Green synthesis of Bb-ZnO NPs using Barleria buxifolia leaf extract: Investigations into their physicochemical, biological and anti-cancer properties

Abstract

The plant Barleria buxifolia (Bb) has long been recognized for its medicinal properties. This study investigates the green synthesis of zinc oxide nanoparticles (ZnO NPs) using leaf extracts of B. buxifolia. The aqueous extracts serve as both reducing and stabilizing agents, facilitating a simple, one-step, eco-friendly, and cost-effective synthesis process. The formation of ZnO NPs was validated by the UV–visible absorbance of the surface resonance band at 340 nm. The size of resulting Bb-ZnO NPs was confirmed by TEM. Elemental mapping and stability of NPs were done by using EDS and zeta potential analysis. FTIR was used to characterize of capping agents of the leaf extract, Zeta potential analysis, revealing high stability, crystalline structure, and spherical morphology with sizes ranging from 2 to 50 nm. Furthermore, the synthesized Bb-ZnO NPs demonstrated significant antioxidant activities, as indicated by ABTS, DPPH, and NO assays with IC₅₀ values 67.08 ± 1.42, 62.54 ± 1.38, and 92.63 ± 1.05. The Bb-ZnO NPs exhibited strong antibacterial effects against both Gram-positive (S. aureus) and Gram-negative (E. coli, and P. aeruginosa) bacteria (DIZ of 23.31 ± 1.42 mm, 20.17 ± 1.08 mm, 16.46 ± 1.03 mm for E. coli, P. aeruginosa, and S. aureus are respectively). The anticancer properties of Bb-ZnO NPs, in combination with cisplatin, were evaluated against A549 lung cancer cells, revealing a dose-dependent cytotoxicity while maintaining biocompatibility with normal L929 cells, as confirmed by the MTT assay. The inhibitory concentrations (IC₅₀) were found to be 67.2 µg/mL for Bb-ZnO NPs and 43.5 µg/mL for cisplatin. Anticancer effects were further validated through live/dead (Ao/EtBr), DAPI, ROS, and Rho123 assays. These findings suggest that B. buxifolia extract-mediated ZnO nanoparticles hold potential as therapeutic agents for various human diseases, including lung cancer.