Sustainable and eco-friendly synthesis of zinc oxide nanoparticles using <i>Kleinia longiflora</i> and their antibacterial and antioxidant activities

Abstract Zinc oxide nanoparticles (ZnO-NPs) are highly versatile materials with a broad range of applications, including nanomedicine, environmental remediation, cancer therapy, and drug delivery. However, conventional synthesis methods for ZnO-NPs often rely on hazardous chemicals, high energy consumption, and costly procedures, which limit their sustainability, biocompatibility, and large-scale biomedical applicability. Furthermore, there is a critical need to develop eco-friendly synthetic routes that produce nanoparticles with enhanced, tunable antibacterial and antioxidant activity against clinically relevant pathogens. This study reports the synthesis of ZnO-NPs using Kleinia longiflora extracts and zinc nitrate hexahydrate in volume ratios of 1:1, 1:2, and 1:3, yielding ZnO 11 , ZnO 12 , and ZnO 13 nanoparticles, respectively. X-ray diffraction analysis confirmed their hexagonal wurtzite crystal structure, while transmission electron microscopy revealed spherical morphology with average particle sizes of 15.67 nm, 21.59 nm, and 26.92 nm for ZnO 11 , ZnO 12 , and ZnO 13 , respectively. The nanoparticles exhibited ultraviolet-visible absorption peaks between 360 and 376 nm. Antibacterial tests against Gram-positive bacteria ( Staphylococcus aureus and Listeria monocytogenes ) and Gram-negative bacteria ( Escherichia coli and Salmonella enterica ) demonstrated greater efficacy against Gram-positive strains. The anti- S. aureus activity ranged from 0.195 to 1.56 mg ml −1 and was significantly affected ( P &lt; 0.05) by the ZnO-NPs concentration prepared with varying extract volumes. ZnO 11 and ZnO 12 showed comparable antibacterial effects against S. aureus ( P &gt; 0.05), with ZnO 11 achieving the lowest minimum inhibitory concentration of 0.39 mg ml −1 against L. monocytogenes ( P &lt; 0.05). Additionally, antioxidant activity, assessed via the 1, 1-diphenyl-2-picrylhydrazyl assay, showed ZnO 12 had the highest inhibition (69.63%) and lowest IC 50 (32.44 µ g ml −1 ), outperforming other nanoparticle formulations (ZnO 11 and ZnO 13 ). In conclusion, the plant-mediated synthesis of ZnO-NPs generated nanoparticles with robust antioxidant and antibacterial properties, underscoring their promising potential for biomedical applications.