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21.
报道了一种新的L-氨基酸氧化酶电极,这种酶电极系由氨气敏电极和以氨基化玻璃布为载体的酶膜所组成;研究了固定化条件对酶膜活性的影响以及底物浓度、温度和pH对电极响应特性的影响。该电极在6.0×10^-5~4.0×10^-3mol/L的底物浓度范围内呈良好的线性关系,检测下限为5.0×10^-5mol/L。在最宜条件下,酶电极具有良好的稳定性。 相似文献
22.
A simple direct enzyme immunoassay for semiquantitative detec tion of antibodies is suggested. It is based on the difference
in diffusion rates in a gel for a synthetic low-mol-wt antigen and of its complexes with antibodies to be detected. Sensitivity
and specificity of the devel oped assay are equal to an ELISA method. The assay has been tested with antibodies against HIV
protein gp41 in rabbit serum. Possible applications and limitations of the method are discussed. 相似文献
23.
Nanometric vanadium antimonate, VSbO4, was prepared by mechanical milling from Sb2O3 and V2O5 and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mossbaüer spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS) techniques. Its reactivity towards lithium was examined by testing Li/VSbO4 cells under galvanostatic and potentiostatic regimes. The amount of Li inserted was found to be consistent with a two-step process involving the reactions (i) VSbO4+8 Li→Sb+V+4 Li2O and (ii) Sb+3 Li→Li3Sb, the former being virtually irreversible and the latter reversible as suggested by the shape of the anodic and cathodic curves. Ex situ XPS measurements of the discharged and charged electrode provided direct evidence of the formation of alloyed Sb and confirmed the results of the potentiostatic curves regarding the irreversible or reversible character of the previous reactions. The Li/VSbO4 cell exhibited acceptable electrochemical performance, which surpassed that of other Sb-based compounds as the likely result of the formation of V and its associated enhanced electrode conductivity. 相似文献
24.
Michael P Bokoch 《Analytica chimica acta》2004,519(1):47-55
Cholesterol oxidase is immobilized in electrode-supported lipid bilayer membranes. Platinum electrodes are initially modified with a self-assembled monolayer of thiolipid. A vesicle fusion method is used to deposit an outer leaflet of phospholipids onto the thiolipid monolayer forming a thiolipid/lipid bilayer membrane on the electrode surface. Cholesterol oxidase spontaneously inserts into the electrode-supported lipid bilayer membrane from solution and is consequently immobilized to the electrode surface. Cholesterol partitions into the membrane from buffer solutions containing cyclodextrin. Cholesterol oxidase catalyzes the oxidation of cholesterol by molecular oxygen, forming hydrogen peroxide as a product. Amperometric detection of hydrogen peroxide for continuous solution flow experiments are presented, where flow was alternated between cholesterol solution and buffer containing no cholesterol. Steady-state anodic currents were observed during exposures of cholesterol solutions ranging in concentration from 10 to 1000 μM. These data are consistent with the Michaelis-Menten kinetic model for oxidation of cholesterol as catalyzed by cholesterol oxidase immobilized in the lipid bilayer membrane. The cholesterol detection limit is below 1 μM for cholesterol solution prepared in buffered cyclodextrin. The response of the electrodes to low density lipoprotein solutions is increased upon addition of cyclodextrin. Evidence for adsorption of low density lipoprotein to the electrode surface is presented. 相似文献
25.
Bulk-modified epoxy-graphite tyrosinase biosensors were fabricated by four different procedures. The influence of these fabrication procedures on the analytical performance of the enzyme electrode in an amperometric wall-jet flow cell has been studied. The bioprobe performance is assessed by cyclic voltammetry. Higher current densities and narrower peaks were obtained when the enzyme was introduced in the dry state into the epoxy-graphite material, instead of introducing it previously dissolved in the buffer. In the F1 system responses of 11.79 μA cm−2 and 1.43 μA cm−2 are then obtained for catechol and phenol respectively for 50 μL injections of 20 μM solutions. Moreover, if gold/palladium is introduced into the epoxy-graphite, a further increase in current is achieved resulting in 27.70μA cm−2 and 4.90μA cm−2for catechol and phenol, respectively. This biosensor can operate in aqueous as well as in mixed aqueous-organic environments. 相似文献
26.
