23 research outputs found
Development of an Ion Sensitive Field Effect Transistor Based Urea Biosensor with Solid State Reference Systems
Ion sensitive field-effect transistor (ISFET) based urease biosensors with solid state reference systems for single-ended and two-ended differential readout electronics were investigated. The sensing membranes of the biosensors were fabricated with urease immobilized in a conducting polymer-based matrix. The responses of 12.9âŒ198.1 mV for the urea concentrations of 8âŒ240 mg/dL reveal that the activity of the enzyme was not significantly decreased. Biosensors combined with solid state reference systems were fabricated, and the evaluation results demonstrated the feasibility of miniaturization. For the differential system, the optimal transconductance match for biosensor and reference field-effect transistors (REFET) pair was determined through the modification of the membranes of the REFETs and enzyme field-effect transistors (EnFETs). The results show that the transconductance curve of polymer based REFET can match with that of the EnFET by adjusting the photoresist/Nafionâą ratio. The match of the transconductance curves for the differential pairs provides a wide dynamic operating measurement range. Accordingly, the miniaturized quasi-reference electrode (QRE)/REFET/EnFET combination with differential arrangement achieved similar urea response curves as those measured by a conventional large sized discrete sensor
Solid-state reference electrodes based on carbon nanotubes and polyacrylate membranes
A novel potentiometric solid-state reference electrode containing single-walled carbon nanotubes as the transducer layer between a polyacrylate membrane and the conductor is reported here. Single-walled carbon nanotubes act as an efficient transducer of the constant potentiometric signal originating from the reference membrane containing the Ag/AgCl/Clâ ions system, and they are needed to obtain a stable reference potentiometric signal. Furthermore, we have taken advantage of the light insensitivity of single-walled carbon nanotubes to improve the analytical performance characteristics of previously reported solid-state reference electrodes. Four different polyacrylate polymers have been selected in order to identify the most efficient reservoir for the Ag/AgCl system. Finally, two different arrangements have been assessed: (1) a solid-state reference electrode using photo-polymerised n-butyl acrylate polymer and (2) a thermo-polymerised methyl methacrylate:n-butyl acrylate (1:10) polymer. The sensitivity to various salts, pH and light, as well as time of response and stability, has been tested: the best results were obtained using single-walled carbon nanotubes and photo-polymerised n-butyl acrylate polymer. Water transport plays an important role in the potentiometric performance of acrylate membranes, so a new screening test method has been developed to qualitatively assess the difference in water percolation between the polyacrylic membranes studied. The results presented here open the way for the true miniaturisation of potentiometric systems using the excellent properties of single-walled carbon nanotubes
Microstructural optimization of HP alloy for high temperature applications
Lâobjectif de ce travail est dâamĂ©liorer la durĂ©e de vie en fluage dâun alliage rĂ©sistant Ă haute tempĂ©rature. Lâalliage Ă©tudiĂ©, nommĂ© « C », appartient Ă la classe des aciers austĂ©nitiques de type HP utilisĂ©s pour la fabrication des tubes de reformage. LâĂ©volution microstructurale de lâalliage « C » a Ă©tĂ© Ă©tudiĂ©e dans une vaste gamme de tempĂ©ratures, sâĂ©tendant de 700 Ă 1040°C pour des temps de vieillissement allant jusquâĂ 1000 h. La caractĂ©risation de ces Ă©tats vieillis a Ă©tĂ© rĂ©alisĂ©e au moyen de la microscopie Ă©lectronique (MEB-FEG, MET) et de la diffraction des rayons X. Lâaccent a Ă©tĂ© mis sur une caractĂ©risation fine de la prĂ©cipitation secondaire prĂ©sente Ces rĂ©sultats ont ensuite Ă©tĂ© utilisĂ©s afin dâidentifier les conditions thermiques optimales pour lâaffinement