Laboratory analysis of Au–Pd bimetallic nanoparticles synthesized with Citrus limon leaf extract and its efficacy on mosquito larvae and non-target organisms

The current study provides novel results on the synthesis of bimetallic nanoparticles (BNPs) of gold and palladium (Au–Pd) with an eco-friendly and non-toxic aqueous leaf extract of plant Citrus limon. The BNPs were characterized and toxicity bioassay was examined on the larvae of the pathogen vectors such as Anopheles stephensi and Aedes aegypti mosquitoes. The predation efficiency test was evaluated on the invertebrate non-target organisms such as natural predatory nymphs of dragonfly and damselfly. The results of material characterization using UV VIS spectroscopy confirmed the synthesis of Au–Pd BNPs with the appearance of the SPR bands. FT-IR spectroscopy indicates the presence of functional groups containing high amounts of nitro compounds and amines on the surface of BNPs. TEM result shows the presence of spherical polydisperse Au–Pd BNPs in the sample. The XRD pattern displayed the semi-crystalline nature and the changes in the hydrodynamic size and surface potential was determined for the sample at 0 h, 24 h, 48 h, and 72 h of synthesis through DLS and ZP analysis. Au–Pd BNPs Bioassay provided the effective lethal concentrations (LC(50)) against the I–IV instar larvae of An. stephensi and Ae. aegypti after 24 h, 48 h, and 72 h of exposure. The LC(50) obtained from the larvicidal bioassay was used to test its effect on the predation efficiency of the selected nymphs which showed increased predation from 40 to 48 h of exposure as compared to the negative control. Hereby, we conclude that Au–Pd BNPs bioassay shows toxic mosquito larvicidal activity at the selected concentration with no lethal effect on the predation efficiency of the selected stage of the predatory non-target aquatic invertebrate insects.