Green synthesis and characterization of nickel oxide nanoparticles using Salvia Officinalis L. extract: Antibacterial activity against ESBL pathogens, antioxidant, and cytotoxicity evaluation

Background: This study aims to biosynthesize nickel oxide nanoparticles (NiO-NPs) using an aqueous extract of Salvia officinalis leaves and to evaluate their antimicrobial, antioxidant, and cytotoxic activities. Methods: The formation of NiO-NPs was confirmed by UV–visible spectroscopy, which revealed a distinct absorption peak at 320 nm. Results: High-resolution transmission electron microscopy (HR-TEM) showed that the nanoparticles were primarily spherical, with an average diameter of 43 ± 16 nm. X-ray diffraction (XRD) analysis verified the crystalline nature of the NiO-NPs, with an estimated crystallite size of 43.53 nm based on the Debye–Scherrer equation. The rising prevalence of antibiotic resistance among ESBL pathogens poses a global threat to public health. Escherichia coli and Klebsiella pneumoniae are among the most common Enterobacteriaceae members that produce extended-spectrum β-lactamase (ESBLs) enzymes. The antibacterial activity of the NiO-NPs demonstrated inhibition zones ranging from 25.33 - 31.83 ± mm against ESBL pathogens. Antioxidant activity was assessed using DPPH and ABTS radical scavenging assays, with 50% inhibition (IC₅₀) observed at concentrations of 513.7 µg/ml, which inhibited 58.46 ± 2.24% of the radicals, and 475 µg/ml, which inhibited 59.01 ± 1.32% of the radicals, respectively. Cytotoxicity was assessed using the MTT assay on HepG2 cancer cells, as well as normal VERO and oral epithelial (OEC) cell lines. The NiO-NPs exhibited an IC₅₀ of 42.62 µg/ml against HepG2 cells. In contrast, the IC₅₀ values for VERO and OEC cells were 224.86 µg/ml and 102.81 µg/ml, respectively, indicating selective toxicity toward cancer cells. Conclusion: These findings suggested that the biosynthesized NiO-NPs serve as a promising antimicrobial and anticancer agent with minimal impact on healthy cells, making them suitable for biomedical and pharmacological applications,