Size-controlled biofabrication of silver nanoparticles using the Merremia emarginata leaf extract: Toxicity on Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae) and non-target mosquito predators

Abstract

Mosquito-borne diseases represent a major human and animal health problem in all tropical and subtropical countries worldwide. The synthesis of eco-friendly metal nanoparticles is a fast-growing branch of current nanoscience with a number of biomedical and entomological implications. In this study, we investigated the one-pot synthesis of silver nanoparticles (Ag NPs) using a cheap leaf extract of Merremia emarginata (Convolvulaceae). Bio-reduced Ag NPs were characterized by UV–visible spectrophotometry, Fourier transform infrared spectroscopy, X-ray diffraction analysis, atomic force microscopy, scanning electron microscopy and transmission electron microscopy. SEM, TEM and AFM morphological nanocharacterization showed that this synthesis led to the production of size-controlled Ag NPs, ranging from 25 to 65nm. The acute toxicity of M. emarginata leaf extract and biosynthesized Ag NPs was evaluated against third instar larvae of the malaria vector Anopheles stephensi, the dengue and Zika virus vector Aedes aegypti and the filariasis vector Culex quinquefasciatus. Compared to the leaf aqueous extract, Ag NPs showed higher toxicity against A. stephensi, A. aegypti, and C. quinquefasciatus with LC50 values of 8.36, 9.20 and 10.02μg/mL, respectively. M. emarginata-fabricated Ag NPs were found safer to non-target aquatic biocontrol agents Anisops bouvieri, Diplonychus indicus and Gambusia affinis, with LC50 ranging from 415.61 to 25,153.46μg/mL. However, although it has been proven the AgNPs fabricated in the present study are more effective if compared to the crude M. emarginata extract, they still exert some toxicity on biocontrol agents, thus further research is required to produce more eco-friendly formulations for field purposes.