Green Synthesis of AgNPs from Celtis africana: Biological and Catalytic Insights

<i>Celtis africana,</i> a rare plant native to southwestern Saudi Arabia, was explored for the first time as a source for the green synthesis of silver nanoparticles (AgNPs). Catechol-bearing phenolic amides in the aqueous leaf extract acted as both reducing and capping agents, enabling eco-friendly AgNP fabrication. The synthesized AgNPs were characterized using SEM, TEM, XRD, UV-Vis, and FTIR, revealing predominantly spherical nanoparticles with an average size of 9.28 ± 0.11 nm, a face-centered cubic crystalline structure, and a pronounced surface plasmon resonance at 424 nm. HPLC analysis confirmed the presence of caffeoyltryamine in the extract, while UV-Vis and FTIR indicated its attachment to the AgNP surface. The AgNPs exhibited broad-spectrum antimicrobial activity against Gram-positive bacteria (<i>S. aureus</i>, MRSA and <i>E. faecalis</i>) and Gram-negative bacteria (<i>E. coli</i>, <i>K. pneumoniae</i>, <i>S. typhimurium</i>, and <i>P. aeruginosa</i>), as well as pathogenic fungi such as <i>C. albicans</i>, <i>C. glabrata</i>, <i>C. parapsilosis</i>, and <i>C. krusei</i> with performance comparable to or exceeding that of AgNPs from <i>Artemisia vulgaris</i>, <i>Moringa oleifera</i>, and <i>Nigella sativa</i>. The MIC and MBC values for <i>S. aureus</i>, MRSA, <i>E. coli</i>, and <i>S. typhimurium</i> were consistently 6.25 µg/mL and 25 µg/mL, respectively, reflecting strong inhibitory and bactericidal effects at low concentrations. MTT assays demonstrated selective cytotoxicity, showing higher viability in normal human skin fibroblasts (HSF) than in MCF-7 breast cancer cells. The AgNPs also displayed strong antioxidant activity (IC₅₀ = 5.41 µg/mL, DPPH assay) and efficient catalytic reduction of 4-nitrophenol (4-NP) and methylene blue (MB), with rate constants of 0.0165 s^-1 and 0.0047 s^-1, respectively, exceeding most reported values. These findings identify <i>Celtis africana</i> as a promising source for eco-friendly AgNPs with strong antimicrobial, antioxidant, and catalytic properties for broad biological and environmental applications.