Bio‐Mediated Synthesis of CuO Nanoparticle for Antibacterial and Antioxidant Applications via <i>Croton macrostachyus</i> Hochst. Ex Delile Leaf Extract

ABSTRACT The advancement of green technology is a key focus of global research aimed at synthesis of environmentally friendly, cost‐effective, and biocompatible copper oxide nanoparticles. This study involved the synthesis of CuO nanoparticles (CuO NPs) using hydrated copper sulfate as a precursor and Croton macrostachyus Hochst. ex Delile leaf extract as a reducing and capping agent. Characterization of the synthesized CuO NPs was performed using UV–Vis, XRD, and FT‐IR spectroscopy. A noticeable color change from light green to brownish black indicated the formation of nanoparticles. Phytochemical analysis revealed the presence of alkaloids, flavonoids, phenols, tannins, and terpenoids in the leaf extract. The nanoparticles had a crystalline size of 9.53 nm, and SEM images displayed small, spherical structures. The antibacterial efficacy of the CuO NPs was assessed against both Gram‐positive and Gram‐negative bacterial strains through the agar well disc diffusion method, demonstrating greater inhibition than the methanol extract. The largest inhibition zone measured 11.46 ± 0.00 mm against Klebsiella pneumoniae , whereas the smallest was 10.15 ± 0.01 mm against Staphylococcus aureus . Additionally, the synthesized CuO NPs exhibited significant antioxidant activity, achieving 77.3% at a concentration of 1000 µg/mL in the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) assay. This study successfully synthesized CuO NPs and evaluated their antibacterial and antioxidant properties and inspired the researcher to further research, development, and formulation. Summary The study successfully synthesized copper oxide nanoparticles (CuO NPs) using hydrated copper sulfate and leaf extract from Croton macrostachyus as reducing and capping agents, with characterization confirming nanoparticle formation through techniques like UV–Vis, XRD, and FT‐IR spectroscopy. The CuO NPs demonstrated significant antibacterial activity against both Gram‐positive and Gram‐negative bacteria, with the largest inhibition zone of 11.46 mm against Klebsiella pneumoniae and notable effectiveness compared to the methanol extract of the leaf. The synthesized CuO NPs exhibited strong antioxidant properties, achieving 77.3% inhibition in the DPPH assay at a concentration of 1000 µg/mL, highlighting their potential for further research and application in health‐related fields.