de la prĂ©cipitation en vue dâamĂ©lioration du comportement macroscopique de lâalliage. La cinĂ©tique de prĂ©cipitation a Ă©tĂ© modĂ©lisĂ©e Ă lâaide du logiciel PRISMA ThermoCalc. Un bon accord entre la simulation et les mesures expĂ©rimentales a pu ĂȘtre obtenu.Dans la gamme de tempĂ©ratures Ă©tudiĂ©e, la prĂ©cipitation secondaire est majoritairement constituĂ©e de deux carbures : M23C6 (M=Cr, Fe) et NbC. En condition de service (980°C), la croissance du M23C6 est rapide. La coalescence des prĂ©cipitĂ©s survient dĂšs 200 h de vieillissement. Nous avons prouvĂ© quâun vieillissement Ă des tempĂ©ratures plus basses (700-750°C) permet dâaffiner cette prĂ©cipitation. De plus, notre Ă©tude a montrĂ© lâefficacitĂ© dâun prĂ©traitement Ă des tempĂ©ratures basses, effectuĂ© avant la mise en service du matĂ©riau Ă 980°C. Une nette amĂ©lioration de la rĂ©sistance en fluage dans des essais accĂ©lĂ©rĂ©s a Ă©tĂ© obtenue pour lâalliage « C » ayant subi le prĂ©traitement citĂ© ci-dessus. Outre lâaffinement et le retardement de la coalescence du M23C6, la prĂ©sence dâune prĂ©cipitation nanomĂ©trique du NbC sur des lignes de dislocations est probablement Ă lâorigine de cet effet.The purpose of this work is to optimise the microstructure of a creep-resistant alloy of the type HP, called âCâ (industrial denomination). These austenitic steels are used for the manufacture of reformer tubes. The microstructural evolution of the alloy "C" has been studied in a wide range of temperatures, ranging from 700 to 1040 °C for aging times up to 1000 h. The characterization of these aged states was performed using electron microscopy (FEG-SEM, TEM) and X-ray diffraction, with emphasis on a detailed characterization of this secondary precipitation. This knowledge was then used to identify the optimal thermal conditions for the refinement of precipitation to improve the macroscopic behaviour of the alloy. The precipitation kinetics was modelled using the PRISMA ThermoCalc. A good agreement between simulation and experimental measurements has been obtained.In the studied range of temperature, the secondary precipitation consists mainly of two carbides M23C6 (M = Cr, Fe) and NbC. In the service conditions (980°C), the growth of M23C6 is fast. The coalescence of the precipitates starts after only 200h of aging. Aging at lower temperatures (700-750°C) refines this precipitation. Our study showed the efficacy of pre-treatment of the alloy at low temperatures, before the service of the material at 980°C. In the alloy "C", treated in such conditions, a significant increase in creep resistance was obtained in accelerated testing. In addition to refinement of the secondary precipitation and delaying the effects of coalescence of M23C6, the presence of a nanoscale precipitation of NbC on dislocation lines is probably the origin of this effect
Optimisation microstructurale dâun acier HP pour des applications Ă haute tempĂ©rature
The purpose of this work is to optimise the microstructure of a creep-resistant alloy of the type HP, called âCâ (industrial denomination). These austenitic steels are used for the manufacture of reformer tubes. The microstructural evolution of the alloy "C" has been studied in a wide range of temperatures, ranging from 700 to 1040 °C for aging times up to 1000 h. The characterization of these aged states was performed using electron microscopy (FEG-SEM, TEM) and X-ray diffraction, with emphasis on a detailed characterization of this secondary precipitation. This knowledge was then used to identify the optimal thermal conditions for the refinement of precipitation to improve the macroscopic behaviour of the alloy. The precipitation kinetics was modelled using the PRISMA ThermoCalc. A good agreement between simulation and experimental measurements has been obtained.In the studied range of temperature, the secondary precipitation consists mainly of two carbides M23C6 (M = Cr, Fe) and NbC. In the service conditions (980°C), the growth of M23C6 is fast. The coalescence of the precipitates starts after only 200h of aging. Aging at lower