Green Synthesis, Characterisation and Antimicrobial Evaluation of Copper Oxide Nanoparticles Using Carica papaya Leaf Extract

<title>Abstract</title> <p> The global Interest in sustainable and low-cost routes to metal nanoparticles has grown steadily, and green synthesis has become an attractive option, particularly for antimicrobial applications. Conventional chemical and physical routes often rely on hazardous reagents and consume large amounts of energy, which has encouraged the search for greener alternatives. In this work, copper oxide nanoparticles (CuO NPs) were synthesized using an aqueous leaf extract of <italic>Carica papaya</italic> and evaluated for antibacterial activity against two clinically relevant bacterial strains. The extract acted as both reducing and capping agent, and the products were characterised by ultraviolet–visible (UV–Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). UV–Vis spectra showed strong absorption in the ultraviolet region with a maximum near 314 nm, consistent with the formation of copper oxide rather than metallic copper. FTIR identified hydroxyl, carbonyl and amide groups, indicating that phenolic compounds and proteins from the extract were involved in reduction and surface stabilisation. XRD confirmed a crystalline product with an estimated crystallite size of 35–45 nm. Antibacterial activity was assessed by agar well diffusion and minimum inhibitory concentration (MIC) against <italic>Escherichia coli</italic> and <italic>Staphylococcus aureus</italic> . The nanoparticles produced concentration-dependent inhibition, with larger zones against <italic>S. aureus</italic> , and an MIC of 500 µg/mL for both organisms. These findings indicate that <italic>C. papaya</italic> -mediated CuO nanoparticles are stable, environmentally friendly antibacterial agents with potential value in pharmaceutical and biomedical applications. </p>