Research On The Aquatic Product Safety And Quality Detection Technology Based On Functional Semiconductor Nanomaterials And The Sensitive Mechanism

In the face of China’s vast aquatic product production and consumption market,how to ensure the safety and quality of aquatic products has become a hot and difficult issue.People all over the country pay close attention to the issue,which is closely related to national livelihood,international image,sustainable development and social stability.This research aims to achieve non-destructive and rapid detection of aquatic product safety quality,is based on the research on the synthesis and performance optimization of functional semiconductor nanomaterials,focuses on the detection performance of the constructed MOS gas sensor on actual aquatic product samples,and is supplemented by the research on the sensitivity mechanism of materials to the detection target of aquatic product safety quality.A new technology of aquatic product safety quality detection based on functional semiconductor nanomaterials has been constructed,which has solved an important problem in the field of food safety and quality detection.This research has great potential in ensuring the safety and quality of aquatic products in China.The main contents and conclusions of this study include:（1）Study on the synthesis and characterization of functional semiconductor nanomaterialsIn this research,Zn O materials with nanosheets（NS）,nanowires（NW）and nanocubes（NC）structures were successfully synthesized.The morphology,crystal form,specific surface area and other properties of these materials were characterized by SEM,TEM,XRD and N₂ isothermal adsorption analysis.It was found that the purity of the three kinds of materials was very high.Among them,Zn O NS and NW were uniform and stable,with very good crystallinity.However,the Zn O NC with more complex structure had comparatively poor stability and crystallinity.At the same time,WO₃ materials with nanosheets（NS）,nanorods（NR）and nanoflowers（NF）structures were successfully synthesized.It was found that the purity of the three kinds of materials was very high.Among them,structures of WO₃ NS and NR were uniform and stable,with very good crystallinity;However,WO₃ NF with complex structure are less stable and crystalline.Furthermore,Au,Pd and Pt nanoparticles（NPs）with high purity,uniform stability and good crystallinity were successfully synthesized.Three kinds of noble metal NPs were modified on different morphologies of Zn O and WO₃ nanomaterials.Then the compound materials characterized,which proved the successful preparation of Au/Zn O NS and Au/WO₃ NS.The N₂ isothermal adsorption analysis was used to calculate the specific surface area of Zn O and WO₃ nanomaterials before and after loading Au NPs.It was found that the specific surface area of Au/Zn O NS and Au/WO₃ NS were all significantly improved.These studies provided a material basis for the subsequent construction and performance research of MOS gas sensors.（2）Study on the construction and gas sensing performance of MOS gas sensor based on functional semiconductor nanomaterialsIn this study,MEMS-MOS gas sensors based on three noble metal NPs decorating different morphologies of Zn O nanomaterials were successfully constructed,and successfully used to detect 3-hydroxy-2-butanone（3H-2B）,which is the characteristic MVOCs（Microbial volatile organic compounds）of Listeria monocytogenes.The results showed that 1.0 wt%Au/Zn O NS sensors has the best gas sensing performance for 3H-2B.The response of the sensor to 25 ppm 3H-2B is up to 174.04 at 230℃.At the same time,it also has fast response recovery time（6s/7 s）,low detection limit（0.5 ppm）,excellent linear relationship and significant selectivity.Meanwhile,the author successfully constructed a side heated MOS gas sensor based on three noble metal NPs decorating WO₃ nanomaterials with different morphologies,and successfully used it to detect trimethylamine（TMA）,which is the indicator gas of aquatic product freshness evaluation.The results showed that the 2 wt%Au/WO₃ NS sensors has the best gas sensing performance for TMA.The sensor presented extremely high sensitivity at 300℃,with a maximum response of217.72,rapid response recovery time（8 s/6 s）,low detection limit（<0.5 ppm）and high selectivity.These studies had laid a solid foundation for the practical application of the constructed MOS gas sensor in the detection of the safety and quality of aquatic products.