Interfacial Engineering of pH-Responsive Nanocarriers for Enhanced Foliar Deposition and Alkaline-Triggered Release

Interface engineering of stimuli-responsive nanocarriers is essential for controlling delivery processes in complex biological environments. Herein, we report a pH-responsive nanocarrier (CPM) constructed via orthogonal thiol-Michael addition and siloxane condensation, integrating chitosan, poly(ethylene glycol) diacrylate, and (3-mercaptopropyl)trimethoxysilane. This carrier encapsulates avermectin (AVM) via multiple noncovalent interactions, including hydrogen bonding, to form AVM@CPM (ACPM) nanoparticles. These particles are acid-inert but undergo rapid disassembly at pH 9.5─the alkaline midgut environment of Ostrinia furnacalis─due to combined ester hydrolysis and amino deprotonation, leading to enhanced release kinetics. Beyond release control, the PEG interfacial layer modulates droplet impact dynamics on hydrophobic surfaces. High-speed imaging reveals that ACPM suppresses droplet rebound and enhances spreading, with the spreading exponent decreasing from 0.52 for water to 0.36 for 500 μg/mL ACPM. This interfacial pinning effect, combined with hydrogen bonding, improves foliar wettability and rainfastness. The alkaline-triggered release translates into insecticidal activity against O.furnacalis, while nanocarrier encapsulation substantially reduces toxicity to nontarget organisms compared to a commercial formulation. This work demonstrates how interfacial engineering─bridging the hydrophobic surface and the alkaline midgut biological interface within a single nanocarrier─can simultaneously govern release kinetics, droplet deposition dynamics, and biological interactions, providing a mechanistically coherent platform for targeted delivery.