Salvia rosmarinus L.-Mediated Synthesis of Silver Nanoparticles: Physicochemical Characterization and In Vitro Evaluation of Antimicrobial Activity and Cytotoxicity

This study describes the biosynthesis of silver nanoparticles (AgNPs) using an aqueous Salvia rosmarinus L. (SRL) extract (Family: Lamiaceae) as a natural source of reducing and capping agents through an easy and green method assisted by blue diode laser irradiation (450 nm, 5 W, 5 min). The formation of rosemary-mediated AgNPs was verified by observing a color change in the solution and the presence of a surface plasmon resonance (SPR) band at 454 nm in the UV–Vis spectrum. XRD and FESEM revealed crystalline silver-containing nanostructures with an average estimated crystallite size of 15.53 ± 3.54 nm and particles with an average size of 34.10 ± 14.15 nm, respectively. The presence of silver was confirmed by EDX, while FTIR analysis suggested that functional groups derived from rosemary may have contributed to the reduction of silver ions (Ag⁺) and/or the capping and stabilization of the nanoparticles. The laser-irradiated AgNPs (IR-AgNPs) inhibited clinical isolates of Candida albicans, Candida lusitaniae and Staphylococcus aureus, with minimum inhibitory concentration (MIC) values of 0.125, 0.0625 and 0.25 mM and maximum inhibition zones of 20.5, 22.0 and 17.8 mm, respectively. Furthermore, MTT analysis revealed higher cytotoxicity against ME-180 cancer cells than against normal HdFn cells, with IC₅₀ values of 131.8 and 198.4 µg/mL, respectively (selectivity index ≈ 1.51). These in vitro results indicate that IR-AgNPs possess antimicrobial activity and moderate selective cytotoxicity; however, because non-irradiated particles and in vivo models were not examined, further studies are required to establish the contribution of laser irradiation and the potential of IR-AgNPs for biomedical applications.