（3）Study on the practical application of MOS gas sensor in detecting the safety and quality of aquatic productsIn this study,the MEMS-MOS gas sensor based on 1.0 wt%Au/Zn O NS was successfully applied to the detection of Listeria monocytogenes in actual samples.Specifically,compared with the traditional culture method,the gas sensor detection result of Listeria monocytogenes in pure tryptone soybean broth showed a faster and obvious response（when the initial inoculation amount of bacteria was 10⁴ CFU/m L,the response value was significantly increased in 6 hours the fastest）.At the same time,the overall trend of the detection results of the two methods was the same,indicating that the detection of Listeria monocytogenes by gas sensor was feasible,accurate and fast.In addition,the sensitivity of the constructed gas sensor to Listeria monocytogenes was far greater than that to Vibrio parahaemolyticus,Escherichia coli and Salmonella spp.,confirming its outstanding selectivity to Listeria monocytogenes.Then,Listeria monocytogenes was artificially inoculated on salmon and Penaeus vannamei samples,and detected with the constructed gas sensor.At the growth temperature of 4℃and 25℃,within 18 hours of growth time,the sensor could produce obvious response to effectively detect the presence of Listeria monocytogenes,which verified the feasibility and accuracy of highly sensitive and highly selective detection of Listeria monocytogenes in aquatic products with MEMS-MOS gas sensor based on 1.0 wt%Au/Zn O NS.This excellent sensor has amazing application potential in real-time,nondestructive and efficient detection of Listeria monocytogenes,which opens up a new way for detection of Listeria monocytogenes in aquatic products and contributes to food safety worldwide.Meanwhile,the autuor successfully applied the side heated MOS gas sensor based on 2 wt%Au/WO₃ NS to evaluate the freshness of actual aquatic samples.Specifically,the gas sensor was very sensitive to volatile gases released by three common aquatic products,Pseudosciaena crocea,Pelteobagrus fulvidraco and Epinephelus spp.,under 25℃and 4℃storage conditions.At the same time,these responses had a very good linear relationship within 6 days.The volatile gases produced during the storage of these three species of fish were qualitatively and quantitatively analyzed by headspace gas chromatography-mass spectrometry.It was proved that TMA was the most important component in their volatile substances.Further,the correlation analysis between the quantitative analysis results of the headspace gas chromatography-mass spectrometry technology and the responses of the gas sensor was carried out.It revealed that the detection results of trimethylamine produced by three different samples under two different storage conditions within six days using two methods were significantly related,which proved the accuracy of the gas sensor in detecting trimethylamine released from actual samples of aquatic products.Therefore,the side heated MOS gas sensor based on 2 wt%Au/WO₃ NS had the ability to rapidly and nondestructively evaluate the freshness of aquatic products in real time by detecting trimethylamine,with very high feasibility and accuracy.This novel sensor opens up a new way for the freshness evaluation of aquatic products,and is of great significance for ensuring the safety of aquatic products in China and even the world.（4）Study on the sensing mechanism of MOS gas sensor based on functionalized semiconductor nanomaterials for the detection of the safety and quality of aquatic productsIn this study,the sensitive mechanisms of two types of MOS gas sensors that could detect the safety and quality of aquatic products were systematically explored,especially the mechanism of improving the material sensitivity after the modification of Au NPs.Based on the specific surface area data of 1.0 wt%Au/Zn O NS and 2 wt%Au/WO₃ NS,it was concluded that the two materials had more reactive sites and better gas sensing properties than similar materials.After that,the purity,element composition,type and proportion of oxygen species of these materials were further characterized by XPS.The results showed that the purity of the materials was very high for both 1.0 wt%Au/Zn O NS and 2 wt%Au/WO₃ NS.After the modification and functionalization of Au NPs,the active oxygen ions adsorbed on the surfaces of the two materials were significantly increased,effectively improving the sensitivity of the materials.The resistance changing trend diagram of the two materials also clearly exhibited that after the modification of Au NPs,the initial resistance of the two materials was significantly increased,while the response resistance in the target gas was significantly reduced.This phenomenon was due to the increase of active sites,active oxygen ions,the thickness of electron depletion layer and band gap.These conclusions more completely revealed the sensitive mechanism of the MEMS-MOS gas sensor based on 1.0 wt%Au/Zn O NS to the characteristic microbial volatile organic compounds of Listeria monocytogenes,and the sensitive mechanism of the side heated MOS gas sensor based on 2 wt%Au/WO₃ NS to the indicator gas TMA for evaluating the freshness of aquatic products.