Characterisation, Antibacterial Activity and In Vitro Anticancer Evaluation

The green synthesis of zinc oxide nanoparticles (ZnO NPs) using plant-based reducing and capping agents has gained significant scientific attention as a sustainable and low-toxicity alternative to conventional chemical and physical synthesis routes. This study reports the synthesis of ZnO NPs using aqueous leaf extract of Azadirachta indica (neem), a medicinally important plant whose phytochemical constituents — including nimbidin, azadirachtin, quercetin, and rutin — serve as natural reducing and stabilising agents during nanoparticle formation. The synthesised ZnO NPs were characterised using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), ultraviolet-visible spectroscopy (UV-Vis), and scanning electron microscopy (SEM) to confirm their crystalline structure, surface chemistry, particle size, optical properties, and morphology. XRD analysis confirmed the wurtzite hexagonal crystal structure with crystallite size of 38.4 nm (Scherrer equation), and DLS particle size distribution indicated a mean hydrodynamic diameter of 42.1 nm with polydispersity index of 0.21. Antibacterial activity was evaluated against five pathogenic organisms — Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Bacillus subtilis — by disc diffusion and minimum inhibitory concentration (MIC) assays. The highest zone of inhibition of 20.1 mm was recorded against S. aureus at 400 µg/mL. In vitro anticancer activity assessed by MTT assay against HepG2, MCF-7, and HeLa cell lines revealed IC₅₀ values of 178.4, 112.6, and 98.3 µg/mL respectively, with reactive oxygen species (ROS) generation confirmed as the primary cytotoxic mechanism. The results establish the synthesised ZnO NPs as promising multi-functional nanomaterials with both antibacterial and anticancer applications.