Green Synthesis of Silver Nanoparticles Using the Extract of Adenosma Caeruleum R.br.: Evaluation of Antibacterial, Antifungal and Antioxidant Activity

Silver nanoparticles (AgNPs) have garnered considerable interest owing to their outstanding antimicrobial and antioxidant performances. In the present work, AgNPs were greenly synthesized using Adenosma caeruleum R.Br. extract, which simultaneously acted as reducing and capping agents, providing an environmentally benign and sustainable route for nanoparticle production. The influence of key synthetic variables, including AgNO₃ concentration, extract-to-precursor ratio, temperature, pH, and reaction time, was systematically optimized to achieve well-dispersed and stable nanostructures. Comprehensive physicochemical characterization by UV–Vis, FT-IR, XRD, DLS, zeta potential, TEM, and EDS confirmed the successful formation of crystalline, predominantly spherical AgNPs with core sizes in the range of 20–50 nm and an average hydrodynamic diameter of ~ 47.5 nm, indicative of good colloidal stability imparted by phytochemical capping layers. The biosynthesized AgNPs exhibited notable radical-scavenging activity toward ABTS•⁺ with an IC ₅₀ value of 49.8 µg mL⁻¹, demonstrating a moderate yet meaningful antioxidant capacity. Significant antimicrobial efficacy was also observed in the agar well diffusion assay (30 µL), producing inhibition zones of 21.0 mm ( Escherichia coli ), 14.0 mm ( Bacillus cereus ), 22.0 mm ( Salmonella typhimurium ), 14.0 mm ( Staphylococcus aureus ), and 12.0 mm ( Candida albicans ), where Gram-negative bacteria were generally more susceptible. The minimum inhibitory concentration was 1.25 mg mL⁻¹ for all tested strains. Overall, these findings demonstrate that A. caeruleum -mediated AgNPs possess promising antibacterial, antifungal, and antioxidant properties, highlighting their strong potential for future biomedical and environmental applications.