Green synthesis of silver nanoparticles using Catharanthus roseus leaf and stem extracts and their differential antibacterial activity

Silver nanoparticles (AgNPs) synthesized via plant-mediated approaches offer eco-friendly alternatives to conventional antimicrobial agents; however, comparative studies on different plant parts remain limited. In this study, AgNPs were synthesized using aqueous extracts of Catharanthus roseus leaves and stems. Extracts were prepared by boiling 10 g of dried plant material in 100 mL of distilled water, followed by reaction with 1 mM AgNO₃ and incubation for 24 h in the dark. Nanoparticle formation was preliminarily confirmed by visual color change, indicating the reduction of Ag⁺ ions; advanced physicochemical characterization was not performed, and thus the findings represent a preliminary screening study. Antibacterial activity was assessed using the disk diffusion method against Gram-positive (Bacillus subtilis, Staphylococcus aureus) and Gram-negative (Escherichia coli, Salmonella abony) bacteria. Leaf-derived AgNPs exhibited higher antibacterial activity, with a maximum inhibition zone of 16.3 ± 0.7 mm against B. subtilis, compared to 14.5 ± 0.6 mm for stem-derived AgNPs. Gram-negative bacteria showed lower susceptibility, with inhibition zones ≤ 12 mm. These results indicate plant-part-dependent variation in antibacterial activity. However, further studies involving physicochemical characterization, MIC/MBC assays, and phytochemical profiling are necessary to validate and extend these findings.