Emmanuel Burgos 《Tetrahedron letters》2004,45(17):3465-3469
4-deoxy-4-Phosphonomethyl-d-erythronate, an isosteric and hydrolytically stable analogue of the known ribose-5-phosphate isomerase inhibitor 4-deoxy-4-phospho-d-erythronate, was obtained by a 14-step synthesis from d-arabinose through an highly improved synthesis of the precursor 5-deoxy-5-phosphonomethyl-d-arabinose. The title compound appears as the first stable and potent competitive inhibitor of the enzyme catalyzed isomerization of ribose-5-phosphate to d-ribulose-5-phosphate (Ki=74 μM, Km/Ki=100), exhibiting only a 3-fold weaker inhibitory activity than its phosphate analogue. 相似文献
27.
E.?V.?TsipisEmail author V.?V.?Kharton I.?A.?Bashmakov E.?N.?Naumovich J.?R.?Frade 《Journal of Solid State Electrochemistry》2004,8(9):674-680
Developments of intermediate-temperature solid oxide fuel cells (IT SOFCs) require novel anode materials with a high electrochemical activity at 800–1070 K. The polarization of cermet anodes, made of nickel, ceria and yttria-stabilized zirconia (YSZ) and applied onto a YSZ solid electrolyte, can be significantly reduced by catalytically active ceria additions, the relative role of which increases with decreasing temperature. Further improvement is observed when using Ce0.8Gd0.2O2–
(CGO) having a high oxygen ionic conductivity instead of undoped ceria, owing to enlargement of the electrochemical reaction zone. Nanocrystalline CGO powders with grain sizes of 8–35 nm were thus synthesized via the cellulose-precursor technique and introduced into Ni–CGO–YSZ cermets, and tested in contact with a (La0.9Sr0.1)0.98Ga0.8Mg0.2O3–
(LSGM) electrolyte at 873–1073 K. The results showed that the anode performance can be enhanced by additional surface activation, in particular by impregnation with a Ce-containing solution, and also by incorporation of YSZ, which probably acts as a cermet-stabilizing component. The overpotential of the surface-modified Ni–CGO (25 wt%–75 wt%) anode in a 10% H2/90% N2 atmosphere was approximately 110 mV at 1073 K with a current density of 200 mA/cm2.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003 相似文献
28.
Enzyme heterobilayer-modified electrodes were fabricated by successively covalently binding to the surface of a tin(IV) oxide plate horseradish peroxidase (HRP), then an oxidase (lactate, pyruvate or cholesterol oxidase or uricase), which liberates hydrogen peroxide by reaction with the respective substrate. The cooperative action of oxidase-HRP leads to an efficient amperometric sensor system with the minimum amount of enzyme immobilized on an electrode. 相似文献
29.
The construction and response of an immobilized enzyme modified electrode as an amperometric sensor is described. Xanthine oxidase was adsorbed on a carbon paste electrode and physically entrapped with a semipermeable membrane. Uric acid, the product of the enzymatic reaction, was oxidized electrochemically at +0.4 V vs. Ag/AgCl, yielding a steady-state current directly related to the bulk concentration of the substrate. Hypoxanthine and xanthine were determined in the range 5–100 μM at Ph 7.2 with good precision. Interferences are discussed. 相似文献
30.
J. Tolchard 《Journal of solid state chemistry》2007,180(10):2808-2815
The chemical and physical compatibility of SrCeO3 is investigated with respect to LaMO3 (M=Mn, Fe, Co) and La2−xSrxNiO4 (x=0, 0.8), via the reaction of fine-grained powder compacts and solid-state diffusion couples. Compositions were chosen so as to give predictive insight into possible candidate materials for all-oxide electrochemical devices. Results show the primary reaction in these systems to be the dissolution of SrO from SrCeO3 into the LaMO3/La2−xSrxNiO4, and corresponding formation of La-doped CeO2. Reaction kinetics are observed to be relatively fast, with element profiles suggesting the diffusion of Sr2+ in ceria to be surprisingly rapid. It is demonstrated that perovskite starting materials represent poor candidates for use with SrCeO3, reacting completely to form Ruddlesden-Popper/K2NiF4 type oxides. Reaction with La2NiO4 is less pronounced, and formation of secondary phases suppressed for the composition La1.2Sr0.8NiO4. It is thus concluded that Ruddlesden-Popper type oxides represent good candidate materials for use with a SrCeO3-based electrolytes when doped with appropriate levels of Sr. 相似文献