Development of a transduction circuit for piezoresistive MEMS sensor for biosensing

This paper concerns the development of a potentiometric transduction circuit for a piezoresistive MEMS sensor to detect human stress. The biosensor is comprised of a bioreceptor and a transducer. The sensing principle is based on immobilization of the bioreceptor to produce a biochemical reaction. The novel piezoresistive microcantilever sensor integrated with a transduction circuit converts this biochemical event into a measurable electrical signal. From previous work, it has been found that the level of alpha amylase activity corresponds to human stress. The piezoresistive MEMS sensing and transduction method are described, with enzyme concentration as the input and voltage as the output. The transduction circuit designed enables the small change in resistivity due to the enzymatic reaction to be detected. The circuit has been designed and tested through theoretical, simulation and experimental studies. It has been found that for a sensor input range of 1.2 to 1.3 kilo ohms, an output range of -100 to +100 millivolts is obtained. A discrepancy within 3.69% is found between simulation and experimental results, on the average. The null bridge condition is designed at 1.2 kilo ohms while the offset rate is found to be 10 millivolts per ohm.