Portable urea biosensor based on the extended base bipolar junction transistor

In this study, an extended base bipolar junction transistor (EBBJT) was proposed to fabricate disposable urea biosensor. The detection of the urea is based on the variation of pH value. The gels, fabricated by the poly vinyl alcohol with pendent styrylpyridinium groups, were used to immobilize the urease. The SnO₂/ITO glass, fabricated by sputtering SnO₂ on the conductive ITO glass, was used as a pH-sensitive membrane for electrode, which is connected with a commercial bipolar junction transistor device. This readout circuit, fabricated in a 035-um CMOS 2P4M process, operated at 33V supply voltage. The circuit occupied an area of 1.0 mm × 0.9 mm. The dynamic range of the urea biosensor is from 1.4 to 64 mg/dl at the 10 mM phosphate buffer solution and the sensitivity of this range is about 65.8 mV/pUrea.