Green-Synthesized Copper and Copper Oxide Nanoparticles: Structural Characterization and Evaluation of Biological Activity

Copper-based nanoparticles, especially metallic copper (Cu NPs) and copper oxide (CuO NPs), have attracted increasing attention due to their redox activity, biological efficacy, and technological applications. However, conventional chemical synthesis often involves toxic reagents, limiting their biomedical applicability. In this context, plant-mediated green synthesis has evolved and has become a sustainable and cost-effective alternative. This review provides a comprehensive overview of recent advances in the biosynthesis of Cu and CuO nanoparticles using plant extracts. The main synthesis pathways are examined, with emphasis on the role of phytochemicals as reducing, stabilizing, and capping agents, as well as the influence of reaction parameters on nanoparticle yield. The review highlights the diversity of plant species and extract types used and clarifies their effects on nanoparticle size, morphology, oxidation state, and surface chemistry. Key physicochemical characterization techniques (ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), electron microscopy, and zeta potential analysis) are systematically discussed. Moreover, a summary of in vitro and in vivo biological activities is provided, including antimicrobial, antioxidant, cytotoxic, anticancer, wound-healing, and plant-growth-promoting effects. Overall, plant-mediated copper-based nanoparticles demonstrate significant potential as biofunctional nanomaterials. Nevertheless, challenges concerning reproducibility, mechanistic understanding, standardization and toxicological evaluation must be addressed to facilitate reliable translation into biomedical applications.