Biofabrication of silver nanoparticles using Uncaria tomentosa L.: Insight into characterization, antibacterial activities combined with antibiotics, and effect on Triticum aestivum germination

Herein, we used the aqueous extract of Uncaria tomentosa L. barks (Cat’s claw bark [CCb]) for the biofabrication of silver nanoparticles (CCb-Ag-NPs). The effects of different parameters (Uncaria tomentosa L. aqueous extract, silver nitrate [AgNO3] ratio, temperature, and pH) on the formation of the nanoparticles were investigated using UV scan as a preliminary tool for the detection of surface plasmon resonance of CCb-Ag-NPs. The optimal ratio was 1:7 (Uncaria tomentosa L. extract: 1 mM AgNO3 solution). Fourier-transform infrared spectroscopy revealed the functional groups of both CCb extract and the CCb-Ag-NPs, whose dispersion and quasispherical morphologies were characterized using scanning electron microscopy and transmission electron microscopy. Particle sizes ranged from 19.2 to 38.5 nm. The zeta potential of CCb-Ag-NPs was −34.44 mV. According to energy-dispersive X-ray analysis, the CCb-Ag-NPs contained 28.87% silver. The formation of Ag-NPs was also confirmed by X-ray diffraction pattern analysis. Pristine CCb-Ag-NPs showed antibacterial activity against three pathogenic bacterial strains: Escherichia coli (ATCC 25922), E. coli (ATCC 8739), and Pseudomonas aeruginosa (ATCC 90274). Antibacterial activity increased significantly after loading CCb-Ag-NPs on antibiotic discs containing meropenem and cefoxitin. Low concentrations of CCb-Ag-NPs also enhanced the germination percentage, coleoptile length, and radical root length of Triticum aestivum.