Optimization of surface plasmon resonance in green-synthesized silver nanoparticles using response surface methodology: characterization and antibacterial assessment

Bacterial contamination is a persistent issue in food preservation, medical hygiene, and water purification, necessitating the development of eco-friendly and effective antibacterial solutions. In this context, silver nanoparticles (AgNPs) were biosynthesized using an aqueous extract of Marrubium vulgare L. leaf powder – a plant scarcely explored for nanoparticle synthesis. The process was optimized to enhance surface plasmon resonance (SPR) using a Box–Behnken design based on response surface methodology (RSM), taking into account silver nitrate concentration, extract-to-silver ratio, temperature, and reaction time. The statistical model showed impressive prediction capacity (R 2 > 98 %), which was experimentally validated, with high reproducibility. The biosynthesized AgNPs exhibited a well-defined SPR peak around 440 nm, appearing as spherical, uniformly dispersed particles with an average size of 35.35 ± 12.56 nm. XRD analysis confirmed their crystalline structure, while a zeta potential of −48.5 mV indicated excellent colloidal stability – a finding reinforced through assessments over time, demonstrating that the nanoparticles remain highly stable and easily reproducible. The involvement of plant-derived biomolecules was thoroughly examined, revealing that significant proportions of polyphenols (82.07 %), flavonoids (88 %), and tannins (45.49 %) contributed to nanoparticle reduction and stabilization. The antibacterial activity of the synthesized nanoparticles was tested against both Gram-positive and Gram-negative bacteria, showing effective inhibition with zones ranging from 7.23 ± 0.59 mm to 10.60 ± 0.81 mm. Their consistent performance across different bacterial types highlights their versatility and strong potential as a multifunctional antibacterial solution. Overall, these findings position M. vulgare -based AgNPs as a highly stable, reproducible, and eco-friendly alternative for alleviating bacterial contamination in various applications.