Enzymatic Biosensor Based on the ISFET and Photopolymeric Membrane for the Determinaion of Urea

An ISFET based enzymatic biosensor was developed for the determination of urea. Immobilization of urease was accomplished by the use of liquid mixture which contained vinylpyrrolidone, oligouretane metacrylate and oligocarbonate metacrylate and which can form a polymer under the influence of ultraviolet. The biosensor has the following characteristics: the linear field of responses is in the range of 0.05–20 mM, curve slope – 38 mV/pC, and response time 5–10 min. The increase of the temperature from 28 to 41 °C leads to 15% increase in the intensity of the response of the biosensor. The maximum response is observed at pH 6.0–6.5. At the increase of the NaCl concentration in solution up to 300 mM the biosensor response drops off and achieves half of its initial level. NH₄Cl causes a stronger inhibition of enzyme activity comparing to NaCl. The results obtained with the developed biosensor correlate with the data of standard calorimetric methods. The intensity of the biosensor response decreases gradually during 40 days up to 80% of the initial level. The biosensors prepared with a fresh membrane or membrane preserved during 46 days at 2 °C gave similar responses in solution with an equal concentration of a substrate. It is concluded that the developed enzymatic biosensor is perspective for its clinical application for the determination of urea in blood and that the proposed method to prepare a selective biological membrane may be in a simple way included in integral technology of the semiconductor transducer manufacturing.