Green Synthesis and Characterization of Silver Nanoparticles from Pinus nigra Cones: Antioxidant, Antibacterial, and Synergistic Effects.

Abstract

Silver nanoparticles (AgNPs) were synthesized through a green and sustainable approach using aqueous extracts of immature Pinus nigra cones. Characterization by UV-Vis, FT-IR, SEM-EDS, TEM, and XRD confirmed the formation of spherical nanoparticles (22-40 nm) with a face-centered cubic crystalline structure and a characteristic surface plasmon resonance peak at 443 nm. GC-MS analysis of pine cone essential oil identified β-caryophyllene (42.1%) as the major constituent, a compound known for its efflux pump inhibitory properties that may contribute to enhanced antibacterial synergy. Antioxidant assays revealed that the pine cone extract exhibited higher reducing and metal-chelating activities than KAgNPs, whereas the nanoparticles showed moderate radical scavenging activity. Antibacterial evaluations demonstrated that KAgNPs were more effective than the extract, exhibiting lower minimum inhibitory concentration (MIC) values against the tested bacteria, with MICs as low as 0.105 mg/200 µL. Furthermore, synergistic effects were observed when KAgNPs were combined with ofloxacin against Escherichia coli and with daptomycin against Streptococcus mutans. This study represents the first report of AgNP synthesis from immature Pinus nigra cones and highlights their potential as sustainable antioxidant and antimicrobial agents.