Study On Medical Electronic Nose And The Sensitivity Of Gas Sensor

Electronic nose has been widely used for the quality control of environment, food, etc... However, the medical electronic nose used for disease diagnosis is still at its infancy, under research in laboratory. This project studied and designed a prototype of medical electronic nose. The key points of research work were the sensitivity and the lowest detection limit (LOD) of metal oxide semiconductor sensor (MOS). Aiming at mammary cancer, we selected the gas sensors used in the electronic nose system and designed the sensor array.This paper demonstrated the feasibility of medical electronic nose from the pathology point of view, described its development and existing problems. The principle of its working was described in detail.TGS822 was used to test the performance of MOS sensor, including its resistance characteristics, repeatability and stability, focuing on the sensitivity and the LOD. Research shows that TGS822 is very sensitive to ethanol gas, and LOD of ethanol gas is 61ppb. Heating voltage does have some effects to the sensitivity of MOS sensor. With the heating voltage varying from 3.5V to 5.5V, the sensor's sensitivity first rises and then decreases, which means there is an optimum heating voltage. Several sampling circuits and their effects to the sensitivity of the sensor were analyzed. A double-sensor circuit was used. Compared with traditional methods, the sensitivity of the sensor was considerably enhanced.Aiming at the examination of mammary cancer, current available types of gas sensors were studied, such as MOS and QCM, etc... Finally senven gas sensors, TGS822, TGS2620, TGS2602, TGS2600 (produced by Figaro company), QS-01(produced by FIS company), Gsbt11 (produced by OGMA company in Korea), 4ETO (roduced by CITY company) were selected to form up sensor array in our system, to detect the volatile biomarker in patients' exhalation.As the concentration of volatile biomarkers in patients' exhalation is very low (in ppb to ppt level), very low lever of LOD is required for sensors used in electronic nose. But such LOD can not be achieved with current gas sensors. This thesis set forth the indispensability of pre-concentration.During the data analysis, while the output signals of sensors were not stable enough, the multi-point moving average technique was employed to pretreat the original signal from sensors.