Preparation and Characterization of Zein-Based Nanoparticles via Ring-Opening Reaction and Self-Assembly as Aqueous Nanocarriers for Pesticides

Herein, we prepared and compared two water-soluble amphiphilic zein-based nanocarrier systems with avermectin (AVM) payload to enhance pesticide's water-dispersity, foliage wettability, adhesion, anti-UV, and pH-responsive controlled release property. Ethylene glycol diglycidyl ether (EGDE) and diethanolamine (DEA) were utilized to conjugate with hydrophobic zein via a ring-opening reaction and then encapsulated with AVM via a hydrophobic interaction to fabricate a nanopesticide marked as AVM@Zein-EGDE/DEA. For the sake of further improving the nanocarrier's performance, sodium carboxymethyl cellulose (CMC) was grafted with methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) to form a kind of copolymer CMC-g-P(HEMA-MMA), which was applied to conjugate with Zein-EGDE via a ring-opening reaction. Likewise, another nanopesticide system named AVM@Zein-EGDE/CMC-g-P(HEMA-MMA) was obtained through hydrophobic interactions as well as the electrostatic effect. Various techniques were utilized to confirm chemical interaction, thermal behavior, structural characteristics, and stability. The results showed that AVM encapsulated in Zein-EGDE/CMC-g-P(HEMA-MMA) possessed a larger particle size with an average value of 180-254 nm than AVM loaded in Zein-EGDE/DEA with 144-175 nm but had better stability in aqueous solution. Also, AVM loaded in Zein-EGDE/CMC-g-P(HEMA-MMA) enhanced the encapsulation efficiency, and both of them exhibited excellent pH-responsive sustained release behavior. Besides, the former improved wettability on a cucumber leaf surface and enhanced adhesion ability compared to AVM@Zein-EGDE/DEA because of CMC-g-P(HEMA-MMA) with hydrophobic segments. Similarly, anti-UV performance was also enhanced owing to CMC-g-P(HEMA-MMA) as an additional protective layer. More importantly, the encapsulation of Zein-EGDE/DEA and Zein-EGDE/CMC-g-P(HEMA-MMA) as protective barriers for AVM still retained a similar toxicity level. Overall, we demonstrated the proof of concept for the application of amphiphilic zeinbased nanomaterials as aqueous nanocarriers for hydrophobic pesticides.