Glucose oxidase, adsorption

FIGURE 1.19 Schematic representation of glucose oxidase adsorption, (a) Situation where the potential is positive with respect to the zero potential value (b) case where the potential is equal to that of zero charge and (c) final state where the enzyme is unfolded. 

A colloidal suspension of conductive vanadium pentoxide [130] can be used to perform intercalation, adsorption or encapsulation of electroactive molecules or biomolecules for electrodes or biosensor realization [131]. Encapsulation of glucose oxidase in nanocomposite films made with polyvinyl alcohol and V205 sol-gel matrix or in ferrocene intercalated V2Os sol-gel [132] were envisaged to prepare glucose biosensors. 

H. Tang, J. Chen, S. Yao, L. Nie, G. Deng, and Y. Kuang, Amperometric glucose biosensor based on adsorption of glucose oxidase at platinum nanoparticle-modified carbon nanotube electrode. Anal. Biochem. 331, 89-97 (2004). 

Ikariyama [2] described a unique method for the preparation of a glucose oxidase (GOD) electrode in their work. The method is based on two electrochemical processes, i.e. electrochemical adsorption of GOD molecules and electrochemical growth of porous electrode. GOD immobilized in the growing matrix of platinum black particles is employed for the microfabrication of the enzyme electrode. It demonstrated high performance with high sensitivity and fast responsiveness. 

Glucose oxidase was first adsorbed onto the platinum surface at a controlled potential. The protein adsorption varied depending on several factors as electrode potential, glucose oxidase concentration, pH and temperature. The effects of these factors on protein adsorption were carefully investigated. 

In a system devised to oxidize a dye, glucose oxidase and horseradish peroxidase were coassembled by layer-by-layer alternative adsorption to construct multienzyme films. The peroxidase was adsorbed to poly(styrene sulfonate) while glucose oxidase was adsorbed to poly(ethylene imine), allowing for sequential redox reactions to take place resulting in the subsequent oxidation of the textile dye DA67 [71]. 

Polyelectrolyte multilayer microspheres, prepared by alternating adsorption of dextran sulfate and protamine on melamine formaldehyde cores followed by the partial decomposition of the core, were used to immobilise the peroxidase and glucose oxidase. Retention of enzymic activity of the peroxidase/glucose oxidase system incorporated into the microspheres was demonstrated. These bienzyme system immobilised in the microspheres can be applied for kinetic glucose assays [ 156]. 

Electron-Mediated Biosensor. Electropolymerization of 1,3-diaminobenzene (1,3-DAB), followed by adsorption of l,r-dimethylferrocene (1,1 -DMF), and immobilization of glucose oxidase, results in an easily and quickly (<2 h) constructed glucose biosensor with excellent linearity and stability (>3 months). Figure 5 shows a proposed schematic of the sensing layer consisting of film/mediator/enzyme. The ferrocene is depicted as circles... 

The hydrophobias are a case where protein nanofibers can play a dual role in creating a biosensor. They can aid in the immobilization of bioactive components within a biosensor and also add further functionality to the transducing element of a biosensor device. Hydrophobins are self-assembling [3-sheet structures observed on the hyphae of filamentous fungi. They are surface active and aid the adhesion of hyphae to hydrophobic surfaces (Corvis et al., 2005). These properties can be used to create hydrophobia layers on glass electrodes. These layers can then facilitate the adsorption of two model enzymes glucose oxidase (GOX) and hydrogen peroxidase (HRP) to the electrode surface. The hydrophobin layer also enhances the electrochemical properties of the electrodes. 

Fig. 14.20. Schematic representation of the adsorption process of glucose oxidase (GO) (a) The potential is much more positive than the potential of zero charge, (b) The potential is close to the pzc. (c) The final stage when the enzyme unfolded. (Reprinted from A. Szucs, G. D. Hitchens and J. O M. Bockris, J. Electrochem. Soc. 136(12) 3748, Fig. 13, 1989. Reproduced by permission of the Electrochemical Society, Inc.)...

A recent successful approach uses mediators like ferrocene, which reoxidizes the FADH 2 in the glucose oxidase molecule without forming hydrogen peroxide (85). Using ferrocene results in a more stable electrode system and a larger dynamic concentration range. The ferrocene molecule is immobilized by adsorption to graphite or other carbon electrodes onto which the enzyme can be deposited. 

M. Onda, Y. Lvov, K. Ariga, T. Kimitake, Sequential Actions of Glucose Oxidase and Peroxidase in Molecular Films Assembled hy Layer-hy-Layer Alternate Adsorption , Biotech. Bioeng., 51, 163 (1996)... 

A layer-by-layer alternate electrostatic adsorption of monolayers of a positively-charged dendrimer (G4 poly(amidoamine)) and the negatively-charged protein glucose oxidase allows the preparation of multilayered assemblies for the construction of amperometric glucose sensors. This multilayer... 

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