Functional polymer micelles based on quaternized polyethyleneimine for efficient delivery of insoluble fungicide with synergistic antimicrobial activity

To mitigate the dependency on toxic auxiliary agents in pesticide formulations and enhance bioactivity, a novel functional polymeric micelle carrier was engineered through the synthesis of graft-modulated, amphiphilic quaternary ammonium polyethyleneimine (QPEI). A series of QPEI polymers were synthesized by conjugating polyethyleneimines (PEIs) of varying molecular weights (600, 1800, and 10,000) with different acyl chlorides (palmitoyl, propionyl, and benzoyl). From this library, pal-QPEI 600 emerged as the optimal candidate to encapsulate the hydrophobic fungicide pyraclostrobin (PYR) for preparation of pesticide-loaded micelles (PYR@QPEI) duo to the highest quaternization degree, the lowest surface tension (35.04 mN/m), and the most potent antimicrobial activity. The resulting PYR@QPEI micelles were spherical and regular nanostructure with loading capacity of 7.02 % and superior interface performance on plant leaves and exhibited pH-responsive release behavior. In both in vitro and in vivo assays, PYR@QPEI showed good antifungal efficacy against Sclerotinia sclerotiorum compared to a commercial PYR suspension concentrate. The synergistic ratio between PYR and QPEI was calculated to be 1.74, confirming a synergistic antimicrobial effect. Furthermore, PYR@QPEI exhibited good storage stability, enhanced photostability, and high safety for plants with no significant genotoxicity. This study presents a smart, effective, and environmentally friendly nanopesticide delivery platform that reduces the need for toxic auxiliaries.