Dual-responsive microcapsules with tailorable shells from oppositely charged biopolymers for precise pesticide release

Abstract

Controlled-release systems are effective in improving the utilization efficiency of pesticides. Here, pH/laccase responsive microcapsules with tunable release performances were prepared by the layer-by-layer deposition of sodium lignosulfonate (SL) and chitosan (CH) for protecting photosensitive avermectin (AVM). First, the homogeneity of AVM was improved by recrystallization for the better investigation of its encapsulation and release performance, and this was confirmed by X-ray diffractometry and Fourier-transform infrared spectroscopy characterization. Subsequently, the microcapsules were prepared via a layer-by-layer assembly strategy. It was found that electrostatic interactions rather than chemical reactions were the main driving forces for the formation of the AVM@(CH + SL)n microcapsules. AVM@(CH + SL)n not only had a high encapsulation efficiency (over 90%), but also exhibited outstanding performance in terms of sustained release and antiphotolysis of AVM. As a result, the 80% AVM release time (t₈₀) of AVM@(CH + SL)5 was 197.24 h, which was much higher than that of the commercial formulation (94.20 h). More importantly, AVM@(CH + SL)n was responsive to laccase and pH. The release of AVM from AVM@(CH + SL)5 at an enzyme activity up to 500 U g⁻¹ was increased by 181.02%. Under alkaline conditions, the interaction between CH and SL was weakened, which also greatly enhanced the release of AVM. These results confirmed that laccase and the unique alkaline environment in Lepidopteran pests could act as trigger factors for AVM release by AVM@(CH + SL)n. Overall, the novel pesticide carrier system prepared in this study can realize the precise release of pesticides as well as the high-value utilization of natural biomass resources.