Enzyme/pH-Responsive Sustained Pesticide Release And Performance Evaluation Based On Mesoporous Silica Nanoparticles

Mesoporous silica nanoparticle（MSN）is a non-toxic material with good thermal stability and hydrothermal stability.It contains a large number of silanol groups that can be easily modified and also has a large specific surface with the adjustable pore size range,which can load various drugs to prepare environment-responsive sustained-release pesticide formulations.The environmental responsiveness is an option that can improve the sustained-release performance of pesticides and the materials can deliver the active substance in a controlled and adjustable way under specific environmental conditions,such as pH,enzyme,redox,temperature,and ultrasonic triggering,etc.The nano-pesticide sustained-release system can have a sensitive response to the active substances from the outside world,the plant and pests,so that the pests can be controlled effectively.Among the systems,the research on enzyme response in pesticides is few,so the application of enzyme response in pesticide release is the direction of the paper.This thesis is mainly divided into three parts.Using functionalized mesoporous silica nanoparticles（MSN）as carriers and avermectin（AVM）as a model drug,drug-loaded microspheres with urease,cellulase,and protease responses were designed respectively.And systematically examine the morphology and structure and the various properties,to improve the sustained-release,UV stability,adhesion,wettability,storage dispersion and stability,and insecticidal activity performances of materials.（1）Urea-based functionalized drug-loaded mesoporous silica nanoparticles,CLAVM-MSN-IS-PEI600 and CLAVM-MSN-IS-PEI1800,were obtained by the MSN,which was modified with isocyanate silane coupling agent（MSN-IS）,loaded with AVM（AVM-MSN-IS）and grafted PEI.The materials have spherical morphology and central radial channel arrangement with the reducing of the specific surface area oeing to the modification.The drug loading capacity of MSN increased from 114.4 mg/g（AVM-MSN）to 131.6 mg/g（AVM-MSN-IS）,because isocyanate groups enhanced the hydrogen bonding effect of MSN.CLAVM-MSN-IS-PEI600 and CLAVM-MSN-IS-PEI1800 both have stimulus response to pH.Among them,CLAVM-MSN-IS-PEI600 has obvious responsiveness to urease.Under the different urease concentrations,CLAVM-MSN-IS-PEI600 under the conditions of 1 mg/mL urease solution has the best responsiveness,reaching 64.3%of the release amount at 316 h,while the amount was only11.7%in the environment without urease added.Kinetic studies showed that the release curve at a concentration of 1 mg/mL fitted the Logistic model and can be described as an S-shaped/sigmoidal dissolution release profiles.（2）Cellulose-based functionalized drug-loaded MSN,CLAVM-MSN-NH-EMC,were obtained by the amino-functionalized mesoposous silica（MSN-NH₂）after adsorption of avermectin and grafting of EMC.The loading capacity of AVM-MSN-NH₂ was 232.5 mg/g,which was significantly higher than that of AVM-MSN.CLAVM-MSN-NH-EMC has a stimulus response to pH and cellulose.Under different concentrations of cellulase,the release amount at 2 mg/mL was significantly highest,reaching 53.1%at 310 h,different from 7.4%in the environment without cellulase added.Kinetic studies showed that the release curve at 2 mg/mL fitted the Korsmeyer-Peppas model and controlled by non-Fick diffusion due to the K₂ value larger than 0.45 and smaller than 0.89.（3）Protein-based functionalized drug-loaded MSN,CLAVM-MSN-SS-Zein,were obtained by the sulfhydrylization mesoposous silica（MSN-SH）after adsorption of avermectin and modifing of Zein.The loading capacity of AVM-MSN-SH was 196.4 mg/g.CLAVM-MSN-SS-Zein has a stimulus response to pH and neutral protease.Under different concentrations of enzyme,the release amount at 1,2,and 5 mg/mL was reached from25.0%to 39.3,41.8,and 54.4%,respectively,at 360 h.Kinetic studies showed that the release curves were consistent with the Korsmeyer-Peppas model,and controlled by Fick diffusion since the values of K₂ were smaller than 0.45.（4）UV light stability test showed that the different modified drug-loaded microspheres can effectively improve the ultraviolet shielding effect of AVM.Compared with bare AVM,CLAVM-MSN-IS-PEI,CLAVM-MSN-NH-EMC,and CLAVM-MSN-SS-Zein have better adhesion property.Functionalized drug-loaded MSN has better wettability to foliar surface and good storage dispersibility and stability.It was known from the insecticide experiments that there was no significant difference between the different kind of the Functionalized drug-loaded MSN and the bare AVM.