Enzyme electrodes amino acids

G.G. Guilbault and G.J. Lubrano, Amperometric enzyme electrodes. Amino acid oxidase. Anal. Chim. Acta 69, 183-185 (1974). 

Based on the work of Clark and Lyons [176] as well as Hicks and Updike [177], Guilbault and Montalvo [178-181] immobilized the enzyme. They coated a traditional cation-selective glass electrode (responding to NH4) with the enzyme (urease, amino-acid oxidase) in a polymerized acrylamide gel matrix. For better mechanical stability, the gel was reinforced with a nylon net or a cellophane foil. The enzymes reacted specifically only with the urea and amino acids, respectively, in the solution to produce NH4 ions, which were indicated by the cation-selective electrode. This electrode construction functioned as a specific detector for over three weeks with no loss in activity. The urea sensor spanned a concentration range of 1.6 x 10" to 5 x 10" M with a response time of only approximately 25 seconds. 

Although the primary focus of oxidase based enzyme electrodes has been the determination of glucose, the list of extensions to other analytes is considerable. Systems have been described for cholesterol 123,132-136) galactose ii -i35-i37) dd i38.i39) lactatepyruvatecreatinine serum lipaseethanoland amino acids... 

Enzyme electrodes for the amino acids tyrosine and lysine have been... 

There are also RMs which are prepared for a specific application and are used for validation of relevant methods. Cobbaert et al. (1999) made use of Ion Selective Electrode (ISE)-protein-based materials when evaluating a procedure which used an electrode with an enzyme-linked biosensor to determine glucose and lactate in blood. Chance et al. (1999) are involved with the diagnosis of inherited disorders in newborn children and they prepared a series of reference materials consisting of blood spotted onto filter paper and dried, from which amino-acids can be eluted and... 

Covalent chemical attachment of an enzyme to an electrode or a polymer coating requires mild and specific chemistry to react with amino acids in the protein in aqueous... 

Fortier [6] found that AQ polymer from Eastman was not deleterious for the activity of a variety of enzymes such as L-amino acid oxidase, choline oxidase, galactose oxidase, and GOD. Following mixing of the enzyme with the AQ polymer, the mixture was cast and dried onto the surface of a platinum electrode. The film was then coated with a thin layer of Nafion to avoid dissolution of the AQ polymer film in the aqueous solution when the electrode was used as a biosensor. These easy-to-make amperometric biosensors, which were based on the amperometric detection of H202, showed high catalytic activity. 

Potentiometric enzyme-based electrodes have found application in clinical, pharmaceutical, food and biochemical analyses to enable the selective determination of a wide range of important enzyme substrates, including amino acids, esters, amides, acylcholines, /Mactam antibiotics, sugars, enantioselective drugs and many others [74]. 

Amperometric biosensors incorporating certain enzymes on the electrode for the determination of D- and L-amino acids were investigated. The parameters included enzyme immobilization procedure, composition of the immobilizing matrix, amount of enzyme,... 

An unusual type of derivative is the complex that forms between urease and bentonite in acid medium (61). The adsorbed form was found catalytically active. Similarly, urease immobilized in a polyacrylamide gel matrix has been used to prepare a urea-specific enzyme electrode (62). Yet another active water-insoluble derivative has been prepared (63) by allowing p-chloromercuribenzoate-treated urease to react with a diazotized copolymer of p-amino-D,L-Phe and L-Leu. Urease has been found to retain about 20% of its original activity when encapsulated in 100 n microcapsules of benzalkonium-heparin in collodion (64). 

Another approach to dealing with the nonelectrochemically active nature of most amino acids is to generate, in situ, chemical reactions at the electrode surfaces to produce electrochem-ically active products for detection. Related to this concept, is the online use of immobilized enzymes (142) to react with amino acids. A by-product of this reaction is hydrogen peroxide, which is then quantified by amperometric detection. 

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. 

Construction principles and the mechanism for biosensors derived from enzymes. Combined enzymatic and electrochemical reactions proceeding on electrodes from various materials in electrolyte solutions promote development of many biosensor types for detection of glucose, amino acids, lactose, urea, pyruvate and other metabolites. Biosensors are successfully applied to environmental contamination control, medical diagnostics and the food industry. 

Aspartame has been assayed by a flow injection analysis biosensor employing an immobilized enzyme (pronase) which cleaves the peptide bond. The resulting phenylalanine methyl ester is then detected by an L-amino acid oxidase electrode. This method was applied to analysis of aspartame in foods [82]. 

A sensitized electrode is a composite device that combines a membrane reactor and a primary electrode. The membrane reactor converts a specific analyte into products that are measurable by the primary electrode. Membrane reactors containing immobilized enzymes, cells, or neutral carriers are capable of very selective conversion of sugars, amino acids, organic acids, and alcohols, and... 

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