pH-responsive mesoporous silica nanoparticles from rice husk ash for delivering trypsin inhibitor to control cotton bollworm

Abstract

The increasing demand for sustainable pest management strategies has driven research into bio-based nanocarriers for pesticide delivery. Mesoporous silica nanoparticles are a type of attractive nano-systems for pesticide delivery; however, they have been synthesized predominantly from non-renewable resources. In this study, mesoporous silica nanoparticles were synthesized from renewable, low-cost rice husk ash, and further functionalized for delivering soybean trypsin inhibitor, a protein bioinsecticide targeting cotton bollworm (Helicoverpa armigera). Functionalization of rice husk ash-derived mesoporous silica nanoparticles by polyethyleneimine enhanced electrostatic interactions and improved adsorption of trypsin inhibitor by 28.1 % compared with bare mesoporous silica nanoparticles. The modification of silica nanoparticles was also confirmed by ²⁹Si and ¹³C nuclear magnetic resonance analyses. Polyethyleneimine functionalization also improved foliar distribution and retention following a simulated rainwash, which was confirmed by confocal microscopy analysis. Controlled release studies revealed mesoporous silica nanoparticles were stable at pH 7 and released trypsin inhibitor at pH above 8, mimicking the midgut conditions of cotton bollworm. In-vivo bioassay results showed that soybean trypsin inhibitor-loaded on amino-functionalized silica nanoparticles reduced larval weight by 81 %, due to the synergistic insecticidal efficacy from trypsin inhibitor and the amino-functionalized silica nanoparticles. This effect likely resulted from the protection of trypsin inhibitor by amino-functionalized nanoparticles silica nanoparticles and amplified insecticidal action, attributed to the combination of physical interactions with the larval gut environment and the enhanced biochemical inhibition of digestive enzymes. This study advanced sustainable pest management strategies based on the use of renewable rice husk ash-derived mesoporous silica nanoparticles for bioinsecticide delivery.