Research On The Application Of Two-dimension Metal-organic Frameworks Based Biosensors In Food Safety Detection

Recently,with the rapid development of nanotechnology,high-performance biosensors based on various new materials have become research hotspots in analytical chemistry,food safety,environmental monitoring and clinical diagnosis.Metal-organic frameworks(MOFs)are a type of crystalline porous material with periodic network structure formed by inorganic metal centers(metal ions or metal clusters)and bridging organic ligands connected to each other through self-assembly.Usually,MOFs possess both the rigidity of inorganic materials and the flexibility of organic materials.Thus,MOFs have attracted attention because of their unique structure and physical and chemical properties,which can be used as efficient nanozymes,fluorescence quenchers,electrochemical signal mediators and enzyme immobilization substrates to participate in the construction of biosensors.Notably,compared with three-dimensional bulk MOFs,MOFs with two-dimensional sheet structure(2D MOFs)not only have superior enzyme-like catalytic activity,but also have a higher fluorescence quenching efficiency.Also,compared with traditional biological enzymes,2D MOFs also have the advantages of low cost,easy storage,and easy preparation.Our research work used its outstanding characteristics to construct three high-performance biosensors for food safety applications.The main research contents are as follows:(1)Colorimetric quantification of sodium benzoate in food by using D-amino acid oxidase and 2D metal organic framework nanosheets mediated cascade enzyme reactionsA rapid colorimetric method for detecting sodium benzoate in food products was established based on the D-amino acid oxidase(DAAO)and 2D metal organic framework(2D MOF)nanosheets mediated cascade enzyme reactions.Firstly,the synthesized 2D MOF nanosheets served as highly efficient nanozyme with outstanding peroxidase-like catalytic activity and catalyzed the color reaction between H₂O₂ and 3,3',5,5'-tetramethylbenzidine.Secondly,sodium benzoate as a competitive inhibitor of DAAO,could influence the production of H₂O₂ in DAAO mediated oxidation reaction.After a combination of those two reactions,this colorimetric quantitative method was constructed and validated for sodium benzoate determination with wide linear range(2.0-200.0?M),low limit of detection(2.0?M),high accuracy(recovery rate in 95.80-108.00%)and satisfied selectivity.Lastly,this method was utilized to analyze sodium benzoate concentration in juice,wine and vinegar by naked eyes.(2)Comparative study on the activity of hybrid nanozymes formed by Au NPs of different particle sizes and 2D MOF and their application in the detection of organophosphorus pesticidesThrough different preparation methods,two kinds of gold nanoparticles(Au NPs)with different size were generated in situ on the surface of 2D MOF,forming two composite nanozymes with different activities.By analyzing the dynamic and mechanical parameters of the enzyme reaction of these two composite nanozymes and exploring the mechanism of the difference in catalytic activity,it was clear that the particle size of Au NPs affects the catalytic performance of the composite nanozyme.Next,ultrasmall gold nanoparticles/2D MOF complex(Us Au NPs/2D MOF)with outstanding peroxidase-like activity was selected to form a ternary cascade reaction system with acetylcholinesterase(ACh E)and choline oxidase(CHOx).In response,based on the inhibitory effect of organophosphorus pesticides on ACh E,a fast and ultra-sensitive colorimetric method was established to detect trichlorfon in fruits and vegetables.The detection method had the advantages of simple operation,low detection limit(0.4ppm),high accuracy(recovery rate of 96.6-105.3%)and so on.Finally,this method could be applied to the visual analysis of the concentration of trichlorfon in pears,apples,and cabbage.(3)2D MOF-based aptamer sensor for fluorescence and visual double signal detection of mercury in riceSince 2D MOF has both peroxidase-like catalytic activity and fluorescence quenching performance,a fluorescence-visual dual-signal sensor can be constructed based on this material.In this regard,we had carried out pre-experimental research work.The experimental results showed that 2D MOF had a very significant fluorescence quenching effect on 6-carboxyfluorescein-labeled Hg²⁺Aptamer.With the addition of Hg²⁺,an obvious fluorescence signal recovery was present.This phenomenon was feasible for the double signal sensor applied to the detection of mercury in rice.