Miniature urea sensor based on H(+)-ion sensitive field effect transistor and its application in clinical analysis.

An urea-ENFET (Enzyme field effect transistor) probe was made by covering one of the grids of the dual ISFET (Ion sensitive field effect transistor) with a membrane of cross-linked bovine serum albumin (BSA)-urease and the other with cross-linked BSA, and the response characteristics of the probe was then tested through differential measurements. In different concentrations of phosphate buffer, the sensor responded to various concentrations of urea solution within 10-60s. From the calibration curve plotted on logarithmic scales a linear concentration range of 1.0-8.0 mg/dl was acquired, and the correlation coefficient and response sensitivity were 0.997 and 50mV/dec. (mg/dl), respectively. However, in dilute urea solution, the sensor responded linearly to the contents of urea over the range of concentration of 0.1-1.0 mg/dl with a correlation coefficient of 0.998 and a response sensitivity of 12-15mV/mg/dl. The standard deviation and the variation coefficient for 20 performances responding to 100mg/dl urea in 0.01M pH7.0 phosphate buffer were found to be 1.39mV and 1.44%, respectively. The urea-ENFET was used for the determination of BUN (Blood urea nitrogen) and the BUN values were compared with those determined by enzymatic method, the repression equation and correlation coefficient for 50 assays were y = -0.1272 + 0.9695x and r = 0.9912, respectively. When the urea-ENFET was used for determining urea either in buffer solution or in serum for 250 runs over a period of 1.5 months (the enzyme FET was stored at 4 degrees C between measurements during this period), the observed decrease of response sensitivity was only about 10%.(ABSTRACT TRUNCATED AT 250 WORDS)