Glucose oxidase cyclic voltammetry

Electron transfer of the glucose oxidase/polypyrrole on the electrode surface was confirmed by differential pulse voltammetiy and cyclic voltammetry. The glucose oxidase clearly exhibited both reductive and oxidative current peaks in the absence of dissolved oxygen in these voltammograms. These results indicate that electron transfer takes place from the electrode to the oxidized form of glucose oxidase and the reduced form is oxidized by electron transfer to the electrode through polypyrrole. It may be concluded that polypyrrole works as a molecular wire between the adsorbed glucose oxidase and the platinum electrode. 

Plasma polymerized N-vinyl-2-pyrrolidone films were deposited onto a poly(etherurethaneurea). Active sites for the immobilization were obtained via reduction with sodium borohydride followed by activation with l-cyano-4-dimethyl-aminopyridinium tetrafluoroborate. A colorometric activity determination indicated that 2.4 cm2 of modified poly(etherurethaneurea) film had an activity approximately equal to that of 13.4 nM glucose oxidase in 50 mM sodium acetate with a specific activity of 32.0 U/mg at pH 5.1 and room temperature. Using cyclic voltammetry of gold in thin-layer electrochemical cells, the specific activity of 13.4 nM glucose oxidase in 0.2 M aqueous sodium phosphate, pH 5.2, was calculated to be 4.34 U/mg at room temperature. Under the same experimental conditions, qualitative detection of the activity of a modified film was demonstrated by placing it inside the thin-layer cell. 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

Fig. 1 Cyclic voltammetry of the catalysis of the electrochemical oxidation of / -D-glucose by glucose oxidase with ferrocene methanol as the cosubstrate. Dashed line ferrocene methanol (0.1 M) alone the same trace is obtained in the presence of glucose oxidase (27 pM) with no glucose present or in the presence of glucose (0.5 M) with no gl ucose oxidase present. Dotted and full lines ferrocene methanoi (0.1 mM) + giucose oxidase(27 pM) + glucose (0.5 M) at pH 4.5 (acetate buffer) and 6.5 (phosphate buffer), respectively. Ionic strength 0.1 M. Scan rate ...

Fig. 6 Cyclic voltammetric analysis of the kinetics of an electrode coated with antigen-antibody immobilized monomolecular layer of redox enzyme with a one-electron reversible cosubstrate in the solution, (a) Cyclic voltammetry at saturation coverage (2.6 x 10 mol cm ) of glucose oxidase with 0.1 M glucose and 0.1 mM ferrocenemethanol in a pH 8 phosphate buffer (0.1 M ionic strength). The dotted and dashed lines represent the cyclic voltammogram (0.04 V sec ) in the absence and presence of glucose (0.1 M), respectively. The full line represents the catalytic contribution to the current,/ cat (see text), (b) Primary plots obtained under the same conditions with, from top to bottom, 0.01, 0.02, 0.05, and 0.1 M glucose, (c) Secondary plot derived from the intercepts of the primary plots in (b).

Fig. 14 Cyclic voltammetry of glucose oxidase coated glassy carbon electrodes with an increasing number (N) of monolayers in a pH 8 phosphate buffer (ionic strength 0.1 M) solution containing 0.5 Mglucose. Scan rate 0.04 V sec. Temperature 25 °C. (a) Voltammograms for 0.2 mM ferrocene methanol mediator from bottom to top N = 0,2, 4, 6, 8, and 10 (for clarity, the odd numbers of monolayers are not represented).

Fig. 15 Variations of the catalytic plateau current in the cyclic voltammetry of ferrocene methanol in the presence of 0.5 M glucose in a phosphate buffer (pH = 8, ionic strength = 0.1 M), at 25 °C and a scan rate of 0.04 V sec at three different electrodes, (a) Electrode coated with 10 inactivated (Fg = 2.0 X 10 mol cm ) and 1 active (F° = 1.5 x 10 mol cm ) glucose oxidase monomolecular layers, (b) Electrode coated with 1-10 active glucose oxidase monomolecular layers (F = 1.5 x 10 mol cm ).

Fig. 16 Cyclic voltammetry of ferrocene methanol 0.2 mM in the absence of glucose and in pH 8 phosphate buffer (ionic strength 0.1 M) at a bare electrode ( ) and at a glucose oxidase electrode coated with 12 monolayers...

Fig. 18 Cyclic voltammetry of the catalysis of glucose oxidation at a glassy carbon disk electrode coated with 10 glucose oxidase monolayers in the presence of glucose and ferrocene methanol in pH 8.0 phosphate buffer (ionic strength, 0.1 M). Temperature 25 °C.

This electron transfer was positively affected by the immobilization of glucose oxidase on glassy carbon modified by aminophenyl boronic acid [193] or adsorption on to metalized carbons [194]. Nevertheless, it was possible to achieve good electron transfer only by modification ( functionalization ) of the enzyme with redox compounds (ferrocene derivatives). The direct electrical communication between the modified enzyme and an electrode has been proved by cyclic voltammetry. Thus attention was paid to the construction of various types of modified glucose oxidase electrodes. For instance, Benneto et al. [195] describe an... 

Cyclic voltammetry can be used to investigate if the mediator has a suitable redox potential, if the redox process is reversible, and to investigate if the rate-limiting step of the electron transfer is the chemical reaction at the electrode surface or the diffusion rate of the mediator to the electrode. In the most cases freely diffusing mediators are used. Efficient electron transfer has been demonstrated with mediators immobilized on lysine residues in glucose oxidase, and the... 

Figure 13.17 Cyclic voltammetry for increasing addition of glucose (from 0 to 25 mM), obtained at a glassy carbon electrode coated with an electrospun nanofibrous membrane in which glucose oxidase was immobilized. The dotted line is the signal of the mediator without the presence of glucose...

The catalysis of the oxidation of D-glucose by native and by recombinant glucose oxidase, mediated by one-electron redox co-substrates, has been monitored by cyclic voltammetry. A study on the effect of pH on the Pd-catalysed oxidation of D-glucose revealed that in acidic noedia the product, free D-gluconic acid, reversibly inhibits the oxidation process. ... 

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