Enzyme cum pH dual-responsive controlled release of avermectin from functional polydopamine microcapsules.

Novel enzyme cum pH dual-responsive microcapsule were prepared with an aim to enhance the utilization of pesticides and reduce environmental pollution. The synthetic procedure involved the introduction of urea bonds by forming a covalent bond between isocyanate-functionalized polydopamine (PDA) microcapsules and polyethyleneimine (PEI). The prepared AVM@PDA-IPTS-PEI microcapsules could effectively protect avermectin (AVM) from ultraviolet radiation, and thus decelerate the decomposition rate; the cumulative release showed positive correlations with pH and the urease activity. The AVM release rate was highest at pH 10. At pH 7, the release rate was enhanced after addition of urease, showing improved urease-responsive property under neutral or weak base condition. Especially at pH 7 in presence of urease, the release behavior was in agreement with the Logistic model and able to describe the S-shaped/sigmoidal release profiles, whereas Korsmeyer-Peppas model was better suited in the absence of urease, as the value of K1 was smaller than 0.45, suggesting that the behavior was controlled by Fick's diffusion. AVM@PDA-IPTS-PEI displayed better adhesion property than AVM, and the microcapsule ameliorated foliage wettability. AVM@PDA-IPTS-PEI exhibited the insecticidal property similarly with AVM, which can be used for reducing the applied quantity of pesticides and improving their efficacy.