Early Sensing Of Tomato Late Blight Disease Based On Sensitized Olfactory Visual Electronic Nose Technology

Crop pathogens have always been the primary cause of reduced agricultural production worldwide,resulting in significant economic losses.To reduce these losses and effectively control plant pathogens,early detection of pathogenic microorganisms invading crops is of great significance.When pathogenic microorganisms invade crops,they rapidly decompose the nutrients such as sugars,proteins,or fats in the crops,producing various organic volatile gases such as alcohols,acids,aldehydes,and ketones.Different types of pathogenic microorganisms produce different types and amounts of organic volatile gases.Therefore,specific sensing of pathogenic microorganisms can be achieved by obtaining the fingerprint spectrum of the organic volatile gases produced after the invasion of crops by pathogenic microorganisms.By monitoring the organic volatile gases produced by crops invaded by pathogenic microorganisms at different stages,their changes can be identified,and early detection of pathogenic microorganisms affecting crops can be achieved.Traditional gas detection methods mainly use gas chromatography-mass spectrometry technology,which can accurately and specifically detect the gas to be tested.However,this requires expensive instruments and professional operators,which are not suitable for on-site rapid detection needs.Therefore,based on the principle of bionics,this article proposes the olfactory visualization technology to obtain the fingerprint spectrum of organic volatile gases produced after pathogenic microorganisms invade crops.Olfactory visualization uses color-sensitive materials to react with the gas to be detected,and qualitatively or quantitatively analyze the gas based on the color change of the color-sensitive material before and after the reaction,expressing the odor through an intuitive and visual image.This technology involves fixing color-sensitive materials on a substrate to form the sensor array.It has the advantages of rapid,high specificity,and simplicity,making it very suitable for on-site rapid detection needs.Traditional gas-sensitive materials include various dyes,such as p H indicators,vapochromic,and redox dyes.These dyes often have strong responses to gas with acidic or strong oxidizing or reducing properties（such as carboxylic acid,phosphoric acid,and amine）,but they are not sensitive to organic volatile gases released by diseased crops,such as alcohols,acids,aldehydes,and ketones.In response to the above issues,this paper takes tomato late blight as the research object and uses nanomaterials as a research tool to design and construct gas-sensitive materials with high sensitivity and response characteristics to characteristic organic volatile gases of late blight disease.The interaction mechanism between gas-sensitive materials and characteristic gas molecules is studied,and a high-specificity and multi-element sensitive array is constructed to achieve early sensing of the microbiological information of tomato late blight disease.The main research content and results of this paper are as follows:（1）In response to the problem that traditional dyes have little to no response to organic volatile gases such as aldehydes,alcohols,and esters released by crop diseases,a gas-sensitive material based on the nano-interface sensitization effect was constructed.The interaction between the gas-sensitive material and characteristic organic volatile gases was studied.A porous metal-organic framework（ZIF-8）with high surface area and stability was selected as the nano-sensitization material,and the dye was embedded in the nano-pores of ZIF-8 by a one-pot method to successfully synthesize the dye/ZIF-8 nanocomposite gas-sensitive material.Compared with traditional dye gas-sensitive materials,the newly constructed dye/ZIF-8nanocomposite gas-sensitive material increased the response sensitivity to organic volatile gases by at least 7 times.The interaction rules and sensitization mechanism between the nano-interface and characteristic gases were explored,laying the foundation for the construction of a highly sensitive method for detecting characteristic gases.（2）Based on the previous chapter,in order to solve the problem of active site blocking caused by the encapsulation of dyes in the nanointerface,a high-sensitivity and high-specificity sensor for crop disease characteristic gases such as aldehydes,alcohols,and esters is constructed based on the two-dimensional nanointerface sensitization effect.The dye molecules are fixed on the surface of two-dimensional metal-organic framework compound nanosheets（Zn₂（bim）₄）by physical adsorption,forming dye/Zn₂（bim）₄ nanocomposites.In the two-dimensional nanointerface,the two-dimensional metal-organic framework nanosheets have a large active surface area,which can further increase the contact probability between organic volatile gas molecules and dye molecules,thereby improving sensitivity.The dye/Zn₂（bim）₄ nanocomposite is drop-coated onto various substrate surfaces to prepare organic volatile gas sensors with high activity.The sensitivity of the sensor to tomato late blight characteristic gases such as aldehydes,alcohols,and esters is low,respectively:（E）-2-hexenal0.32 ppm,benzaldehyde 1.91 ppm,1-hexanal 1.75 ppm,（E）-2-hexenol 6.84 ppm,and methyl salicylate 0.52 ppm.This high-efficiency sensing characteristic of aldehydes,alcohols,and esters lays the foundation for early detection of tomato late blight in the future.（3）In order to solve the problem of low activity gas（such as benzene and olefin）perception difficulty in organic volatile compounds with crop disease characteristics,flexible metal-organic framework（MOF）sensors with intrinsic gas-sensitive structures were designed,and their interaction mechanisms with organic volatile gas molecules were studied.MOF materials with gas-sensitive structures were synthesized by molecular design.When combined with gas molecules,the molecular structure of the metal-organic framework changes,resulting in a color change at the macro level,achieving perception of low activity gases.Due to its unique gas-sensitive perception mechanism,it can effectively perceive low activity gases such as benzene and xylene that are not sensitive to dyes.In addition,the flexible metal framework gas-sensitive material has good reversibility for single volatile organic compounds and has the potential for repeated recycling.This efficient perception characteristic of low activity gases lays the foundation for early perception of tomato late blight in the later stage.（4）Based on the research contents of the above three chapters,the dye/metal-organic framework nanocomposite and gas-sensitive metal-organic framework compound prepared earlier were integrated to construct a sensing array for early perception of tomato late blight.For the characteristic organic volatile gases released by tomato late blight,such as aldehydes,alcohols,esters,ketones,and benzene gases,dye/metal-organic framework nanocomposites and gas-sensitive metal-organic framework compounds with high sensitivity response characteristics were selected respectively.The sensing array was integrated and prepared to obtain specific fingerprint spectra of diseased plants with different infection days and healthy plants.Combined with various data processing methods,the fingerprint spectrum information was deeply mined to achieve early perception of tomato late blight（within one day of inoculation）,and distinguish it from infections caused by other two types of tomato pathogens.