Oxygen-stabilized enzyme electrode

Cleland, N., Enfors, S.-0., Control of Glucose-Fed Batch Cultivations of E. coli by Means of an Oxygen Stabilized Enzyme Electrode , Eur. J. Appl. Microbiol. Biotechnol. 18 (1983) 141-147. 

The use of an electrode reaction offers the possibility to affect the enzyme reaction. In the oxygen-stabilized enzyme electrode the influence of the oxygen content of the sample solution is eliminated. For this purpose the same amount of oxygen as is consumed in the enzyme reaction is generated at a net electrode arranged within the enzyme layer. By using voltage pulses instead of a constant potential, both sensitivity and specificity of microenzyme electrodes can be improved. 

The measurements performed with the two types of biosensors show that the linear range of this type of enzyme electrodes using natural oxygen mediator manifest a wide range of measurement. The immobilised enzyme showed high operative stability, which makes the measurements easily reproducible. Both electrodes have very good correlation coefficients and a small standard deviation. 

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. 

Figure 3. Alcohol oxidase stabilization by mono-, di-, and trisaccharides. Sugars were added to the enzyme at concentrations of 1—10% immediately prior to drying. The solutions were dried in shallow dishes at 30 C under a vacuum and then harvested, ground to a powder, and stored in vials at 37 C. Enzyme activity was assayed with methanol as a substrate using an oxygen electrode and colorimetric assay.

Gorton et al. reported carbon paste electrodes based on Toluidine Blue O (TBO)-methacrylate co-polymers or ethylenediamine polymer derivative and NAD" " with yeast alcohol dehydrogenase for the analysis of ethanol [152,153] and with D-lactate dehydrogenase for the analysis of D-lactic acid [154]. Use of electrodes prepared with dye-modified polymeric electron transfer systems and NAD+/NADH to detect vitamin K and pyruvic acid has also been reported by Okamoto et al. [153]. Although these sensors showed acceptable performances, insensitivity to ambient oxygen concentration, sensor stability and lifetime still need to be improved to obtain optimal dehydrogenase based enzyme biosensors. 

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