Portable urea biosensor based on the extended-gate field effect transistor

In this study, extended-gate field effect transistor (EGFET) was applied to fabricate disposable urea biosensor. And the 1.5 V low-voltage instrument amplifier was adopted to realize the portable urea biosensor. However, the difference between extended-gate field effect transistor and traditional ion-selective field effect transistor is the position of the sensitive membrane. The extended-gate field effect transistor was separated into two parts, which are the sensitive membrane and MOSFET. Hence, the MOSFET device can be designed to be a part of the readout circuit and the sensitive membrane was only put in the solution. Therefore, the configuration of the extended-gate field effect transistor can reduce the influence of the temperature, light and the erosion by the solutions. Besides, the configuration can reduce the cost substantially. The configuration of the extended-gate field effect transistor will raise the competitiveness to develop the disposable biosensor. The content of the urea in blood is one of the indexes to diagnose the renal efficiency. Then, the portable urea biosensor is the important expandable aspect. In this study, the gels, which are the poly vinyl alcohol with pendent styrylpyridinium groups, were used to immobilize the urease. The detection of the urea is based on the variation of pH value. Then, the dynamic range of the urea biosensor is from 0.31 to 120 mg/dl at the 5 mM phosphate buffer solution and the response time is about 2 min. 2003 Published by Elsevier Science B.V.