Enzyme-based biosensor with amperometric detection

Enzyme-Based Biosensors with Amperometric Detection... 

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. 

The potential for the coexistence of several enzymes in tissue materials can also be a major drawback as it can affect the selectivity of the device when used in complex sample media. Some of the strategies that have been employed for improving the selectivity of tissue-based biosensors include the use of activators to promote the primary reaction, inhibitors to suppress the undesirable reactions, or preincubation of the desired substrate. Under favorable conditions, the multienzyme activity of the tissue can be exploited for the detection of multicomponents in real samples. For example, with amperometric detection, such multicomponent detection may require the application of different potentials to achieve improved selectivity. 

Enzyme-based biosensors have been used also for the detection of phenolic estrogens. The detection principle was based on the ability of tyrosinase to catalyze the oxidation of phenolic estrogens to o-diphenol and o-quinone. Using this principle tyrosinase-carbon paste electrodes have been used for the detection of phenol, catechol, bisphenol A, genistein, quercetin, nonylphenol, and diethylstilbestrol with detection levels in the micromolar range.Optical and amperometric biosensors based on estrogen receptors have also been developed. 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

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