Thermoresponsive polymer-encapsulated hollow mesoporous silica nanoparticles and their application in insecticide delivery

Improving pesticide efficacy, which depends on the smart delivery of pesticides in the field, has been the basis for reducing the use of agricultural chemicals to an optimal level. Herein, a temperature-responsive release formulation (THI@HMS@P(NIPAM-MAA)) that can regulate pesticide release based on the relationship between pesticide efficacy and ambient temperature is proposed. The THI@HMS@P(NIPAM-MAA) was prepared by seeded precipitation polymerization, wherein hollow mesoporous silica (HMS) was employed as the core; a commonly used thermoresponsive copolymer, poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-MAA)), was used as the outer shell; and a type of positive temperature coefficient insecticide, thiamethoxam (THI), was selected as the model pesticide. The prepared THI@HMS@P(NIPAM-MAA) can effectively protect THI against degradation under UV irradiation and showed strong adhesion to rice leaves. The bioactivity results showed that the mortality of THI@HMS@P(NIPAM-MAA) against Nilaparvata lugens (Stal) (Hemiptera: Delphacidae) was positively correlated with temperature and mainly benefitted from the temperature-induced variation in the release rate. Furthermore, the THI@HMS@P(NIPAM-MAA) possessed long-term bioactivity (14 days) and showed negligible effects on rice seedling growth. This temperature-responsive release formulation may be extended to other positive temperature coefficient pesticides in the future, thus greatly advancing smart pesticide formulation development.