Integrated microfluidic system for the simultaneous determination of ammonia, creatinine, and urea

An integrated sensing system for ammonia, creatinine, and urea incorporated in a micro-flow channel was microfabricated. The transducers for these sensors were air-gap Severinghaus-type ammonia sensors. The air gap was formed between the electrolyte solution for the ammonia sensor and sample solution. Creatinine demiminase and urease were immobilized at the bottom of the flow channel facing the indicator electrodes for the ammonia sensors. The concentrations of the three analytes were determined separately by taking differential outputs in the presence of the other chemicals. The solution pH in the system was changed by fabricating an active flow channel. A three-electrode system was formed at the bottom of the flow channel. The pH change was caused by applying a negative potential to an actuator electrode. By switching on the flow channel, a neutral sample solution became basic, and distinct responses were observed for the three sensors.