Green Synthesis of Silver Nanoparticles Using Piper crocatum Leaf Extract and Their Antibacterial Activity Against Staphylococcus aureus

Silver nanoparticles (AgNPs) were synthesized by a green route using an aqueous infusion of red betel (Piper crocatum Ruiz & Pav.) leaves as the reducing agent. The leaves contain tannins, flavonoids, alkaloids, terpenoids and saponins; their phenolic constituents reduce Ag+ and also have antibacterial activity. Synthesis was carried out at four AgNO3 concentrations (1, 2, 3 and 4 mM) and monitored for six days. UV–Vis spectra showed a surface plasmon resonance (SPR) band with absorption maxima at 420–444 nm. The mean hydrodynamic diameter measured by dynamic light scattering decreased from 238 nm (1 mM) to 102 nm (4 mM) as the AgNO3 concentration increased. Antibacterial activity against Staphylococcus aureus was assessed by disc diffusion, with inhibition zones quantified as area by automated digital image analysis. The net inhibition areas of the AgNPs (24.5–35.6 mm2; equivalent diameters 8.2–9.0 mm) did not differ significantly among AgNO3 concentrations and were smaller than that of the crude extract (141.4 mm2). Piper crocatum leaf extract is therefore an effective, eco-friendly reducing agent for AgNP synthesis, but the antibacterial activity of the resulting colloids was moderate, and their colloidal stability must be improved before an advantage over the extract can be expected.