Glucose oxidation electrodes

Figure 17.11 Schematic representation of an approach for achieving efficient electrocatalysis of glucose oxidation by glucose dehydrogenase on Au nanoparticles tethered on an Au electrode. The nanoparticles are modified with a PQQ-capped linker that interacts with the unoccupied PQQ site of cofactor-deficient glucose dehydrogenase [Zayats et al., 2005].

The first enzyme biosensor was a glucose sensor reported by Clark in 1962 [194], This biosensor measured the product of glucose oxidation by GOD using an electrode which was a remarkable achievement even though the enzyme was not immobilized on the electrode. Updark and Hicks have developed an improved enzyme sensor using enzyme immobilization [194], The sensor combined the membrane-immobilized GOD with an oxygen electrode, and oxygen measurements were carried out before and after the enzyme reaction. Their report showed the importance of biomaterial immobilization to enhance the stability of a biosensor. 

Oxygen, which is consumed by the primary glucose oxidation, is regenerated by the oxidation of hydrogen peroxide at the surface of the electrode. Moreover, because the operating potential is positive, oxygen is not consumed at the electrode. Therefore, the reaction is not limited by the concentration of oxygen for which the boundary conditions are... 

The increased sensitivity of the electrodes coated with the hydrophobin layer is also appealing. The hydrophobin-modified electrodes allow H2O2, the product of glucose oxidation, to be detected at a concentration of 0.2 mM. This level is significantly lower than the detection limit of the bare electrode, which is 0.9 mM. The authors attribute the increase in electrode performance to the local accumulation of H202 at the electrode surface or a possible decrease in current in the presence of the hydrophobin layer. 

Carbonaceous substrates (graphite and glassy carbon) are generally preferred because of their mechanical, chemical, and electrochemical properties. Excellent results are also obtained by chemically modified platinum (154,156,179) and tin(IV) oxide electrodes (155). For example, glucose oxidase has been successfully immobilized by cross-linking the enzyme with BSA and GA onto an electrochemically oxidized platinum surface, with silanization using 3-amino-propyltriethoxysilane ... 

Association between enzymatic and electrochemical reactions has provided efficient tools not only for analytical but also for synthetic purposes. In the latter field, the possibilities of enzymatic electrocatalysis, e.g., the coupling of glucose oxidation (catalyzed either by glucose oxidase or glucose dehydrogenase) to the electrochemical regeneration of a co-substrate (benzoquinone or NAD+) have been demonstrated [171, 172]. An electroenzymatic reactor has also been developed ]172] to demonstrate how the enzyme-electrode association can be used to produce biochemicals on a laboratory scale. 

Some details are given by Merck in Ref. 112. The electrochemical oxidation is performed in alkaline solution using nickel or nickel oxide electrodes [113]. Hydrogen evolved at the cathode can be used for the hydrogenation of D-glucose to D-sorbitol, the first step in the vitamin C synthesis by the Reichstein route. Obviously, Merck doesn t use electrodes with high specific areas but prefers to stop the electrolysis at a conversion rate of 90%. The oxidation is completed with sodium hypochlorite solution. 

Gorton, L, Bremle, G., Gsoregi, E., Jdnsson-Pettersson, G., and Persson, B. (1991) Amperometric glucose sensors based on immobilized glucose-oxidizing enzymes and chemically modified electrodes. Analytica Chimica Acta, 249, 43-54. 

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