DETERMINATION OF UREA IN BLOOD-SERUM BY A UREASE BIOSENSOR BASED ON AN ION-SENSITIVE FIELD-EFFECT TRANSISTOR

A urease biosensor for the determination of urea in solutions and blood serum is made by immobilising urease in a bovine serum albumin membrane on the surface of an ion-sensitive field-effect transistor (ISFET). The sensor gives a linear response for concentrations of urea up to 2 mM at optimum parameters of the working buffer (10 mM potassium buffer, pH 7.4 with 200 mM NaCl). The high level of proteins in the serum decreases the biosensor response, but a 25-fold serum dilution gives reliable measurements. Twenty analyses can be made without a change in the sensor output. Repeated values do not differ by more than 10%. Urea measurements with the biosensor and the chemical urease-indophenol method show a high correlation. We propose that this biosensor is suitable for the medical determination of urea in blood serum.