Rapid Detection Of TVB-N In Fish Based On QCM Gas Sensor

Fish meat is extremely prone to produce many total volatile base nitrogen(TVB-N)compounds with low content during production,processing,transportation,storage,and other processes.TVB-N is a physicochemical index that can reflect the quality of fish meat.TVB-N is mainly composed of trimethylamine(TMA),dimethylamine,ammonia,and other nitrogen containing chemicals,and these chemicals can be converted to gases under alkaline conditions.It is of great significance to develop high-performance gas sensors for the detection of TVB-N in fish meat.Traditional testing methods take a long time and waste manpower when testing a large number of samples.The quartz crystal microbalance(QCM)gas sensor can detect changes in mass at the level of nanograms,making it suitable for detecting trace TVB-N gases when fish meat decays.In this paper,QCM gold electrode is used as the substrate of gas sensor,and sensitive materials are coated on the substrate surface by drop coating method.Two types of gas sensors were constructed to detect the marker volatile substances TMA and TVB-N during the decay of salmon,respectively,to determine the freshness of salmon meat.The main research contents and results are as follows:(1)Graphene oxide(GO)with nanoscale pores had a good adsorption effect on TMA,and had a certain selectivity for TMA.Nanoporous graphene oxide(NGO)was successfully synthesized and a QCM gas sensor was prepared using a drop coating method for the detection of TMA,aiming to form a reliable monitoring system that could still cause high response when the concentration of TMA was low.Compared to GO based QCM gas sensors,the NGO based QCM gas sensors had ultra-high sensitivity to TMA(3～4 times higher than GO based QCM gas sensors),excellent linearity(R2=0.98),high response/recovery ability(3 s/20 s),and excellent repeatability(RSD=0.02,n=3).Moreover,the resistance of the NGO based QCM gas sensor also had a certain response signal,thereby achieving a dual signal monitoring.By contrast,the QCM gas sensor based on GO had nearly no resistance response signal.In addition,the selectivity of the NGO based gas sensor towards TMA was verified through dual signal response analysis.This work confirmed that the proposed QCM gas sensor based on functionalization of NGO nanomaterials for TMA detection was a new approach.(2)TVB-N is a marker of salmon meat spoilage that contains TMA,dimethylamine,ammonia,and other nitrogen containing chemicals.NGO had a good adsorption effect on TMA,and had a better response towards dimethylamine compared to other interfering gases,while molybdenum disulfide(MoS2)had a better adsorption effect on ammonia and other nitrogen containing gases.A porous NGO/MoS2 composite was successfully synthesized using a onestep hydrothermal method,and the QCM gas sensor based on the NGO/MoS2 composite was prepared using the same method for detecting TVB-N.It was found that NGO/MoS2 composite had edge sites,functional groups,and active sites on the surfaces of GO and MoS2,which were conducive to adsorbing the target gases.The QCM gas sensor based on NGO/MoS2 had excellent sensitivity to TVB-N gas(nearly 2 times higher than both MoS2 and NGO),excellent linearity(R2=0.96),high response/recovery ability(2 s/15 s),and excellent repeatability(RSD=0.04,n=3).The QCM gas sensor based on NGO/MoS2 and an automatic Kjeldahl nitrogen analyzer with national standard methods were both applied to detect the same salmon samples.By comparing data from 0 to 5 days of salmon meat,it could be judged that the corruption degree of salmon meat increased with time went by.On day 4,the results of both methods showed that the salmon meat was rotten,and The TVB-N content exceeded the national standard.The QCM gas sensor based on NGO/MOS2 provides a new idea for predicting the freshness of salmon meat.In summary,nanoporous materials could effectively adsorb TMA and TVB-N,and the prepared materials based QCM gas sensors were able to detect the marker volatile substances in salmon meat,thereby determining the freshness of salmon meat.