temperatures (700-750°C) refines this precipitation. Our study showed the efficacy of pre-treatment of the alloy at low temperatures, before the service of the material at 980°C. In the alloy "C", treated in such conditions, a significant increase in creep resistance was obtained in accelerated testing. In addition to refinement of the secondary precipitation and delaying the effects of coalescence of M23C6, the presence of a nanoscale precipitation of NbC on dislocation lines is probably the origin of this effect.Lâobjectif de ce travail est dâamĂ©liorer la durĂ©e de vie en fluage dâun alliage rĂ©sistant Ă haute tempĂ©rature. Lâalliage Ă©tudiĂ©, nommĂ© « C », appartient Ă la classe des aciers austĂ©nitiques de type HP utilisĂ©s pour la fabrication des tubes de reformage. LâĂ©volution microstructurale de lâalliage « C » a Ă©tĂ© Ă©tudiĂ©e dans une vaste gamme de tempĂ©ratures, sâĂ©tendant de 700 Ă 1040°C pour des temps de vieillissement allant jusquâĂ 1000 h. La caractĂ©risation de ces Ă©tats vieillis a Ă©tĂ© rĂ©alisĂ©e au moyen de la microscopie Ă©lectronique (MEB-FEG, MET) et de la diffraction des rayons X. Lâaccent a Ă©tĂ© mis sur une caractĂ©risation fine de la prĂ©cipitation secondaire prĂ©sente Ces rĂ©sultats ont ensuite Ă©tĂ© utilisĂ©s afin dâidentifier les conditions thermiques optimales pour lâaffinement de la prĂ©cipitation en vue dâamĂ©lioration du comportement macroscopique de lâalliage. La cinĂ©tique de prĂ©cipitation a Ă©tĂ© modĂ©lisĂ©e Ă lâaide du logiciel PRISMA ThermoCalc. Un bon accord entre la simulation et les mesures expĂ©rimentales a pu ĂȘtre obtenu.Dans la gamme de tempĂ©ratures Ă©tudiĂ©e, la prĂ©cipitation secondaire est majoritairement constituĂ©e de deux carbures : M23C6 (M=Cr, Fe) et NbC. En condition de service (980°C), la croissance du M23C6 est rapide. La coalescence des prĂ©cipitĂ©s survient dĂšs 200 h de vieillissement. Nous avons prouvĂ© quâun vieillissement Ă des tempĂ©ratures plus basses (700-750°C) permet dâaffiner cette prĂ©cipitation. De plus, notre Ă©tude a montrĂ© lâefficacitĂ© dâun prĂ©traitement Ă des tempĂ©ratures basses, effectuĂ© avant la mise en service du matĂ©riau Ă 980°C. Une nette amĂ©lioration de la rĂ©sistance en fluage dans des essais accĂ©lĂ©rĂ©s a Ă©tĂ© obtenue pour lâalliage « C » ayant subi le prĂ©traitement citĂ© ci-dessus. Outre lâaffinement et le retardement de la coalescence du M23C6, la prĂ©sence dâune prĂ©cipitation nanomĂ©trique du NbC sur des lignes de dislocations est probablement Ă lâorigine de cet effet
ESCRT proteins restrict constitutive NF-kappa B signaling by trafficking cytokine receptors
Because signaling mediated by the transcription factor nuclear factor kappa B (NF-kappa B) is initiated by ligands and receptors that can undergo internalization, we investigated how endocytic trafficking regulated this key physiological pathway. We depleted all of the ESCRT (endosomal sorting complexes required for transport) subunits, which mediate receptor trafficking and degradation, and found that the components Tsg101, Vps28, UBAP1, and CHMP4B were essential to restrict constitutiveNF-kappa B signaling in human embryonic kidney 293 cells. In the absence of exogenous cytokines, depletion of these proteins led to the activation of both canonical and noncanonical NF-kappa B signaling, as well as the induction of NF-kappa B-dependent transcriptional responses in cultured human cells, zebrafish embryos, and fat bodies in flies. These effects depended on cytokine receptors, such as the lymphotoxin beta receptor (LT beta R) and tumor necrosis factor receptor 1 (TNFR1). Upon depletion of ESCRT subunits, both receptors became concentrated on and signaled from endosomes. Endosomal accumulation of LT beta R induced its ligand-independent oligomerization and signaling through the adaptors TNFR-associated factor 2 (TRAF2) and TRAF3. These data suggest that ESCRTs constitutively control the distribution of cytokine receptors in their ligand-free state to restrict their signaling, which may represent a general mechanism to prevent spurious activation of NF-kappa B