Bi-directional pH-responsive cellulose nanocrystals-based pesticide microcapsules for sustainable agriculture

Smart-release pesticide microcapsules have more advantages than traditional pesticide formulations in sustainable agricultural practices. Here, we employed cellulose nanocrystal-based Pickering emulsion (ACNCs-Pickering) as the core material, followed by coating chelating networks consisting of tannic acid (TA) and iron ions (Fe^III). This strategy successfully developed a bi-directional pH-responsive imidacloprid (IMI)-containing microcapsule formulation (IMI@ACNCs@TA-Fe^III) for environmentally friendly and efficient pest control. IMI@ACNCs@TA-Fe^III achieved an encapsulation efficiency of 91.13 % and a drug loading capacity of 17.26 %, respectively. In vitro sustained-release experiments demonstrated that in non-neutral media (i.e., pH = 4 and 10), IMI@ACNCs@TA-Fe^III achieved a cumulative release rate of 86 % within 96 h, which was 1.4-fold of that under neutral conditions. Additionally, experiments using Chinese cabbage (Brassica rapa L. ssp. pekinensis) as the crop model and the Plutella xylostella as the pest model indicated that this system could significantly enhance the foliar adhesion and insecticidal activity of IMI, and also exhibited excellent UV resistance. IMI@ACNCs@TA-Fe^III also had a negligible influence on seed germination, microbial growth, and zebrafish survival, indicating biosafety for non-target organisms. Overall, we combined coordination and Pickering emulsion template routes to fabricate the bi-directional pH-responsive pesticide formulation with remarkable performances, indicating the excellent potential in sustainable agriculture.