REDUCING THE INFLUENCE OF SAMPLE OXYGEN IN BIOSENSOR DESIGN

This paper deals with principles of designing enzyme biosensors in which the effect of sample oxygen is reduced. A glucose sensor was developed consisting of two chambers for the sample and electrolyte solution, a semipermeable membrane dividing them, enzyme (glucose oxidase) dissolved in the electrolyte solution and an oxygen electrode. The behaviour of the biosensor was studied by analysis of a three-layer dynamic model and experimental investigations. It is demonstrated that the influence of sample oxygen is reduced when oxygen needed for the enzymatic reaction is supplied from the electrolyte solution and when transport of glucose and oxygen through the membrane is restricted. An additional decrease in this effect is also provided by choosing an optimal chamber volume ratio and by utilizing initial rates of oxygen consumption for detecting substrate concentration. The increase in the first derivative of the glucose sensor's current at pO2 = 40 mm Hg was about 2-3% compared with its value at pO2 = 145 mm Hg for samples containing 5 mM glucose. The operation of the biosensor under these conditions also provided greater measurement precision, an increase in the linear range of the calibrated curve and independence of measurements from a decrease in enzymatic activity. The calibrated curve of the glucose sensor was linear in the range 0. 1-25 mm. The accuracy of measurements within this range was +/- 1.8% and the relative standard deviation was +/- 1.3% at 5 mm. The manufactured glucose sensor is noted for many advantages, including rapid measurements and that no operation for the preparation of a sample or its dosage is necessary. The measurement time did not exceed 30 s. Only 20 mul of whole blood and 100 mul of enzyme solution are required for a single analysis. The biosensor remained stable for more than eight months at a storage temperature for the enzyme solution below 20-25-degrees-C.