Eucalyptus globulus and Salvia officinalis Extracts Mediated Green Synthesis of Silver Nanoparticles and Their Application as an Antioxidant and Antimicrobial Agent

Silver nanoparticles (AgNPs) biosynthesized using plant extracts as reducing and capping agents show multiple possibilities for solving various biological problems. The aim of this study was to expand the boundaries of AgNPs using a novel low toxicity and production cost phytochemical method for the biosynthesis of nanoparticles from Eucalyptus globulus and Salvia officinalis aqueous leaf extracts. Biosynthesized AgNPs were characterized by various methods (ultraviolet-visible spectroscopy (UV-vis), Fourier transform infrared (FTIR) spectroscopy with horizontal attenuated total reflectance (HART), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS)). The determined antioxidative and antimicrobial activity of plant extracts was compared with the activity of the AgNPs. The UV-vis spectral analysis demonstrated the absorption peaks at 408 and 438 nm, which confirmed the synthesis of stable AgNPs from E. globulus and S. officinalis, respectively. FTIR-HART results suggested strong capping of phytochemicals on AgNPs. TEM results show mainly spherical-shaped AgNPs, whose size distribution depends on the plant leaf extract type; the smaller AgNPs were obtained with E. globulus extract (with size range of 17.5 ± 5.89 nm compared to 34.3 ± 7.76 nm from S. officinalis AgNPs). The in vitro antioxidant activity evaluated by radical scavenging assays and the reduction activity method clearly demonstrated that both the plant extracts and AgNPs showed prominent antioxidant properties. In addition, AgNPs show much stronger antimicrobial activity against broad spectrum of Gram-negative and Gram-positive bacteria strains than the plant extracts used for their synthesis.