Green-synthesized Plectranthus amboinicus silver nanoparticles with broad-spectrum biological activities

Silver nanoparticles (AgNPs) were biosynthesized in an eco-friendly manner using the leaf extract of Plectranthus amboinicus as reducing and stabilizing agent. The characteristic pale yellow to brownish-purple color transition indicated nanoparticle formation, which was further confirmed by UV–Visible spectroscopy with an absorbance peak at 280 nm. SEM and TEM analysis revealed predominantly spherical AgNPs with sizes ranging 35 nm, while SAED (Selected Area Electron Diffraction) patterns confirmed their polycrystalline nature. XRD analysis exhibited sharp FCC (Face-Centred Cubic) Bragg reflections at 38.12°, 44.28°, 64.43°, and 77.38° and FTIR spectra suggested the involvement of phenolic and flavonoid hydroxyl groups in nanoparticle stabilization. The synthesized AgNPs demonstrated notable antibacterial activity against Staphylococcus aureus (18.6 mm), Staphylococcus epidermidis (20.3 mm), Streptococcus mutans (22.2 mm), Candida albicans (19.4 mm), and Aggregatibacter actinomycetemcomitans (17.1 mm) at 100 µg/mL, with a clear dose-dependent inhibition pattern. Antioxidant activity reached 89.1% at 100 µg/mL (compared with 93.2% for ascorbic acid), while anti-inflammatory inhibition was 93.87% (egg albumin assay) and 91.46% (BSA assay). The brine shrimp lethality assay showed low toxicity at 5–10 µg/mL and larvae mortality at high concentrations (40–80 µg/mL). This work demonstrates the novelty of AgNPs isolated from P. amboinicus in displaying wide- spectrum antimicrobial, antioxidant, and anti-inflammatory potential with low cytotoxicity. Follow-up studies should explore mechanistic pathways and in vivo models for demonstrating clinical relevance and therapeutic value.