One-step supramolecular co-assembly of lignin into micro-/nanospheres for photostable, sustained-release delivery of photosensitive pesticides

Abstract

Conventional pesticide formulations face trade-offs among energy-intensive processing, organic-solvent burdens, and poor photostability. While encapsulation strategies offer a remedy, they are invariably hampered by intricate, multi-step fabrication. Herein, we developed a one-step, low-energy platform to prepare aqueous micro-/nanosphere suspensions through cooperative self-assembly between renewable sodium lignosulfonate (SL) and pesticides, exemplified by emamectin benzoate (EB). EB-loaded spheres (EB@MSs and EB@NSs) form in situ at the water/cyclohexanone interface without pre-fabricated carriers or external crosslinking. Multiscale characterization indicates that electrostatic interactions and hydrogen bonding between SL and EB drive the assembly, yielding well-defined, uniform spheres. Remarkably, after 240 min of UV irradiation, EB@MSs and EB@NSs retain approximately 80% of EB, a four-fold enhancement over conventional emulsifiable concentrate (EC) and suspension concentrate (SC) formulations (∼20%). This excellent photostability stems from the protective lignin-based matrix formed during the one-step assembly. Laboratory and field trials against multiple pests demonstrate high efficacy and extended protection, highlighting the potential of this strategy to reduce pesticide dosage. Under the tested conditions, the formulations also showed improved safety toward representative non-target organisms, including Daphnia magna and the predatory mite Amblyseius cucumeris. The strategy also showed preliminary preparative applicability across multiple photosensitive pesticides, which was further supported by functional validation using abamectin (ABM). Overall, this work provides theoretical guidance and a practical framework for the environmentally friendly, low-energy formulation of representative photosensitive pesticides.