Construction And Application Of Environmentally Responsive Nano-controlled Release Formulation Of Indoxacarb

Major lepidopteran pests such as Spodoptera frugiperda,Cnaphalocrocis medinalis and Spodoptera litura seriously threaten food security in China.Indoxacarb(IN)has good bioactivity against lepidoptera pests and is recommended by the Ministry of Agriculture and Rural Affairs to control many lepidopteran pests in China.However,traditional IN formulations still exhibit problems,such as high use of organic solvents and emulsifiers,poor environmental compatibility,low utilization of active ingredients and difficulties in precise application.Consequently,the insecticidal efficacy would decrease.It is necessary to increase IN dosage to improve its control effects,easily causing environmental pollution and increasing the cost of pest control.Mesoporous silica nanoparticles(MSNs)have adjustable size,ordered pore channels,large specific surface area and biocompatibility.They are widely used in biopharmaceuticals and are also hot carrier materials for controlled-release pesticides.To address the disadvantages of traditional pesticide formulations,this thesis prepared environmentallyresponsive controlled-release IN nano-agents by modifying MSNs and investigated their bioactivity and biosafety.The main research results are as follows:(1)Hollow MSNs were synthesized by the hard template method and modified by PDA and α-cyclodextrin(CD)to obtain pH and enzyme-responsive controlled-release IN nanoagents(IN@MSNs@PDA@CD).Microscopic morphology reveals that MSNs exhibited a regular spherical core-shell structure with uniform dispersion,and the particle size ranged between 290-310 nm.Mapping,FTIR,BET and TGA results also show that the polymer was successfully grafted(at a grafting rate of 5.3%),and IN was successfully loaded(at a loading rate of 22.5%).Release behavior analysis shows that IN release was accelerated in alkaline environments,and IN@MSNs@PDA@CD release was also significantly accelerated when aamylase was present.Under UV light irradiation,IN@MSNs@PDA@CD provided better protection against IN prodrugs.The bioactivity assay shows that IN@MSNs@PDA@CD had higher bioactivity against Spodoptera frugiperda than commercial IN@EC at the same concentration,and their control effects decreased with time.The biosafety test shows that LC50 values of IN@MSNs@PDA@CD and IN@EC against earthworms at 14 d were 16.64 and 7.16 mg kg-1 soil,indicating low toxicity and moderate toxicity,respectively.LC50 values of IN@MSNs@PDA@CD and IN@EC against zebrafish at 96 h were 14.65 and 1.67 mg L-1,respectively,indicating that IN@MSNs@PDA@CD can reduce the toxicity to zebrafish.(2)MSNs were prepared by the sol-gel method and modified using disulfide bonds and CD to obtain the redox,enzyme-responsive controlled-release nano-agent(IN@MSNs@SS@CD).Microscopic morphological observations show that the nanoparticles were spherical with a rough surface.The surface of MSNs was covered with redox and enzyme-sensitive substances and had a certain core-shell structure.The particle size was concentrated between 161-194 nm.Mapping,FTIR,BET and TGA results also show that the polymer was successfully grafted(17.3%),and IN was successfully loaded(22.3%).Release behavior studies show that IN release was accelerated after the addition of glutathione,and IN@MSNs@SS@CD release was also significantly accelerated when α-amylase was present in the environment.Under UV light irradiation,IN@MSNs@SS@CD provided better protection against IN prodrugs.The bioactivity assay results show that IN@MSNs@SS@CD had higher bioactivity against Cnaphalocrocis medinalis than commercial IN@EC at the same concentration.Although their control effects decreased with time,IN@MSNs@SS@CD still had higher insecticidal activity,indicating that IN@MSNs@SS@CD had a longer insecticidal shelf life(14 d)than commercial IN@EC.The biosafety test shows that LC50 values of IN@MSNs@SS@CD and IN emulsions against earthworms at 14 d were 18.68 and 6.86 mg kg-1 soil,indicating low and moderate toxicity,respectively.LC50 values of IN@MSNs@SS@CD and IN emulsions against zebrafish at 96 h were 22.34 and 1.45 mg L1,respectively,indicating that IN@MSNs@SS@CD can reduce the toxicity to zebrafish.(3)MSNs were prepared by the self-templating method using sodium hydroxide-etched silica colloids and modified with N-isopropylacrylamide(NIPAM)and CD to obtain temperature-and enzyme-responsive controlled-release IN nano-agent(IN@MSNs@NIPAM@CD).Microscopic morphological observations show that the nanoparticles had a spherical core-shell structure with a rough surface and exhibited homogeneity and dispersion.The particle size ranged between 320-330 nm.Mapping,FTIR,BET and TGA results also show that the polymer was successfully grafted(23.2%),and IN was successfully loaded(46.3%).Release behavior studies show that IN release was accelerated at higher ambient temperatures,and IN@MSNs@NIPAM@CD release was significantly accelerated when α-amylase was present.Under UV light irradiation,IN@MSNs@NIPAM@CD provided better protection against IN prodrugs.The bioactivity assay shows that IN@MSNs@NIPAM@CD had higher bioactivity against Spodoptera litura than commercial IN@EC at the same concentration.Although their control effects decreased with time,IN@MSNs@NIPAM@CD still had higher insecticidal activity,indicating that IN@MSNs@NIPAM@CD had a longer insecticidal shelf life(14 d)than commercial IN@EC.The biosafety test shows that IN@MSNs@NIPAM@CD had stronger insecticidal activity than commercial emulsions.LC50 values of IN@MSNs@NIPAM@CD and IN emulsions against earthworms at 14 d were 17.59 and 6.12 mg kg-1 soil,indicating low and moderate toxicity,respectively.Their LC50 values against zebrafish were 18.48 and 1.51 mg L-1,respectively,indicating that IN@MSNs@NIPAM@CD can reduce the toxicity to zebrafish.