-mediated silver nanoparticles: A green route to potent antibacterials

Using algae for nanoparticle biosynthesis offers a green, cost-effective alternative to other chemical and physical methods. This study uses the cell-free supernatant of Tetradesmus obliquus. to produce silver nanoparticles (AgNPs) sustainably, achieving notable stability and antimicrobial activity. An initial experimental design was used to optimize the production process to maximize nanoparticle yield. The study examined the effects of key variables, including the ratio of extract to silver nitrate solution, the type of capping agent, and the medium pH. The custom design included 12 experiments with varying values for each variable, and we measured absorbance at 420 nm during both shortand long-term assessments to evaluate yield and stability. The results showed that SDS was the most effective stabilizer, resulting in an eightfold increase in nanoparticle production compared to sodium citrate after 2 weeks. At pH 9, with SDS, a rapid synthesis with maximum production was achieved even at lower AgNO3 concentrations. AgNPs (3.90-10.83 nm average diameter, charge= -23.3 mV) were characterized using Zeta potential, FT-IR, XRD, and TEM. Performing disc diffusion assay, agar plates showed significant inhibition zones against Escherichia coli, Salmonella enterica, and Staphylococcus aureus at concentrations of 25, 50, and 100 mg/mL, respectively. These findings highlight the potential of algal-synthesized AgNPs as effective antimicrobial agents.