Avermectin Microcapsule Pesticide Delivery Systems Based On Coordination Assembly Of Tannic Acid And Metal Ions

Microcapsule pesticide delivery systems can realize stimuli-responsive release of the pesticide active ingredients,improve the utilization rate of pesticides,reduce agricultural production costs and reduce environmental pollution,and achieve timely,dynamic and precise prevention and control of crop diseases,insects and weeds.Coordination assembly is a method that constructing various self-assemblies using metal ions and organic ligands to form stable supramolecular structures.The method was widely used in the constructions of various drug delivery systems.In this paper,two kinds of pH and photothermally responsive microcapsule pesticide delivery systems AVM@CS@TA-Fe and AVM@MSN@CS@TA-Fe were established.The drug load and encapsulation efficiency of the pesticide delivery systems were determined in this paper.The microcapsule samples were characterized by the methods of the infrared spectroscopy(FTIR),scanning electron microscopy(SEM),transmission electron microscopy(TEM),etc.The slow and controlled-release performance,photothermal conversion performance,UV shielding performance and nematoidal activity of these systems were also studied in this paper.1.AVM@CS@TA-Fe system:Avermectin(AVM)was used as the model drug and the chitosan(CS)as the wall material,to prepare the chitosan mono-shell microcapsule pesticide(AVM@CS).Then,the AVM@CS microcapsule pesticide was used as a matrix,a double-shell AVM@CS@TA-Fe microcapsule pesticide delivery system was constructed by introducing metal complex photothermal layer on the surface of the AVM@CS microcapsule by the coordination assembly of tannic acid(TA)and iron ion.The results showed that the AVM@CS@TA-Fe microcapsules had good particle roundness and rough appearance,the encapsulation efficiency of the microcapsule was 94.17%.The system had good slow-release performance,and the release of the avermectin in the microcapsule was consistent with the core material diffusion and the wall material dissolution mechanism.After coating with chitosan layer and TA-Fe layer,the UV shielding performance of the system was obviously improved.In addition,the system also has excellent photothermal responsive performance,the irradiation using near-infrared light or simulated sunlight could promote the release of pesticides in the system.Under the irradiation of 808 nm,2W/cm~2near-infrared light,the photothermal conversion efficiency(η)of the system was 14.18%.Furthermore,the efficacy study showed that the nematoidal activity of the system against pine wood nematode(PWN)and Aphelenchoides besseyi increased31.16 and 28.20 times,respectively,after 8 h of the LED simulated sunlight irradiation.2.AVM@MSN@CS@TA-Fe System:Avermectin(AVM)was used as the model drug and TEOS as the wall material,the mono-shell microcapsule pesticide(AVM@MSN)coating with silicon dioxide was prepared.Then using AVM@MSN microcapsules as a matrix,coating with chitosan(CS),and coordinating assembly with tannic acid(TA)and iron ions,the metal complex photothermal layer was introduced on the surface of microcapsules to form a multi-shell AVM@MSN@CS@TA-Fe microcapsule pesticide delivery system.The particles of the system were spherical and uniform,and the drug load and encapsulation efficiency were 4.45%and 94.28%,respectively.In this case,the slow-release performance and UV shielding performance of the system could be further improved,and the release of avermectin in the system was also consistent with the core material diffusion and the wall material dissolution mechanism.Under the irradiation of 808nm,2 W/cm~2near-infrared light,the AVM@MSN@CS@TA-Fe system had good photothermal conversion performance and photothermal stability,the photothermal conversion efficiencyηis 19.69%.The AVM@CS@TA-Fe and AVM@MSN@CS@TA-Fe microcapsule pesticide delivery systems constructed in this paper,can achieve controlled-release of the avermectin through light-stimulation or pH-regulation.The application and promotion of these pesticide delivery systems can avoid the ineffective release of pesticides,effectively improve the utilization rate of pesticides,reduce agricultural production costs and reduce environmental pollution.