Evaluation of the Antibacterial and Anticancer Properties of Green Zinc Oxide Nanoparticles Synthesized from Spent Camellia Sinensis (Tea) Leaves

Plant-based food waste contains high concentrations of phytochemicals, rendering it an appealing candidate for the eco-friendly production of metal nanoparticles. In this study, zinc oxide nanoparticles (ZnO NPs) were prepared from spent C. sinensis (tea) leaves, serving as both a reducing and a stabilizing agent. Zinc acetate dihydrate [(CH₃COO)₂Zn × 2H₂O] was used as a precursor in the spent C. sinensis leaf extracts for the NPs synthesis. The physicochemical characterization of ZnO NPs was characterized using ultraviolet–visible spectroscopy (UV-VIS), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrophotometer (EDX), X-ray diffraction (XRD), photoluminescence spectroscopy (PL), and dynamic light scattering (DLS). The synthesized ZnO NPs displayed a strong UV–Vis absorption peak at 370 nm, and a wurtzite hexagonal structure with an average crystalline size of 56 nm, as confirmed by XRD. The FESEM confirmed a spherical morphology, while EDX analysis indicated zinc as the predominant element, followed by oxygen. The antibacterial efficacy of ZnO NPs was assessed against both Gram-negative and Gram-positive pathogens, exhibiting optimal effectiveness against Streptococcus pyogenes and Staphylococcus aureus. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay revealed that ZnO NPs exhibited concentration-dependent anticancer activity against HeLa cells, with an IC50 of approximately 33.5 mM. Live–dead imaging confirmed a 4.6-fold and 3.5-fold increase in dead cells at IC50 concentrations after 24 and 48 h, respectively. Furthermore, treatment with ZnO NPs significantly elevated reactive oxygen species (ROS) production, indicating that their cytotoxicity is mediated through ROS generation and its lethal effects. Our findings suggest that ZnO NPs made from spent C. sinensis leaf extracts could have antibacterial and anticancer properties.

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