in spiked river water samples without pretreatment. A good correlation was found between the analytical results for NH4+ obtained from the biosensor and the Nessler spectrophotometric method

Functionalized polypyrroles : a sophisticated glue for the immobilization and electrical wiring of enzymes

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An Auger depth profile analysis of a sputtered Fe-Ti multilayer structure

International audienceA deconvolution process is used to discuss the peak-to-peak height curves obtained during the depth profile analysis of a sputtered Fe-Ti multilayer sample. The modifications induced by the inelastic mean free path, the roughness and the mixing effect are taken into account and enable more accurate information to be obtained on the main constituent signals. In addition, the positions of the C, O and Ar impurities are analysed

CONTROLLED FABRICATION OF GLUCOSE AND CATECHOL MICROBIOSENSORS VIA ELECTROPOLYMERIZED BIOTINYLATED POLYPYRROLE FILMS

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A Biotinylated Conducting Polypyrrole for the Spatially Controlled Construction of an Amperometric Biosensor

International audienceA new biotin derivative functionalized by an electropolymerizable pyrrole group has been synthesized. The electrooxidation of this biotin pyrrole has allowed the formation of biotinylated conducting polypyrrole films in organic electrolyte. Gravimetric measurements based on a quartz crystal microbalance, modified by the biotinylated polymer, revealed an avidin−biotin-specific binding at the interface of polymer−solution. The estimated mass increase corresponded to the anchoring of 1.5 avidin monolayers on the polypyrrole surface. In addition, the subsequent grafting of biotinylated glucose oxidase was corroborated by electrochemical permeation studies. Enzyme multilayers composed of glucose oxidase or polyphenol oxidase were elaborated on the electrode surface modified by the biotinylated polypyrrole film. The amperometric response of the resulting biosensors to glucose or catechol has been studied at +0.6 or −0.2 V vs SCE, respectively

Mesoporous TiO2 films: New catalytic electrode fabricating amperometric biosensors based on oxidases

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