Biosynthesis of Metal Oxide Nanoparticles: Synthesis, Characterization, and Biological Applications: A Review

The plant-mediated biosynthesis of metal oxide nanoparticles (MONPs) has gained significant attention as a green, cost-effective, and sustainable alternative to conventional chemical and physical synthesis methods. By utilizing bioactive phytochemicals such as phenolics, flavonoids, alkaloids, terpenoids, and proteins, plant extracts act as natural reducing, capping, and stabilizing agents during nanoparticle formation. This eco-friendly approach avoids toxic reagents and harsh conditions, enabling controlled synthesis of nanoparticles with tunable size, shape, and surface properties. Various metal oxides, including zinc oxide (ZnO), titanium dioxide (TiO₂), copper oxide (CuO), nickel oxide (NiO), silver oxide (Ag₂O), and iron oxide (Fe₂O₃/Fe₃O₄), have been successfully synthesized using extracts derived from different plant parts such as leaves, roots, flowers, barks, and fruits. Characterization of these biosynthesized MONPs typically involves a range of instrumental characterization techniques. Synthesis parameters like pH, temperature, and extract concentration strongly influence the physicochemical attributes of the nanoparticles. This review presents a comprehensive overview of eco-friendly strategies for synthesizing MONPs, with a particular focus on their green synthesis from different plant parts through rapid and sustainable approaches. It discusses various synthesis methodologies, characterization techniques, and the resulting functional properties of the biosynthesized MONPs, supported by notable proof-of-concept studies. Furthermore, the review highlights the wide range of biomedical applications of plant-mediated MONPs, emphasizing their remarkable antimicrobial, antioxidant, anticancer, and anti-inflammatory activities. However, challenges remain in achieving reproducibility, large-scale synthesis, and mechanistic understanding. Considering the limited available data and the increasing industrial interest in plant-mediated MONPs, this review seeks to encourage researchers from diverse scientific fields to further investigate the potential of naturally synthesized MONPs and their emerging applications, thereby fostering progress in sustainable materials science and green nanotechnology.