Green synthesis of Ag-Pd bimetallic nanoparticles and its efficacy against mosquito larvae and non-target organisms

Emerging studies on bimetallic nanoparticles highlight their unique synergistic properties, but their efficacy and toxicity require further validation. Silver-palladium bimetallic nanoparticles (Ag-Pd BNPs), synthesized via eco-friendly biological methods, have demonstrated potential applications in catalysis, sensing, antimicrobial activities etc. However, data on their toxicity against invertebrates remains limited. The current study addresses this gap by presenting the eco-friendly synthesis of Ag-Pd BNPs using a nontoxic aqueous leaf extract of the plant Citrus limon. The synthesized nanoparticles were characterized using various techniques, and their efficacy was evaluated against mosquito larvae and nymphs of damselfly and dragonfly. UV–Vis spectroscopy analysis showed maximum absorption at 300 nm ± 40 nm for the leaf extract, while for Ag-Pd BNPs an absence of a surface plasmon resonance band was observed. FT-IR spectroscopy analysis revealed the involvement of surface functional groups from the leaf extract in nanoparticle synthesis. TEM analysis determined a mean particle size of 21 ± 7 d nm. DLS analysis showed an overall hydrodynamic size of the nanoparticles clusters with a Z-average of 1956 d nm. SEM–EDX analysis verified the presence and purity of the Ag-Pd BNPs in the sample, and XRD results identified the leaf extract-mediated synthesis with distinct peaks obtained for Ag and Pd. The nano-toxicity efficacy of Ag-Pd BNPs revealed significant larval mortality against I, II, III, and IV instar larvae of both Anopheles stephensi and Aedes aegypti mosquito species, at 24 h, 48 h, and 72 h of exposure. The selected LC50 was further selected to study the predation efficiency of the non-target nymphs of damselfly and dragonfly which revealed time-dependent predation dynamics, resulting in high predation rates over specific time intervals. The present study offers significant scientific insights into an eco-friendly synthesis and characterization of Ag-Pd BNPs. Their inherent toxic ability to cause mortality in invertebrates like mosquito larvae underscores the need for caution in their environmental application. However, the absence of mortality among the odonate nymphs suggests the potential use of Ag-Pd BNPs in integrated vector management with optimized concentration. Future research can focus on developing controlled-release formulations to optimize environmental safety and facilitate easier remediation in natural ecosystems.