Synthesis, Characterisation, and Evaluation of the Biological Activities of Medicinal Plants-Based Gold Nanoparticles

Gold nanoparticles (AuNPs) were synthesized using extracts from Spirostachys Africana. The AuNPs were characterised using Ultraviolet-Visible spectrophotometry (UV-Vis), X-ray diffraction (XRD), Dynamic light scattering (DLS), Transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). Their antimicrobial activity was tested against World Health Organization (WHO) bacterial priority pathogens. We also assessed their cytotoxicity, anti-inflammatory, and antioxidant activities. The UV-Vis analysis indicated AuNPs formation with surface plasmon resonance (SPR) peaks at 541. The XRD showed face-centred cubic structures with crystalline sizes ranging from 9 to 10 nm. DLS measurements displayed a monodisperse distribution while TEM showed spheroidal AuNPs with sizes of 6-32 nm. The FTIR identified the hydroxyl, carboxyl, and amine groups, involved in reducing and capping of the Au + ions. Antimicrobial assays demonstrated significant antibacterial effects against S. aureus and P. aeruginosa, with MICs of 0.64 and 1.2 mg/mL respectively. Ethanol extracts-conjugated AuNPs exhibited selective cytotoxicity against MCF-7 cancer cells, compared normal cells with an IC₅₀ of 2.67 mg/mL. These AuNPs significantly decreased NO production, indicating anti-inflammatory potential. Methanol-conjugated AuNPs exhibited good antioxidant activity with an IC50 of 38 μg/mL. AuNPs synthesised from S. africana extracts exhibit promising antibacterial activity against AMR pathogens, as well as significant cytotoxic, anti-inflammatory, and antioxidant activities.