Modified Glucose Oxidase Research Articles

Glucose sensor based on carbon paste electrode incorporating poly(ethylene glycol) -modified glucose oxidase and various mediators

Amperometric bioelectrodes constituted of carbon paste electrode incorporating poly(ethylene glycol)-modified glucose oxidase and mediators are studied. Influences of the nature of the mediators (anthraquinone, methylene blue, 2,6-dichloro-phenolindophenol, tetracyanoquinodimethane, 1,1'-dimethylferrocene) on the characteristics (potential window, apparent Michaelis constant, response time, stability) of the bioelectrodes are investigated. It is possible to show that the behaviour of the mediator is influenced by the pasting liquid contained in the carbon paste. Moreover, the water solubility of the mediator is the cause of a decrease of the apparent Michaelis constant in the case of methylene blue. A comparison between the stability of a low water soluble mediator (tetracyanoquinodimethane) and a more water soluble mediator (methylene blue) shows that the leakage of mediator from the carbon paste is not the cause of the lack of stability of such bioelectrodes. Among the various mediators tested, tetracyanoquinodimethane seems the most appropriate for the construction of a bioelectrode.

Amperometric glucose-sensing electrode based on carbon paste containing poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine

An amperometric enzyme electrode for glucose was prepared by incorporating poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine [CoPc(OEt) 8], a new mediator, into a carbon paste matrix. The polymer-modified enzyme exhibited a higher activity than the native enzyme in the hydrophobic carbon paste medium. CoPc(OEt) 8 could oxidize the enzyme at more negative potentials than unsubstituted cobalt phthalocyanine (CoPc). Further, the CoPc(OEt) 8-mediated enzyme electrode showed a high stability: the electrode response to glucose did not decrease for at least 4 weeks (or for 700 assays), whereas the glucose response from a CoPc-mediated enzyme electrode fell to half of the initial value within 2 weeks (or after 300 assays). CoPc(OEt) 8, a paraffin-oil soluble derivative of CoPc, incorporated in the bulk of carbon paste, diffused towards the electrode surface so as to renew continuously the electrode surface, which resulted in the high stability of the new mediator-based enzyme electrode.

Modifications to a carbon paste glucose-sensing enzyme electrode and a reduction in the electrochemical interference from L-ascorbate

A glucose-sensing enzyme electrode was prepared by incorporating polyethylene glycol-modified glucose oxidase, horseradish peroxidase and 1,1′-dimethylferrocene into a carbon paste. The modification of glucose oxidase with polyethylene glycol was effective for increasing the enzyme activity in the carbon paste owing to the enhanced affinity of the polyethylene glycol-modified enzyme for the hydrophobic carbon paste matrix. In contrast, however, the enzyme activity of the polymer-modified peroxidase was lower than the unmodified peroxidase in the carbon paste matrix because of a severe loss of the enzyme activity during the modification with polyethylene glycol. Hence, the enzyme pair of polyethylene glycol-modified glucose oxidase and unmodified peroxidase was used for preparing the enzyme electrode. The reductive current response of the electrode to glucose was recorded at 0·2 V vs. Ag/AgCl. After the addition of glucose (100 μM), the current increased immediately and reached a plateau ( Δ = −0·12 μA) within 30 s. The current response was linear up to a glucose concentration of 500 μM and the detection limit was 20 μM (S/N = 5). Interference from ascorbate was very small: the current response to 1 mM glucose (−1·1 μA) was slightly reduced to −0·9 μA when 1 mM ascorbate was added to the glucose-containing solution. In biological and food samples, the concentration of ascorbate is generally quite low compared with the glucose concentration. The interference from ascorbate could actually be ignored for the purpose of determining glucose in soft drinks.

Japan — Carbon paste electrode : In ANAL. CHIM. ACTA (300/1–3 (59–64) 1995) F. Mizutani, S. Yabuki & S. Iijima of National Institute of Bioscience, Human-Technology, report on “Amperometric glucose-sensing electrode based on carbon paste containing poly(ethylene glycol)-modified glucose oxidase and cobalt octaethyoxyphthalocyanine”

Japan — Carbon paste electrode : In ANAL. CHIM. ACTA (300/1–3 (59–64) 1995) F. Mizutani, S. Yabuki & S. Iijima of National Institute of Bioscience, Human-Technology, report on “Amperometric glucose-sensing electrode based on carbon paste containing poly(ethylene glycol)-modified glucose oxidase and cobalt octaethyoxyphthalocyanine”

Japan—Glucose sensor based on carbon paste electrode : In ANAL. CHIM. ACTA (304/1 (33–39) 1995) C. Saby, F. Mizutani and S. Yabuki of the National Institute Bioscience report on “Glucose sensor based on carbon paste electrode incorporating poly(ethylene glycol)-modified glucose oxidase and various mediators”

Japan—Glucose sensor based on carbon paste electrode : In ANAL. CHIM. ACTA (304/1 (33–39) 1995) C. Saby, F. Mizutani and S. Yabuki of the National Institute Bioscience report on “Glucose sensor based on carbon paste electrode incorporating poly(ethylene glycol)-modified glucose oxidase and various mediators”

