Construction Of Responsive Nano-loading System By Electrostatic Self-assembly And Its Performance In Insecticide Delivery

Pest control is essential in agricultural production.However,chronic low utilization rate has led poor control effect and drug waste,posing a serious threat to the ecological environment and human health.New technologies are urgently needed to overcome these problems.The application of nanotechnology is expected to improve the utilization rate and insecticidal effect of pesticides.However,although there are many methods to prepare nanopesticides in the laboratory,there are still some problems,such as complex preparation process and difficult degradation of carriers,which restrict their advantages.Therefore,it is urgent to find or develop a new process with simple process and environment-friendly carriers.To address this need,this study firstly evaluated the potential of nanogels in delivering the insecticides and found that electrostatic interaction is critical for the construction of nanoparticles.Then,a nano-loading system with a core-shell structure was constructed using an electrostatic self-assembly method,and the potential of its for delivering the insecticides was examined.The main results are as follows:1.To investigate the feasibility of nanogel as insecticide carriers,polyvinyl alcohol-valine polymers were synthesized.An emamectin benzoate nanogel suspension（EB NS）was prepared by solvent evaporation method using PVA-V as the carrier.EB NS was stable under hot storage,cold storage and room-temperature storage for one year.The retention of EB NS dilutions at a concentration of 10 mg/L on the leaves was about 9%higher than that of emamectin benzoate emulsifiable concentrate（EB EC）.The half-life of EB NS under UV light was 3.3 times longer compared to EB EC.PVA-V and surfactant can form the coacervate covering the nanogels particles after drying of EB NS dilution,and this structure contributes to the photostability of the EB.The bioactivity of the insecticides against larvae of the Plutella xylostella（L.）was determined by the leaf-dip method,and the corrected mortality at 96 h after EB NS treatment was 5-30%higher than that of EB EC in the concentration range of 0.1-2 a.i.mg/L;EB NS also had a longer pest control period in greenhouse trials.2.A nanopesticide system loaded with lambda-cyhalothrin（LC）is established by iron mineralization after electrostatic self-assembly between sodium lignosulphonate（SL）and dodecyl dimethyl benzyl ammonium chloride（DDBAC）.The obtained nanocapsules with a particle mean size of 300 nm have a core-shell structure.Increasing the amount of SL and DDBAC is beneficial to stabilize the capsule shape and reduce the size of nanocapsules,and DDBAC has a greater effect on the size.The infrared spectroscopic detection proves that the electrostatic gravitational force of sulfonic acid groups and quaternary ammonium ions on SL and DDBAC is the driving force of the capsule formation.XPS detection confirmed that the presence of iron on the nanocapsule surface and the phenolic hydroxyl groups in the SL provide sites for the chelation of Fe³⁺.The method is suitable for encapsulating hydrophobic and low volatile insecticides.The loading of nanocarriers prolonged the half-life of LC under UV irradiation by 4.4 times compared to LC emulsifiable concentrate（LC EC）,and the insecticidal activity under UV irradiation was about 2-39%higher than that of LC EC.The alkaline conditions and laccase could promote the release of active ingredients from the carrier of SL/DDBAC/Fe.The nanocarrier SL/DDBAC/Fe has the advantages of a simple preparation process,environmental safety,and dual-response release characteristics,which provides a promising nano platform for pesticide precision delivery.3.LC nanocapsules suspension（LC NS）was prepared using the electrostatic self-assembly method,however,we found that the insecticidal rate and insecticidal activity of this formulation were lower than that of LC EC.Inspired by the biological mechanism that Lepidopteran pests release laccase and polysaccharidase to degrade plant tissues,chitosan（CS）or alkyl polysaccharide quaternary ammonium salt（APQAS）were introduced into lignin-based carriers to prepare LC@SL/CS/Fe and LC@SL/APQAS/Fe.The morphological stability and photostability of LC@SL/APQAS/Fe were superior to LC@SL/CS/Fe,which was associated with more Fe³⁺adsorption on the surface of the former.The encapsulation of nanocarriers SL/CS/Fe and SL/APQAS/Fe prolonged the half-life of LC under UV irradiation by 1.50-and 6.03-fold,respectively.Both LC@SL/CS/Fe and LC@SL/APQAS/Fe showed responsive release properties to laccase and cellulase.The stomach toxicity of LC@SL/CS/Fe and LC@SL/APQAS/Fe at 48 h was comparable to that of LC EC.The persistence studies were conducted in the greenhouse and were performed by periodically picking insecticide-treated cabbage and feeding test worms to demonstrate application performance.The result show that the pest control period of LC@SL/APQAS/Fe was longer than that of LC@SL/CS/Fe and LC EC.The toxicity of LC@SL/APQAS/Fe to ladybug larvae was 2-3 times lower than that of LC@SL/CS/Fe and LC EC.To verify whether nanocapsules can exhibit bioactivity through uptake and conduction by plants,nanopesticides（100-300 nm）were prepared with SL/APQAS/Fe as carriers.It was found that the loading-system could not exhibited bioactivity through corn leaves,corn roots,or cucumber leaves uptake and conduction,in the tested concentration range.Therefore,the nanocapsules suspension developed in this study improve the control efficacy of LC against Lepidopteran pests while improving its safety against natural enemies.And its cost and environmental safety are better than the traditional emulsion.The electrostatic self-assembly method established in this study is a simple process with mild conditions and has potential for industrial production.The delivery system has responsive release performance to laccase and cellulase in Lepidopteran insects,which promotes the precise delivery and the safety of insecticides.Compared with conventional EC preparation,this nano formulation has the advantages of favorable environmental compatibility,low cost,low organic solvent content,and persistent period.This study can promote the application of nano-insecticides and sustainable agricultural development.