摘要:

This report demonstrates the use of the nerve bundle from the crayfish walking leg for the detection and assay of local anesthetics (LAs). Detection is achieved by monitoring the disappearance of the compound action potential (CAP) upon application of the local anesthetics to the nerves, pinned in a specially designed flow cell. CAP firing is induced with an electrical current pulse applied to the nerve bundle. Dose-response curves for the LAs tetracaine, lidocaine and procaine are constructed and factors which affect the detection are discussed. The application of this procedure to the screening for neurotoxicity and neuromodulatory activity of new drugs and natural product extracts is proposed.

ISSN:0003-2719    

DOI:10.1080/00032719308017412

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Amperometric bioelectrodes based on carbon paste mixed with glucose oxidase (GOX) and dimethylferrocene (DMFc), are characterized by using cyclic voltammetry, potential step chronoamperometry and amperometry at a rotating disk electrode. The catalytic process appears to be highly dependent on the amount of DMFc. Kinetic control, internal diffusion control and external diffusion control can be obtained only by varying the amount of incorporated DMFc. It was shown that the Eadie-Hofstee plot is a particularly useful tool in diagnosis of diffusional limitations. The high efficiency of electrochemical regeneration of high amounts of DMFc* surrounding GOX solves the problem of co-substrate transport. The catalytic oxidation current of ascorbic acid was highly diminished by casting a lipid/Nafion membrane and totally eliminated by treatment of the sample with hydrogen peroxide prior to measurement.

ISSN:0003-2719    

DOI:10.1080/00032719308017413

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An amperometric enzyme electrode for L-Alanine determination was developed. The probe is based on a platinum electrode which senses the hydrogen peroxide produced by the enzymatic reactions catalyzed by two enzymes: alanine aminotransferase (ALT) and glutamate oxidase. Both the enzymes were immobilized on polymeric membrane supports. Interferences were discriminated by additional protective membranes. Buffer, pH, cosubstrate, temperature and immobilization procedures were optimized. The probe response was linear in the concentration range 10−5– 10−3mol/L with a detection limit of 2·10−6mol/L.

ISSN:0003-2719    

DOI:10.1080/00032719308017414

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An amperometric enzyme electrode based on peroxide detection has been prepared for protein determination. A trienzyme system immobilized on two stacked membranes was used. L-aminoacid oxidase and leucine aminopeptidase were coimmobilized on one membrane in contact with the platinum anode, whereas the second membrane, directly in contact with the reaction medium, had immobilized trypsin. In a first step, the sensor equipped only with the bienzyme membrane was tested with two peptides, then with protein hydrolysates, and optimized conditions were determined. Casein could be assayed with the three-enzyme system within a linear concentration range of 0.1–4 mg/mL with response-times between 5 and 9 minutes.

ISSN:0003-2719    

DOI:10.1080/00032719308017415

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Enzyme nanoelectrodes have been constructed by immobilizing glucose oxidase, alcohol oxidase or tyrosinase onto ultrathin carbon films (of 35–50 nm thickness). The enzyme immobilization is accomplished via entrapment within electropolymerized poly(o-phenylenediamine) coatings. Cyclic voltammetry and controlled-potential amperometry are used to characterize the performance of the new nanoscopic biosensors under different preparation and operation conditions. The resulting electrodes offer convenient and rapid measurements of millimolar substrate concentrations, and (to the best of our knowledge) are the smallest enzyme probes reported to date.

ISSN:0003-2719    

DOI:10.1080/00032719308017416

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

S-layer ultrafiltration membranes (SUMs) with an active filtration layer composed of coherent two-dimensional, isoporous protein crystals (S-layers) have been used as matrix for immobilizing monolayers of enzymes. Since S-layers are formed by periodic repetition of identical protein subunits, functional groups are present on the crystalline array in an identical position and orientation. As a consequence monolayers of enzymes can bind in a geometrically well defined way. For the covalent immobilization of enzymes carboxyl groups from the S-layer protein were activated with carbodiimide and allowed to react with amino groups of the enzyme. SUMs were employed as a new type of immobilization matrix for the developement of an amperometric glucose sensor using glucose oxidase (GOD) as the biologically active component. Glucose oxidase covalently bound to the surface of the S-layer protein retained approximately 40% of its activity. The enzyme loaded SUMs were covered with a layer of gold or platinum to function as working electrodes. These sensors yielded high signals (150nA/mm2/mmol glucose), fast response times (10–30s) and a linearity range up to 12 mM glucose. The stability under working conditions was more than 48 hours. There was no loss in activity after a storage period of 6 month.

