Construction And Application Of Environmentally Responsive Nano-controlled Release Formulation Of Emamectin Benzoate

Corn is one of the important grain crops at present.In recent years,the explosive spread of Spodoptera frugiperda has caused a significant decline in corn yield and quality.Emamectin benzoate（EB）is one of the recommended insecticides by the Ministry of Agriculture and Rural Affairs of China for the control of S.frugiperda,and has played an important role in the control of S.frugiperda.However,there are many shortcomings in the conventional formulations of EB,such as high usage of organic solvents and emulsifiers,poor environmental compatibility,etc.In addition,the conventional formulations do not have slow and controlled release function,and the active ingredients are easily lost by photolysis and hydrolysis in the environment,resulting in reduced control effect.Mesoporous silica nanoparticles（MSNs）are used as common carrier for slow and controlled release of pesticide with good biocompatibility,high loading efficiency and easy surface modification.However,it is difficult to achieve precise release of pesticide by MSNs alone.By modifying MSNs,nanoparticles can achieve the effect of controlled release of pesticides in response to environmental stimuli.Based on the above,MSNs were prepared by sol-gel method in this study.To prepare temperature-responsive,pH-responsive and α-amylase-responsive emamectin benzoate controlled release formulation,（NIPAAM-MAA）,（GMA-AA）and（α-CD）were grafted onto the surface of MSNs respectively.The physicochemical properties of the nanoparticles were characterized by TEM,BET,FTIR and TGA.Then,the release properties,anti-photolysis and biological activity against Spodoptera frugiperda of three kinds of EB-loaded nanoparticles were tested.Finally,their biosafety to non-target organisms examined.The results of this study are as follows:（1）Temperature-responsive EB controlled release formulation（EB@MSNs@K（NIPAAMMAA））was prepared by sol-gel method and surface modification,and microscopic morphology observation showed that the unloaded particles MSNs@K（NIPAAM-MAA）were round in shape,uniform in size and rough in surface,and the thermosensitive polymer NIPAAM-MAA was grafted to the surface of MSNs,the particle size is distributed in the range of 170-190 nm.The results of BET,FTIR and TGA also showed that the thermosensitive polymer was successfully grafted（grafting rate of 19.5%）and EB was successfully loaded into MSNs（drug loading of 15.7%）.Release behavior studies showed that higher temperatures（28 and 24℃）were favorable for EB release.The contact angle of EB@MSNs@K（NIPAAMMAA）on corn leaves was less than that of EB@MSNs on corn leaves,indicating that EB@MSNs@K（NIPAAM-MAA）had better spread properties on corn leaves.Both commercial EB@EC and EB@MSNs@K（NIPAAM-MAA）,had reasonable control effect against S.frugiperda at the same concentration,but the insecticidal effect of EB@EC was lower than that of EB@MSNs@K（NIPAAM-MAA）with time extension,indicating that EB@MSNs@K（NIPAAM-MAA）had a longer effective duration（14 d）.The biosafety test showed that the LC50 of EB@MSNs@K（NIPAAM-MAA）was 26.62 mg/kg at 14 d on earthworms,which showed low toxicity.In addition,EB@MSNs@K（NIPAAM-MAA）had no significant effect on the changes in chlorophyll content of corn leaves at a range of concentrations.（2）pH-responsive EB controlled release formulation（EB@MSNs@K（GMA-AA））was prepared by sol-gel method and surface modification,and microscopic morphology observation showed that the unloaded particles MSNs@K（GMA-AA）were round in shape,uniform in size and rough in surface,and the pH-sensitive polymer GMA-AA was grafted to the surface of MSNs,the particle size is distributed in the range of 210-250 nm.The results of BET,FTIR and TGA also showed that the pH-sensitive polymer was successfully grafted（grafting rate of 22.8%）and EB was successfully loaded into MSNs（drug loading of 33.6%）.Release behavior studies showed that higher pH（pH=9）were favorable for EB release.The contact angle of EB@MSNs@K（GMA-AA）on corn leaves was less than that of EB@MSNs on corn leaves,indicating that EB@MSNs@K（GMA-AA）had better spread properties on corn leaves.Both commercial EB@EC and EB@MSNs@K（GMA-AA）,had reasonable control effect against S.frugiperda at the same concentration,but the insecticidal effect of EB@EC was lower than that of EB@MSNs@K（GMA-AA）with time extension,indicating that EB@MSNs@K（GMA-AA）had a longer effective duration（14 d）.The biosafety test showed that the LC50of EB@MSNs@K（GMA-AA）was 20.15 mg/kg at 14 d on earthworms,which showed low toxicity.In addition,EB@MSNs@K（GMA-AA）had no significant effect on the changes in chlorophyll content of corn leaves at a range of concentrations.（3）α-amylase-responsive EB controlled release formulation（EB@MSNs@S（α-CD））was prepared by sol-gel method and surface modification,and microscopic morphology observation showed that the unloaded particles MSNs@S（α-CD）were round in shape,uniform in size and rough in surface,and the thermosensitive polymer NIPAAM-MAA was grafted to the surface of MSNs,the particle size is distributed in the range of 190-230 nm.The results of BET,FTIR and TGA also showed that the α-CD was successfully grafted（grafting rate of 15.1%）and EB was successfully loaded into MSNs（drug loading of 35.9%）.Release behavior studies showed that α-amylase in the system were favorable for EB release.The contact angle of EB@MSNs@S（α-CD）on corn leaves was less than that of EB@MSNs on corn leaves,indicating that EB@MSNs@S（α-CD）had better spread properties on corn leaves.Both commercial EB@EC and EB@MSNs@S（α-CD）,had reasonable control effect against S.frugiperda at the same concentration,but the insecticidal effect of EB@EC was lower than that of EB@MSNs@S（α-CD）with time extension,indicating that EB@MSNs@S（α-CD）had a longer effective duration（14 d）.The biosafety test showed that the LC50 of EB@MSNs@S（α-CD）was 23.89 mg/kg at 14 d on earthworms,which showed low toxicity.In addition,EB@MSNs@S（α-CD）had no significant effect on the changes in chlorophyll content of corn leaves at a range of concentrations.