Multifunctional positively charged avermectin nanoemulsion fabricated using a cationic polymer emulsifier bearing dual-enzyme cleavable phenyl ester motifs

The development of multifunctional nanopesticides poses considerable challenges, primarily due to issues such as weak adhesion and off-target losses, which typically lead to inefficient utilization. In this study, a novel cationic amphiphilic emulsifier, designated as PEI-PA, was synthesized through an efficient Michael addition reaction between polyethyleneimine and phenyl acrylate, followed by neutralization with acetic acid. Stabilized by PEI-PA, a positively charged avermectin nanoemulsion was fabricated via a phase inversion emulsification process. The resulting optimal avermectin nanoemulsion, referred to as AVM@PEI-PA, exhibited desired properties including small particle size (93.1 ± 2.2 nm), high encapsulation efficiency (82.55 ± 0.56 %), and robust stability against shearing, storage, and UV irradiation. In comparison to the avermectin emulsifiable concentrate, AVM@PEI-PA demonstrated superior spreadability, reduced splash and bounce on hydrophobic cabbage leaves attributed to its lower surface tension, smaller contact angle, and enhanced thixotropy. Notably, the particles of AVM@PEI-PA were effective in bidirectional translocation between cabbage leaves and roots, especially from leaves to roots. More crucially, the stability of the nanoparticles was compromised under various stimuli, such as pH, temperature, esterase, glutathione, and ursolic acid, either individually or in combination, facilitating the release of avermectin molecules. Interestingly, the nanoparticles exhibited obvious esterase/glutathione dual-responsiveness due to the hydrolysis and thiolysis of the phenyl ester in PEI-PA, and this responsiveness could be regulated by the other stimuli (pH, temperature, and ursolic acid). This work highlights the significance of advanced polymer emulsifiers tailored to specific application requirements, presenting a key step forward in the development of intelligent, multifunctional delivery systems for agricultural applications.