Biosynthesis, characterization and anti-dengue vector activity of silver nanoparticles prepared from <i>Azadirachta indica</i> and <i>Citrullus colocynthis</i>

Abstract

We report here biosynthesis of silver nanoparticles (AgNPs) using aqueous extracts of (i) <i>Azadirachta indica</i> leaves and (ii) <i>Citrullus colocynthis</i> fruit and their larvicidal activity against <i>Aedes aegypti.</i> The UV-Vis spectroscopy absorption peaks occurred in the range of 412-416 nm for <i>A. indica</i> AgNPs and 416-431 nm for <i>C. colocynthis</i> AgNPs indicating the silver nature of prepared colloidal samples. The scanning electron microscopy examination revealed the spherical morphology of both types of NPs with average size of 17 ± 4 nm (<i>A. indica</i> AgNPs) and 26 ± 5 nm (<i>C. colocynthis</i> AgNPs). The X-ray diffraction pattern confirmed the face-centred cubic (FCC) structure with crystallite size of 11 ± 1 nm (<i>A. indica</i> AgNPs) and 15 ± 1 nm (<i>C. colocynthis</i> AgNPs) while characteristic peaks appearing in Fourier transform infrared spectroscopy analysis indicated the attachment of different biomolecules on AgNPs. The larvicidal activity at different concentrations of synthesized AgNPs (1-20 mg l^-1) and extracts (0.5-1.5%) against <i>Aedes aegypti</i> was examined for 24 h. A concentration-dependent larvicidal potential of both types of AgNPs was observed. The LC₅₀ values were found to be 0.3 and 1.25 mg l^-1 for <i>C. colocynthis</i> AgNPs and <i>A. indica</i> AgNPs, respectively. However, both extracts did not exhibit any notable larvicidal activity.