The Development Of Gas Detection System Based On QCM Sensors And Its Application In Egg Quality Evaluation

Artificial olfactory system based on gas sensor array has been widely used in nondestructive evaluation of food stuffs.The evaluation process can be achieved through testing gas released from food,which provide direct and helpful information about food quality.Electronic nose is a common artificial olfactory system.The majority of electronic nose systems employ metal oxide semiconductor(MOS)gas sensor array,which works under high temperature in a range of 200?500 ?,resulting in high power consumption,relatively low sensitivity and slow response rate.Given that circumstances,quartz crystal microbalance(QCM)gas sensors with high sensitivity and low operating temperature were employed to solve the problem of high working temperature and low sensitivity in MOS sensors.In this research,a gas detection system for QCM sensor array was developed,an array of QCM gas sensors was fabricated and applied to achieve the nondestructive evaluation of egg quality.The main conclusions of the research are as follows.Firstly,a gas detection system for QCM sensor array was developed,which included a crystal oscillator circuit,a frequency measuring module based on FPGA,a MCU processor module and Lab VIEW software.The system was capable of actuating QCM sensors,measuring resonant frequency,displaying response curves,data logging and data analysis.Secondly,four QCM sensors,modified with copper oxide,carbon nanotubes,polyaniline and graphene sensitive film,were fabricated by dip-coating method and characterized under field emission scanning electron microscope.The sensitive materials dispersed uniformly on the electrode and exhibited good morphology.The optimum number of coating layers were determined by studying the response time and response value through a set of experiments.We also tested the responses of the four sensors when exposed to ethanol,ammonia,hydrogen sulfide and dimethylamine gas,and investigated the sensitivity,repeatability,reversibility,selectivity and long-term stability of the four QCM sensors.These sensors were proved to have good gas sensing properties and high reliability,together formed a QCM sensor array and were applied in further researches.Finally,the fabricated QCM sensor array and developed QCM gas detection system were applied to evaluate the quality of eggs with different shelf life and different producing areas.In the procedure of shelf life evaluation,PCA and LDA method could help to classify eggs of different shelf life.PLSR and KPCA method were employed to establish regression model,which exhibited promising accuracy in the process of shelf life prediction.In the procedure of evaluation in egg producing area,LDA method showed good performance in classification,and ELM method exhibited high classification accuracy in discriminating eggs with different producing areas.In conclusion,a nondestructive and effective evaluation of egg quality was successfully achieved by the fabricated QCM sensor array,which was a convenient approach and probably helpful for the further study of QCM sensors and the study of food quality evaluation.