Green synthesis of silver nanoparticles represents the great interest in pharmacology due to their wide range of applications. Silver nanoparticles have characteristic physical, chemical, and biological properties, which have potential applications in nanobiotechnological research. Green synthesis involves the synthesis of non-toxic nanoparticles, with cheap and ecological acceptable synthesis technology, and implies the use of plant extracts as a reducing agent of selected metal salts.

In our research, we used the cosmopolitan plant species A. eupatoria, which is known to be used for medicinal purposes, as well as silver nitrate with known antimicrobial properties. Different reaction conditions were applied for the synthesis of nanoparticles using the extracts of A. eupatoria. Silver nitrate was dissolved in different concentrations (5, 10, and 20mM). The reaction mixtures were stirred on a magnetic stirrer and heated at different temperatures (25 ⁰C and 50 ⁰C) until metal nanoparticles were formed. To modify the pH of the reaction mixture (pH 2, 4, and 6) 0,1M HNO₃ or 0,1M NaOH were used. Visual color change (from light yellow to dark brown) and UV-Vis spectrophotometry were used to observe the production of AgNPs throughout the synthesis.

The UV-Vis absorption spectra of formed nanoparticles were recorded (300–800 nm) and the highest peaks were positioned within 300–375 nm (characteristic peak for AgNPs), suggesting the formation of AgNPs. The best conditions for the highest AgNPs yield production were a 5 mM concentration of AgNO₃, a reaction temperature of 25 ⁰C, pH=4, and a reaction time of 3h for synthesis