Green Synthesis of Gold and Copper Nanoparticles by Lannea discolor: Characterization and Antibacterial Activity

Green synthesis using plant extracts has emerged as an eco-friendly, clean, and viable alternative to chemical and physical approaches. Herein, the leaf, stem, and root extracts of Lannea discolor were utilized as a reducing and stabilizing agent in synthesizing gold (AuNPs) and copper (CuNPs) nanoparticles. The formation of AuNPs and CuNPs, confirmed by their color change, was characterized by UV-Vis spectroscopy (UV-Vis), scanning electron microscopy analysis, and energy-dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR), coupled with minimum inhibitory concentration (MIC) antibacterial assays. Gold nanoflowers (AuNFs), NPs, and CuNPs peaked at wavelengths of 316, 544, and 564 nm, respectively. TEM showed unexpected nanoflowers (30–97 nm) in the leaf extracts and spherical NPs (10–33 nm; 9.3–37.5) from stem and root extracts, while spherical CuNPs (20–104 nm) were observed from all the extracts. EDX confirmed the presence of metal salts, and FTIR revealed stable capping agents. AuNPs and NFs from L. discolor extracts showed appreciable antibacterial activity against Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumoniae (ATCC 700603), and Bacillus subtilis (ATCC 6633) when compared to the plant extracts. At the same time, none was observed from the CuNPs. These AuNPs and CuNPs are particularly appealing in various biomedical and conductivity manufacturing applications due to their shapes and sizes and economical and environmentally friendly production. To our knowledge, this is the first study of the synthesis of gold and copper nanoparticles from L. discolor.