Biosynthesis of Zinc Oxide Nanoparticles Using Aqueous Leaf Extract of Alternanthera philoxeroides for Antioxidant and Antibacterial Activities

In the contemporary scientific landscape, the demand for sustainable and nontoxic synthesis of metallic nanoparticles has grown significantly, with biological or green synthesis approaches being preferred over conventional physical and chemical methods due to their eco-friendly, cost-effective, and nonhazardous nature. In this study, zinc oxide nanoparticles (ZnONPs) were synthesized via a simple and environmentally benign process using an aqueous leaf extract of Alternanthera philoxeroides as a natural bio-reducing and stabilizing agent, along with zinc acetate as the precursor salt. The formation of A. philoxeroides–mediated ZnONPs was confirmed by a characteristic surface plasmon resonance (SPR) band at 351 nm in the ultraviolet-visible (UV-Vis) spectrum and by energy dispersive X-ray (EDX) analysis showing elemental zinc and oxygen. Fourier transform infrared (FTIR) spectroscopy displayed peaks at 3,397, 2,930, 1,633, 1,408, 1,312, 1,072, 1,025, 821, and 619 cm−1, indicating phytochemicals responsible for reduction and capping. Zeta potential analysis yielded a value of −16.4 mV, reflecting moderate stability. X-ray diffraction (XRD) confirmed the crystalline wurtzite structure, further supported by the selected area electron diffraction (SAED) pattern. Field emission scanning electron microscopy (FESEM) revealed spherical nanoparticles with an average size of 15 nm, and high-resolution transmission electron microscopy (HRTEM) showed a size distribution between 3 and 35 nm with distinct lattice fringes. Antibacterial evaluation using the agar well diffusion method demonstrated the highest inhibition against Staphylococcus aureus, while antioxidant activity assessed by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay exhibited a half-maximal inhibitory concentration (IC50) of 85.42 μg per milliliter (μg/mL), indicating strong radical neutralization capacity. These results highlight the potential of bio-synthesized ZnONPs for diverse biomedical, pharmaceutical, and industrial applications, warranting further investigation into their cytotoxicity, targeted drug delivery potential, and performance in real-world biomedical systems.