Catalase-biomimetic electrode

Figure 8.8 Apparent mechanism of catalase-biomimetic electrode operation in electrocatalytic mode.

Figure 8.2 shows an electrochemical system - a model of a catalase-biomimetic sensor, consisting of the reference electrode (Ag/AlCl/Cl ) and biomimetic electrode. In this system, the electrochemical potential changed as a result of mimetic electrode interaction with... 

The change of electrode potential (E) of the catalase reaction with time was measured by a voltmeter. pH and E values for aqueous hydrogen peroxide were determined simultaneously for possible correlations between pH metric and potentiometric results of enzymatic activity of catalase-biomimetic sensors. The electrochemical unit was also equipped with a magnetic mixer. 

For the purpose of determining low hydrogen peroxide concentrations, the authors have designed the most cost-effective and simple to use potentiometric-biomimetic sensors based on immobilized catalase mimics. These sensors possess high hydrodynamic properties and the fastest speed of response. Figure 8.3 shows experimental data on catalase activity of biomimetic electrode in 0.03% aqueous H202. For the sake of comparison, catalase activities of aluminum electrode and aluminum electrode with applied adhesive are also shown. 

It is common knowledge that hydrogen peroxide is a soft dibasic acid. Therefore, catalase activity of biomimetic electrodes may change the pH of the H202 solution by both... 

A definite quantity of oxygen molecules accumulated on the surface of the biomimetic electrode (catalase reaction) must diffuse to the volume of the adhesive layer, toward the electrode surface. Hence, the specific requirements to the adhesive follow on the one hand, it must provide strong enough adhesion of a mimic to electrode on the other hand, it must possess low oxygen adsorption ability. 

Thus, two reactions (catalase and electrochemical) are implemented in the biomimetic electrode-H202-Cr-AgCl-Ag system. In the case of inorganic support, it is not the kinetic but the diffusion (external and internal) factor that is predominant, owing to which the electrochemical reaction is of a self-oscillation type [7, 8],... 

By analogy with the mechanism of the catalase reaction, the probable mechanism of the peroxidase reaction is considered (Figure 8.12). Note that a proton transferred to the active site of the biomimetic electrode can be replaced by H+ from the reaction mixture volume. The mechanisms of catalase and peroxidase reactions provide an insight into the ways of their realization in the electrochemical mode. The ratio of products synthesized in both reactions (02 and CH3CHO) depends on the ratio of the H202 and CH3CHO interaction rates with the surface intermediate. 

Biomimetic sensors, prepared from catalase adsorbed on diasorb and A1203, treated with trypsine and adhered to an aluminum electrode surface using 7.5% polyacrylamide gel of... 

Biomimetic sensors, prepared by catalase adsorption on diasorb and agarose (treated with trypsine) and adhered to an aluminum electrode surface by Pattex adhesive, displayed an abrupt decrease of the electrode potential. Sensors prepared by catalase adsorption on A1203 (without trypsine treatment) and adhesion to the aluminum electrode with Pattex adhesive displayed a high oscillation of the electrode potential, which induces extreme instability of the operation. Hence, it should be noted that sensor operation was always better in the case of enzyme treatment with trypsine. 

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