Electrochemical sensors enzyme

Electrochemical sensors enzyme electrodes and held effect transistors... 

Electrochemical sensor Enzyme Metabolite Measurement range (mmol 1 )... 

Immobilized Enzymes. The immobilized enzyme electrode is the most common immobilized biopolymer sensor, consisting of a thin layer of enzyme immobilized on the surface of an electrochemical sensor as shown in Figure 6. The enzyme catalyzes a reaction that converts the target substrate into a product that is detected electrochemicaHy. The advantages of immobilized enzyme electrodes include minimal pretreatment of the sample matrix, small sample volume, and the recovery of the enzyme for repeated use (49). Several reviews and books have been pubHshed on immobilized enzyme electrodes (50—52). 

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors (qv) require multiple steps for analyte determination, and either sandwich assays or competitive binding assays maybe used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. In the sandwich assay type, the membrane-bound antibody binds the sample antigen, which in turn binds another antibody that is enzyme-labeled. This immunosensor is then placed in a solution containing the substrate for the labeling enzyme and the rate of product formation is measured electrochemically. The rate of the reaction is proportional to the amount of bound enzyme and thus to the amount of the analyte antigen. The sandwich assay can be used only with antigens capable of binding two different antibodies simultaneously (53). 

L-lactate-cytochrome c-oxidoreductase (flavocytochrome was isolated for the first time from the thermo-tolerant yeast H. polymorpha. The mentioned above enzyme preparations were used for construction of the biorecognition elements of electrochemical sensors. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

The high specificity required for the analysis of physiological fluids often necessitates the incorporation of permselective membranes between the sample and the sensor. A typical configuration is presented in Fig. 7, where the membrane system comprises three distinct layers. The outer membrane. A, which encounters the sample solution is indicated by the dashed lines. It most commonly serves to eliminate high molecular weight interferences, such as other enzymes and proteins. The substrate, S, and other small molecules are allowed to enter the enzyme layer, B, which typically consist of a gelatinous material or a porous solid support. The immobilized enzyme catalyzes the conversion of substrate, S, to product, P. The substrate, product or a cofactor may be the species detected electrochemically. In many cases the electrochemical sensor may be prone to interferences and a permselective membrane, C, is required. The response time and sensitivity of the enzyme electrode will depend on the rate of permeation through layers A, B and C the kinetics of enzymatic conversion as well as the charac-... 

If the electrochemical sensor does not require a permselective membrane, immobilization of the enzyme onto the surface of the electrode is possible. Glassy carbon graphite reticulated vitreous carbon and carbon paste electrodes... 

Based on many of the advances described above in electrochemical approaches to immunoassay, it is tempting to conclude that commercialization of some of the approaches is imminent. This may be true, but the historical use of optical methods for many clinical chemistry tests coupled with their rapidly growing use in immunoassay is a difficult barrier for any radically different method to overcome, though electrochemical sensors have become more important in the clinical chemistry laboratory over the last decade. In any event, to be successful ECIA methods will have to demonstrate clear superiority over existing and emerging technologies in both cost and performance. Some of the more recently described approaches such as those using enzyme amplified amperometric detection and ecLIA appear... 

The first interest in the electroreduction of N02 or NO catalyzed by metal complexes is to model the activity of nitrite reductase enzymes.327 There is also an extensive growth in studies related to the development of metal complex-based electrochemical sensors for NO determination in biological and environmental samples 328 329 Nitrate disproportionates to nitric oxide and nitrate in aqueous solution. 

C.J. Mcneil, D. Athey, M. Ball, W.O. Ho, S. Krause, R.D. Armstrong, J.D. Wright, and K. Rawson, Electrochemical sensors based on impedance measurement of enzyme-catalyzed polymer dissolution theory and applications. Anal. Chem. 67, 3928-3935 (1995). 

Though less commonplace, there are some electrochemical sensors based on integrated dialysis, reaction and detection. Most of them use a retained enzyme immobilized in a microcavity at the tip of the working electrode that... 

Electrochemical biosensors [18] Here we mean biomimetic sensors, which utilize the ability of biological materials (enzymes, antibodies, etc.) to recognize specific components and to catalyze their reactions with great specificity. Many of the biosensors are electrochemical sensors, based on potentio-metric or amperometric measurements. For example, in the case of an amperometric... 

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors require multiple steps for analyte determination, and either sandwich assays or competitive binding assays may be used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. 

The most obvious way to incorporate this chemistry into an electrochemical sensor is to immobilize the enzyme onto an electrode surface and use this electrode to oxidize the hydrogen peroxide produced. An enzymatic sensor of this type was first prepared by Guilbault and Lubrano [91]. Numerous variations on this theme have since appeared, and sensors that employ this electrochemistry are now commercially available. 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

There are problems with this approach since enzymes isolated from natural sources such as the electric organ of electric eels often display low sensitivity and selectivity to the wide range of potential pesticide targets [21]. A possible solution to this is the development of a multisensor array where a variety of genetically modified acetylcholinesterases are immobilised on an array of electrochemical sensors and the responses from these are then processed via a neural network. 

Vegetable tissue based electrochemical sensors can be divided into two groups according to their principle of operation potentiometric and amperometric. Such devices are usually prepared in a manner similar to that of conventional enzyme electrodes, with the detection of an electroactive species that is consumed or produced by the enzyme present in the vegetable tissue. 

S. J. Setford, S.F. White and J.A. Bolbot, Measurement of protein using an electrochemical bi-enzyme sensor, Biosens. Bioelectron., 17 (2002) 79-86. P. Sarkar and A.P.F. Turner, Application of dual-step potential on single screen-printed modified carbon paste electrodes for detection of amino acids and proteins, Fresenius J. Anal. Chem., 364 (1999) 154-159. 

Screen-printed enzyme-free electrochemical sensors for clinical and food analysis... 

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