Ultrasound-assisted ionic gelation of neem oil-encapsulated chitosan nanoparticles as a promising biopesticide

Neem oil contains large amounts of azadirachtin, which have excellent antibacterial, antifungal, insecticidal, and pesticidal properties that can protect plants from various agricultural diseases. However, neem oil is hydrophobic and sensitive to environmental conditions, its direct application is limited by dilution, spraying, adhesion, and easy oxidation by components containing unsaturated bonds. Nanochitosan is a carrier system for the limitation of neem oil and is a biopesticide, antibacterial, and antifungal-enhancing agent. In this study, a novel fabrication of neem oil-encapsulated nanochitosan by ultrasound-assisted ionic gelation using sodium tripolyphosphate as a crosslinker. The effects of chitosan-neem oil mass ratios (1:0, 1:0.1, 1:0.25, 1:0.5, 1:0.75, 1:1 g/g) and ultrasonic times (5, 10, 15, 20, 25 min) on the particle size, encapsulation efficiency (EE), and loading capacity (LC) of neem oil loaded nanochitosan (CS/NO NPs) are comprehensively investigated. The CS/NO NPs have a diameter of 132.6–196.3 nm, zeta potential of 8.4–26.1 mV, EE and LC of 87.59–96.10%, and 21.90–24.03%, respectively. Ultrasonic treatment for 20 min is found to be the optimal time for the most stable nanoparticles. Field emission scanning electron microscope images demonstrated that nanochitosan had a spherical shape, whereas CS/NO NPs formed agglomerates with larger particle sizes. X-ray powder diffraction analysis revealed two distinct peaks at 2θ = 13° and 20°, characterized by the highly amorphous structure of CS/NO NPs. Therefore, the combination of neem oil and nanochitosan is a promising biopesticide with bioavailability, nontoxicity, and eco-friendliness for sustainable agriculture.