ISSN:0003-2719    

DOI:10.1080/00032719308017417

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The electrochemical behavior and detection of some molecules of biological significance were studied. The separation and detection of some neurotransmitters, namely, norepinephrine, L-DOPA, epinephrine, and dopamine were accomplished using reverse phase high performance liquid chromatography(HPLC) and amperometric detection, respectively. The voltammetric behavior of these molecules was compared using different polymeric electrodes. Electrocatalytic “efficiency” decreases in the order of poly(3-methylthiophene)(P3MT), poly(N-methylpyrrole)(PNMP), poly(aniline)(PAn) and poly(furan)(PF). P3MT showed improved performance as an amperometric detector for HPLC analysis systems over other types of polymer and conventional electrodes examined. Detection limits as low as 10−8-10−9M were achieved using the P3MT, compared to 10−6-10−8M using glassy carbon or platinum electrodes. The nature of the substrate used for the polymer deposition had no effect on the electrochemical characteristics of the compounds studied. The results describes the intrinsic catalytic property of the polymer electrode surface towards the redox behavior of the compounds studied. The polymer electrode showed promising antifouling resistant against common fouling agents.

ISSN:0003-2719    

DOI:10.1080/00032719308017418

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Dichlorophenolindophenol (DCPIP) was electrochemically deposited onto the surface of glassy carbon and platinum electrodes to form a permselective film. Cyclic voltammetry of the DCPIP coated electrode exhibited a reversible oxidation/reduction current at +0.14 V, behavior similar to monomeric DCPIP. However, such an electrode did not mediate glucose oxidase in the presence of β-D-glucose. For operation at +0.7 V vs Ag/AgCl, the DCPIP electrodeposited film behaved like a permselective membrane and virtually eliminated oxidative interference currents resulting from 0.2 mM acetaminophen, uric acid and glutathione. For ascorbic acid, interfering current due to 0.2 mM ascorbate was decreased by 80%. Improvement of the selectivity due to ascorbic acid was achieved using an electrodeposited film prepared from a mixture of DCPIP with diaminobenzene or resorcinol.

ISSN:0003-2719    

DOI:10.1080/00032719308017419

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A simple formula is proposed for the definition and the calculation of the highest acceptable selectivity coefficient values of ion-selective electrodes. On the basis of the formula which is based on the consideration of the precision of the direct potentiometric measuring techniques one can easily decide whether the selectivity of an electrode is sufficient or not for solving a well defined analytical task correctly. On the other, hand it indicates clearly for ion-selective electrode developing teams or manufacturers how far the ion-selectivity of an electrode should be improved for a certain type of analytical application.

ISSN:0003-2719    

DOI:10.1080/00032719308017420

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Silicon nitride membrane ISFET sensor chips have been produced with varying gate dimensions. A series of width/length (W/L) aspect ratios have been examined, combined with three levels of boron ion-implant. The level of ion-implantation affects the threshold voltage; this is important as a low threshold voltage allows the use of low noise operating conditions. Gate dimensions are also important factors for they determine the level of drain current for a given gate and drain voltages. A novel design feature, aimed at achieving wide gates, is the use of folded gates as well as having a straight structure. The evaluation of devices with gates covered with poly(vinyl chloride) (PVC)-valinomycin-dioctyl adipate was based on their response to potassium chloride standards when it was shown that there may be a maximum width of gate above which there is no improvement of response. Also, the effect of folding the gate structure is discussed and shown to be tenable, thus permitting greater miniaturisation.

ISSN:0003-2719    

DOI:10.1080/00032719308017421

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor