Emulsion-based synchronous pesticide encapsulation and surface modification of mesoporous silica nanoparticles with carboxymethyl chitosan for controlled azoxystrobin release

Controlled pesticide release in response to environmental stimuli is highly desirable for improved efficacy and reduced adverse effects. Recently, mesoporous silica nanoparticles (MSN) have become a dazzling star of nanomaterial members in smart delivery systems. In the present study, amino group-functionalized MSN and carboxymethyl chitosan (CMCS) underwent a coupling reaction to facilely afford CMCS modified MSN (MSN-CMCS) as pesticide carrier. However, the loading content of azoxystrobin (AZOX) into MSN-CMCS was only 3.6%, owing to the sharply decreased specific surface area and pore volume. To address this limitation, a novel strategy of emulsion-based synchronous pesticide encapsulation and surface modification of MSN with CMCS was developed. In this way, a satisfactory loading content (21%) can be achieved without sacrificing the pH responsive release properties controlled by gatekeeper CMCS. AZOX-loaded MSN-CMCS exhibited better fungicidal activity against tomato late blight Phytophthora infestans (P. infestans) than AZOX alone under the same doses of active ingredient applied. Fluorescein isothiocyanate-labelled MSN-CMCS were used to track the uptake and translocation of nanoparticles in the target plants and fungi. This research seeks to develop a novel nanocarrier platform for potential applications of pesticides in sustainable plant protection.