Pyridoxal 5'-phosphate (PLP)-crosslinked chitosan nanogels for pH-responsive pesticide release and enhanced foliar delivery.

Conventional pesticide formulations suffer from poor targeting and low active ingredient utilization due to their inability to respond to microenvironmental signals at pest feeding sites. Here, we developed pH-responsive nanogels by crosslinking chitosan with PLP via Schiff base formation and electrostatic interactions using an inverse emulsion method, and loaded them with the neonicotinoid insecticide thiamethoxam (TMX). The resulting TMX@CS-PLP nanogels exhibited spherical morphology with a hydrodynamic diameter of 428.1 nm, a loading capacity of 9.2%, and an encapsulation efficiency of 79.4%. The Schiff base crosslinks imparted pH-dependent degradability: at acidic pH (5.0, simulating pest gut or infection sites), the nanogels released 88.5% of encapsulated TMX over 72 h, whereas only 23.5% was released at neutral pH (7.0, mimicking leaf surface conditions). The nanogel formulation also improved foliar wettability (contact angle reduced from 84.5o to 68.1o) and enhanced rainfastness compared with the technical suspension. In laboratory bioassays against Myzus persicae, TMX@CS-PLP nanogels caused 76.0% mortality after 24 h, significantly higher than the technical suspension (46.7%), while the blank nanogel showed no phytotoxicity or inherent insecticidal activity. These results demonstrate that PLP-crosslinked chitosan nanogels offer a biocompatible, pH-responsive platform for precision pesticide delivery, with enhanced foliar deposition and improved efficacy.