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

Silver nanoparticles (AgNPs) have attracted considerable attention due to their remarkable antimicrobial and antioxidant properties. In this study, AgNPs were synthesized through a green and sustainable approach using Adenosma caeruleum R.Br. extract as both reducing and stabilizing agents. The effects of key synthesis parameters, including AgNO₃ concentration, extract to precursor ratio, temperature, pH, and reaction time, were systematically optimized to achieve efficient nanoparticle formation. Comprehensive characterization using UV-Vis, FT-IR, XRD, DLS, zeta potential, TEM, and EDS analyses confirmed the successful synthesis of predominantly spherical and crystalline AgNPs with particle sizes mainly ranging from 20 to 50 nm and a Zaverage hydrodynamic diameter of 47.5 ± 1.4 nm. Despite a relatively broad particle size distribution, the nanoparticles exhibited good colloidal stability, as evidenced by a highly negative zeta potential (- 75.2 ± 1.3 mV). The biosynthesized AgNPs demonstrated notable antioxidant activity against ABTS radicals, with an IC₅₀ value of 49.8 ± 0.14 µg/mL. In addition, significant antimicrobial activity was observed against both bacterial and fungal strains. At a dose of 30 µL, inhibition zones of 21.0 ± 0.18 mm (Escherichia coli), 14.0 ± 0.13 mm (Bacillus cereus), 22.0 ± 0.17 mm (Salmonella typhimurium), 14.0 ± 0.19 mm (Staphylococcus aureus), and 12.0 ± 0.12 mm (Candida albicans) were recorded, with Gram-negative bacteria generally exhibiting greater susceptibility. The minimum inhibitory concentration (MIC) was determined to be 1.25 mg/mL for all tested microorganisms. Overall, the results demonstrate that A. caeruleum-mediated AgNPs possess antibacterial, antifungal, and antioxidant activities and highlight the potential of this indigenous medicinal plant as a sustainable resource for the green synthesis of functional nanomaterials with prospective biomedical and environmental applications.