Catalase sensors

Based on these chemosensors, biosensors can be set up such as glucose or H2O2 sensors. In this case the appropriate biological compound (glucose oxidase or catalase) must be immobilized on the chemosensor. Different optical sensors are also used as transducer elements for the production of biosensors, especially of immuno-sensors. Here the affinity component is immobilized on the tip of the fiber and all available immuno-sensing assays can be performed using this transducer element. Since these sensors cannot be sterilized and used for on-line monitoring in a bioprocess we refer to other publications [25-27]. 

Matsumoto et al (41) prepared a multi-enzyme electrode using glucose oxidase, invertase, mutarotase, fructose-5-dehydrogenase, and catalase to simultaneously detect glucose, fructose, and sucrose in fruit juices and soft drinks. Detection of multi-components by enzyme sensors was also reported in analysis of sucrose and glucose in honey (42) and drinks (43), and L-malate and L-lactate in wines (44). 

There are two major problems encountered with this approach. First is the selfinhibition caused by the hydrogen peroxide this has been mentioned before. It is less acute in this case than in the hydrogen peroxide sensor because the catalase substantially eliminates any excess of H2O2. The second problem is encountered when the electrode is used in vivo. The tissue or blood concentration of oxygen, which is the cosubstrate, is low and at high glucose concentrations the current becomes limited by the availability of oxygen. 

For this type of sensor, a catalase-free glucose oxidase must be used. In such a case, the hydrogen peroxide produced by the reaction with oxygen remains in the selective layer and can be detected by oxidation according to the reaction... 

Physicochemical fundamentals of construction and action of catalase- and peroxidase-biomimetic sensors are studied. 

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. 

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. 

The investigations of catalase-mimetic sensors allow continuation of studies in the field of biomimetic sensors of peroxidase type. 

Ag reaction with catalase-labeled antigen. After competitive binding of free and catalase-labeled AFP, the sensor is examined for catalase activity by ampero-metric measurement after addition of H 2O2. AFP can be assayed in the rjuige 10-0.01 ng/mL. 

The system has been improved through redesigning the closed-flow microdialysis perfusion system of the sensor to minimize the risk of enzyme leakage by immobilizing the enzymes GOD and catalase in an enzyme reactor. 

The reaction of peroxide with ferrous heme iron is the basis of electrocatalytic peroxide sensors. A selection that gives a representative overview of the biomolecules and transducers is included in Table 2.5. Peroxidase, catalase, haemoglobin, cytochrome c, microperoxidase and hemin can all be explored for peroxide measurement. Most papers on DET-based biosensor are related to peroxide detection in a variety of environments with peroxidases. 

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