Construction Of Nanoparticle Pesticides Dilivery Systems And Its Application For Controlling Avermectin Release

The utilization rate of traditional pesticides is only about 20-30%,which is mainly affected by environmental factors,such as sun,wind,spray and so on,resulting in pesticides waste and environmental pollution.Avermectin is a substitute product of highly toxic pesticides determined by the Ministry of Agriculture.It has the advantages of broad spectrum,low toxicity,high efficiency and high selectivity.However,because of its sensitivity to light,it is easy to decompose in the process of practical application and has a short residual period.Less deposition on the target and other shortcomings.In order to solve these problems,we designed and prepared nano-organic-inorganic hybrid sustained-release avermectin system with UV photodegradation resistance,deposition property at plant interface and controllable release.In this paper,the construction of nanoscale sustained-release avermectin system and the application of drug delivery were studied.The main tasks are as follows:（1）Construction of avermectin/hollow nano SiO₂（h-SiO₂）system.Polystyrene as hard template and ethyl orthosilicate as silicon source,h-SiO₂ nanospheres were prepared by hard template method.The microspheres are white powder,amorphous and hollow spherical,the average particle size is 120-130 nm,the wall thickness is about 15 nm,and the surface is rough.The cumulative release rate of avermectin was 40.3%after 72 h,and 25%was undegraded after UV degradation after 20 h.The mechanism of sustained release of abamectin was studied.The wetting and depositional properties of the hydrophilic plants were similar to those of the commercial water emulsion of avermectin（EW）.The leaf surface deposition of hydrophilic plants was 41.5%and 21.4%,respectively.（2）Construction ofβ-cyclodextrin/h-SiO₂ system.In order to increase the loading of abamectin,β-cyclodextrin structure was introduced into h-SiO₂.The preparedβ-cyclodextrin/h-SiO₂ nanospheres were hollow microspheres with rough surface and regular morphology.Because cyclodextrin provided the adsorption center for avermectin,the adsorption rate was increased by about 20%.The cumulative release rate of avermectin was37.4%after 72 h.The contact angles with hydrophilic or hydrophobic plant leaf surface were 77.35±4.1°and 99.84±3.2°,respectively,and the sedimentation rates were 49.1%and 25.1%,respectively.（3）Construction of polyethyleneimine/h-SiO₂ system.In order to improve the deposition of Avm on plant leaves,isocyanate groups were introduced into the surface of h-SiO₂ and then reacted with polyethyleneimine to prepare polyethyleneimine/h-SiO₂ nanospheres.The carrier has a regular hollow spherical structure,polyvinyleneimide can delay the release of avermectin and has a pH response behavior.The deposition rates on the hydrophilic and hydrophobic leaf of purple cabbage and hydrophobic leaf of euphorbia milii were 63.4%and32.8%,respectively.（4）Studies on the avermectin loading system of chitosan/Avm-PDA@h-SiO₂ Composite microgel.Dopamine was coated on h-SiO₂ microspheres by oxidation self-polymerization,which not only provided the adsorption site for avermectin,but also increased the adhesion on plant surface,and then coated chitosan microgel.The slow release and UV photodegradation resistance of avermectin were improved,and the pH response behavior was also observed.The rate of slow release was faster under alkaline condition,and about 20%was degraded after UV degradation for 20 h.The sedimentation rate of purple cabbage on hydrophilic leaf surface was 60.3%,which showed good adhesion.（5）Construction of temperature responsive PNIPAm/h-SiO₂ nanocarriers.Hollow PNIPAm/h-SiO₂ nanospheres with rough surface and regular morphology were prepared by click reaction of mercapto-double bond.When the release temperature is 40℃,the release rate is slower and the cumulative release amount is 30%.The deposition rates at the hydrophilic and hydrophobic surfaces were 42.3%and 23.4%,respectively,which were similar to those of the commercial avermectin emulsion EW.In summary,a series of sustained-release abamectin systems were constructed based h-SiO₂ microspheres with the principle of organic-inorganic hybrid binary coordination.The study shows that the constructed nanoscale delivery systems have the functions of sustained release,UV photodegradation resistance and deposition property at plant interface.The research provides a reference for the application of nanoscale sustained-release drug systems in agricultural production.