Bienzyme biosensors

Scheme 9. Principle of action a bienzyme biosensor incorporating HRP, an oxidase (Efad), and a an electron shuttle.

S. Campuzano, M. Pedrero, F.J. Manuel de Villena and J.M. Pingarron, A lactulose bienzyme biosensor based on self-assembled monolayer modified electrodes, Electroanalysis, 16(17) (2004) 1385-1392. 

R. Dominguez, B. Serra, A.J. Reviejo and J.M. Pingarron, Chiral analysis of amino acids using electrochemical composite bienzyme biosensors, Anal. Biochem., 298(2) (2001) 275-282. 

Mediators such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) [166], hexacyanoferrate(III) [168] and CoPC [169], which have been applied to a carbon paste or ink, are reduced by the reaction with thiocholine and then reoxidised at the carbon electrode (Fig. 23.6). A second type of mediator has involved the addition of Prussian blue (ferric hex-anocyanoferrate) into an AChE and choline oxidase (ChO) bienzyme biosensor. Prussian blue mediates the reduction of hydrogen peroxide produced by the conversion of choline to betaine by ChO [170]. 

The primary objective of ChE-ChOx bienzyme biosensors was to determine neurotransmitter acetylcholine in biological samples (Chen et al, 1998). The redox potential of acetylcholine (ACh) is too high to be determined directly using electrochemical reaction. For this purpose, acetylcholine esterase (AChE) was employed as ChE. AChE and ChOx were immobilized on the surface of the electrode to attain electrochemical analysis according to reactions (4) and (5) (Scheme 55.3). 

The enzymatic reactions of AChE-ChOx bienzyme biosensor consist of AChE-catalyzed hydrolysis of ACh into choline and acetic acid [reaction (4)] and oxidation reaction... 

TABLE 55.1. AChE-ChOx bienzyme biosensors for detecting OP compounds... 

FIGURE 57.13. Molecular architecture of bienzyme biosensor electrode containing tyrosinase and neuropathy target esterase catalytic domain (NEST). Reproduced with permission from Kohli et al. (2007a). 

Another technique to increase the dispersability and the biocompatibility of the carbon nanotubes is the insertion of terminal groups on the surface of CNTs with a procedure called functionalization [104, 105, 118, 123, 136]. The creation of free carboxylic acid and amino acid moieties on the surface are the most commonly used functionalization for enzyme immobilization and stabilization [104, 105, 118,123, 136]. Apart from these two functional groups, other groups are also used, for various purposes. For example, Jeykumari and Narayanan functionalized MWCNTs with toluidine blue, in order to prevent the leakage of the redox mediator from their bienzymic biosensor [114]. 

Aseris, V., R. Baronas, and J. Knlys. 2013. Computational Modeling of Bienzyme Biosensor with Different Initial and Boundary Conditions. Informatica 24 (4) 505-521. 

The enzymatic reactions of AChE-ChOx bienzyme biosensor consist of AChE-catalyzed hydrolysis of ACh into choline and acetic acid (reaction (4)) and oxidation reaction of choline catalyzed by ChOx (reaction (5)). The latter reaction produces H2O2, which can be electrochemically oxidized on tire electrode to generate output signal depending on tire concentration of AChE. It is also possible to use an oxygen electrode in place of a metal or carbon electrode because ChOx consumes dissolved O2 during the oxidation of choline. Therefore,... 

TABLE 62.1 AChE-ChOx Bienzyme Biosensors for Detecting OP Compounds... 

Li, F., Wang, Z., and Feng, Y. (2009) Construction of bienzyme biosensors based on combination of the one-step electrodeposition and covalent-coupled sol-gel process. Sci. China Ser. B, 52, 2269-2274. 

This idea of coupling the two laccase and tyrosinase enzymes has been repeatedly used in the literature by different authors. For example, a tyrosinase/laccase bienzyme biosensor for amperometric determination of phenolic compounds was constructed by immobilizing enzymes in titania gel matrix. The obtained biosensor could be used for determination of 2,6-dimethoxyphenol, 4-tertbutylcatechol,... 

Kochana J, Nowak P, Jarosz-Wilkolazka A, Bieron M (2008) Tyrosinase/laccase bienzyme biosensor for amperometric determination of phenolic compounds. Microchem J 89 (2) 171-174... 

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