Some studies of electrodes made from single crystals of TTF /sd TCNQ

Electrodes made from single crystals of tetrathiafulvalenium tetracyanoquinodimethanide (TTF. TCNQ) have been used to study the electrochemistry of the conducting organic salt and to investigate the mechanism of the electrochemical oxidation of glucose oxidase at conducting salt electrodes. The single crystal electrodes exhibit much lower non-Faradaic currents than the corresponding polycrystalline electrodes prepared as sublimed films or as pressed pellets. This leads to much lower background current levels and hence more clearly defined electrochemistry for solution species. Studies of the ac impedance behaviour and the electrochemistry of outer sphere redox species indicate that TTF·TCNQ electrodes behave as conventional metallic electrodes within their stable potential range. Results for the electrochemistry of glucose oxidase at the single crystal electrodes are inconsistent with a simple homogeneous mediation mechanism or with simple heterogeneous redox catalysis. Similarities with results obtained for TTF modified glucose oxidase suggest that the enzyme may undergo direct electrochemistry after modification by hydrophobic interaction with TTF molecules derived from the conducting salt electrode.

The use of redox mediator modified glucose oxidase in amperometric enzyme electrodes

Glucose oxidase, modified by the covalent attachment of ferrocenyl groups, has been shown to undergo direct oxidation at clean metal electrodes (Degani & Heller 1987, 1988; Bartlett et al . 1987). Since modified enzymes of this type do not require a freely diffusing mediator and can be oxidized at modest overpotentials they are attractive for application in biosensors and in bioelectronics. The use of ferrocene monocarboxylic acid and ferrocene acetic acid modified glucose oxidase has been studied in membrane enzyme electrodes for glucose. It was found that the lifetime of these devices is limited by the stability of the oxidized form of the ferrocenyl substituent attached to the enzyme. In buffered aqueous solution this is of the order of minutes for the ferrocene monocarboxylic acid modified enzyme and of the order of hours for the ferrocene acetic acid modified material.

Modification of glucose oxidase by tetrathiafulvalene

Treatment of glucose oxidase with tetrathiafulvalene (TTF) in aqueous buffered solution leads to modification of the enzyme by incorporation of TTF molecules; the resulting modified enzyme undergoes direct oxidation at metallic electrodes and can be used to sense glucose.

Covalent binding of electron relays to glucose oxidase

Modification of glucose oxidase by the covalent coupling of ferrocenecarboxylic acids gives mediator modified enzymes which undergo direct oxidation at an electrode; the use of ferroceneacetic acid instead of ferrocenecarboxylic acid is an improvement in terms of the overpotential for oxidation, the reactivity towards glucose, and the stability on storage.

Detergent-containing glucose oxidase reagent for use with the Beckman glucose analyzer.

We describe a modified glucose oxidase reagent for use in the polarographic determination of glucose with the Beckman "Glucose Analyzer." The reagent contains 1 mL/L of a surfactant (Brij-35 250 g/L solution) as the wetting agent instead of glycerol. Precipitation of components associated with the formulation recommended by Fischl et al. [Clin. Chem. 21, 760 (1975)] does not occur with this reagent. It can be used immediately after preparation. When compared to analytical performance of the commercially prepared reagent, the precision was unchanged by the modified reagent, but the upper limit of accurate response was diminished (7.5 g/L vs. 6.7 g/L). The modified reagent is less expensive than are commercially prepared reagents.

Preparation of a Modified Glucose Oxidase Reagent for the Polarographic Determination of Glucose with the Beckman "Glucose Analyzer"

In this modification, glucose oxidase, 140-180 U/ml, is dissolved in acetate buffer (pH 6):ethanol (96%):glycerol (80:10:10 by vol). Iodine and molybdate are used as catalysts, formaldehyde and mercuric iodide as preservatives, and octanol as an antifoaming agent. The reagent is suitable for use in the Beckman "Glucose Analyzer", it is stable at room temperature for at least six months, it is sensitive, it has a lubricating effect, and its cost is less than a fifth as much as the "Certified" Beckman reagent. It is not suitable for the measurement of glucose in samples containing maltose, cellobiose, gentiobiose, starch, and glycogen.

Modified Glucose Oxidase Method for Determination of Glucose in Whole Blood

Abstract We have modified an ultramicro method for determining glucose with glucose oxidase—peroxidase—odianisidine. Capillary blood is diluted in isotonic NaF (17.6-17.8 g/ liter), the cells are removed, and glucose is determined after a 20-min incubation with enzyme-containing reagent. Increasing the enzyme concentration fourfold nullifies interference from ascorbic acid and hemolysis, while greatly decreasing interference from bilirubinemia. If necessary, bilirubin is removed completely by coprecipitation with protein. Interference from uric acid is minimized by incorporating it into the standards. Several other suspected interferences proved inconsequential. Isotonic NaF does not inhibit the enzymes used, and preserves glucose in blood for at least 2 h. Avoiding protein precipitation and shortening the incubating time significantly lessens analytical time without affecting precision.