Enzyme electrodes galactose

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... 

Chemically binding enzymes to nylon net is very simple and gives strong mechanically resistant membranes (135). The nylon net is first activated by methylation and then quickly treated with lysine. Finally, the enzyme is chemically bound with GA. The immobilized disks are fixed direcdy to the sensor surface or stored in a phosphate buffer. GOD, ascorbate oxidase, cholesterol oxidase, galactose oxidase, urease, alcohol oxidase (135), and lactate oxidase (142) have been immobilized by this procedure and the respective enzyme electrode performance has been established. 

Between 15 and 20 analyzers based on enzyme electrodes are on the market worldwide. They are one-parameter instruments for the measurement of glucose, galactose, uric add, choline, ethanol, lysine, lactate, pesti-ddes, sucrose, lactose, and the activity of a-amylase (Table 23). They provide for a negligible enzyme consumption of less than 1 pg per sample. 

Other examples of amperometric enzyme electrodes based on the measurement of oxygen or hydrogen peroxide include electrodes for the measurement of galactose in blood (galactose oxidase,enzyme), oxalate in urine (oxalate oxidase), and cholesterol in blood serum (cholesterol oxidase). Ethanol is determined by reacting with a cofactor, nicotinamide adenine dinucleotide (NAD" ) in the presence of the enzyme alcohol dehydrogenase to produce the reduced form of NAD", NADH, which is electrochemically oxidized. Lactate in blood is similarly determined (lactate dehydrogenase enzyme). 

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. 

Galactose is determined by immobilizing the enzyme galactose oxidase at an oxygen electrode (190) or at a micro-platinum electrode operating anodically to monitor H2O2 formation (191, 192). The enzyme is immobilized on collagen membranes (193) or cellulose acetate membranes, and the probe is applied selectively to plasma d whole blood determinations (191, 194). 

In addition to a family of SODs, several other kinds of enzymes and proteins, including tyrosinase [87], galactose oxidase [87], hemin, and cytochrome c (Cyt. c), have been employed to construct enzyme-based biosensors for the O2 determination. Here, we will use Cyt. c as an example to illustrate the analytical mechanism of such a kind of 02 biosensors. For constructing a Cyt. c-based biosensor, Cyt. c is normally inunobilized on the electrode surface and acts as an electron transfer mediator between the electrode and 02. The O2 radical reduces the immobilized Cyt. c (Fe(lll)) to Cyt. c (Fe(II)) and the Cyt. c (Fe(ll)) is reoxidized on the electrode at a potential of... 

A qiiantitative assay for D-galactose depends on an enzyme sensor based on d-galactose oxidase and a tris(2,2 -bipyridine) complex of osmium as a redox mediator developed on a carbon electrode. ... 

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