Construction And Synergistic Mechanism Study Of Targeted Pesticide Delivery System With Leaf Adhesion

Pesticides have played a substantial role in meeting the food needs of the world's growing population.However,about 70% of the effective components in the traditional pesticide formulations cannot accurately reach the target crops due to erosion,migration,volatilization and other reasons,and only about 0.1% of the effective components are harmful to target organisms.The loss of pesticides into the environment and ecosystems has brought great latent danger to the environment,other non-target organisms and human health.Therefore,improving the adhesion of pesticides to target crop leaves can increase the deposition of pesticides and retention time on crop leaves,control the release rate of pesticides,and prolong exposure time of pesticides,ultimately giving rise to improving the effective utilization of pesticides.In this thesis,based on the high-performance and multi-functional targeted pesticide delivery system with leaf adhesion,the release behavior and indoor biological activity of the drug loading system were measured.Fluorescence imaging technology was used to study the interaction mechanism of the surface groups of the pesticide delivery system and the leaf surface,and analyze the deposition and retention behavior of the pesticide delivery system.The results are shown as follows:1.The poly(styrene-co-methacrylic acid)and poly(lactic acid)were used as the carrier materials,and the avermectin was selected as the model pesticide.Three bio-inspired amphiphilic Janus nano drug delivery systems(P(St-MAA)-PLA,P(St-MAA)-PLA-Cat and P(St-MAA)-PLA-Cat-PN)with leaf adhesion were fabricated by chemical modification on the surface of crop leaf.The average particle size was about 100 nm,and the ? potentials were-25±1.1,-13±0.8,and-10±0.7 m V,respectively.All of which have better photostability and slow-release performance.Due to P(St-MAA)-PLA-Cat-PN nanoparticles can effectively form hydrogen bonds with polar groups on plant leaf surface,the retention amount on cucumber leaf surface can reach more than 45%.2.Combined with environmentally responsive controlled release technology,chitosan oligosaccharide was selected as the carrier material,and avermectin was encapulated to prepare a pH-responsive pesticide nanocapsule delivery system with leaf adhesion(Av-pH-cat@CS).The average particle size was about 220 nm and the drug-loading rate was more than 30%.The Av-pH-cat@CS nanocapsules exhibited good pH-responsive controlled release performance and adhesion to crop leaf surfaces.The pest control efficacy of avermectin loaded in Av-pH-cat@CS nanocapsules was significantly enhanced at low pH,owing to the rapid release and improved retention rate.The adhesive force of Av-pH-cat@CS nanocapsules to crop leaf surfaces was mainly a result of hydrogen bonding.The affinity of Av-pH@CS nanocapsules for the leaf surface led to longer retention times,which may enhance the utilization efficiency of the pesticide.3.L-ascorbyl palmitate was chosen as the carrier material to prepare enzyme-responsive leaf adhesive hydrogel drug delivery system(Av-Eny-cat@AP)and bacterial affinity leaf phospholipid hydrogel drug delivery system(AZX-Eny-cat@AP).Av-Eny-cat@AP and AZX-Eny-cat@AP could release active components in a dose-dependent manner only in the presence of esterase,resulting from the decomposition of hydrogel structure.The retention rate of Av-Eny-cat@AP on the surface of a variety of different hydrophilic and hydrophobic leaves including cucumber,cabbage,corn,tomato,pepper,grape,rice,were measured by fluorescene imaging intensity with Rhodamine 6G used for fluorescence labeling.The retention rate of Av-Eny-cat@AP on cucumber,cabbage,corn,tomato,pepper,grape,rice leaf surface were 93.44%,77.28%,83.53%,85.55%,92.31%,70.69%,91.07%,respectively.The retention rate of AZX-Eny-cat@AP hydrogel were 62.98%,70.19%,93.98 %,91.74%,77.93%,96.82%,92.06%,respectively.The adhesive force is mainly from the hydrogen bond between ascorbyl group of AP and polar groups of leaf wax layer,and the hydrophobic interaction between palmitate of AP and long carbon chain of leaf wax layer,which leads to strong adhesion and high retention rate.