Green synthesis of AgNP-ligand complexes and their toxicological effects on Nilaparvata lugens

Despite developments in nanotechnology for use in the pharmaceutical field, there is still a need for implementation of this technology in agrochemistry. In this study, silver nanoparticles (AgNPs) were successfully prepared by a facile and an eco-friendly route using two different ligands, 2'-amino-1,1':4',1″-terphenyl-3,3″,5,5″-tetracarboxylic acid (H₄L) and 1,3,6,8-tetrakis (p-benzoic acid)-pyrene (TBAPy), as reducing agents. The physiochemical properties of the as-obtained AgNPs were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The toxicity of H₄L-AgNP and TBAPy-AgNP against the brown planthopper (BPH, Nilaparvata lugens) was also measured.

SEM and TEM analyses demonstrated the formation of quasi-spherical AgNP structures in the presence of H₄L and TBAPy. Insecticidal assays showed that TBAPy is less effective against N. lugens, with a median lethal concentration (LC₅₀) of 810 mg/L, while the toxicity of H₄L increased and their LC₅₀ reached 786 mg/L 168 h posttreatment at a high concentration of 2000 mg/L. H₄L-AgNPs were also highly toxic at a low concentration of 20 mg/L, with LC₅₀ =  ~ 3.9 mg/L 168 h posttreatment, while TBAPy-AgNPs exhibited less toxicity at the same concentration, with LC₅₀ =  ~ 4.6 mg/L.

These results suggest that the synthesized AgNPs using the two ligands may be a safe and cheaper method compared with chemical insecticides for protection of rice plants from pests and has potential as an effective insecticide in the N. lugens pest management program.