Seed-mediated synthesis and biosynthesis of iron oxide nanoparticles.

Metal-based nanoparticles, particularly iron oxide nanoparticles (IONPs), have attracted considerable attention due to their versatile applications in magnetic resonance imaging (MRI), magnetic hyperthermia, stem cell tracking, cancer therapy, and targeted drug delivery. However, achieving uniform, highly crystalline IONPs remains a significant challenge, as conventional synthesis methods are highly sensitive to variables, such as temperature, pH, and the types of stabilizing and reducing agents used. This review explores two prominent synthesis strategies-seed-mediated synthesis and biological (green) syntheses that have been widely adopted to overcome listed challenges and enable the controlled fabrication of isotropic and anisotropic IONPs with uniform size and morphology. Seed-mediated synthesis, which can be classified into homogeneous and heterogeneous approaches, offers precise control over nanoparticle growth and shape. When combined with established synthesis techniques, such as co-precipitation, thermal decomposition, and solvothermal methods, seed-mediated strategies can yield IONPs with low polydispersity and high crystallinity. However, these approaches often rely on expensive and environmentally unfriendly materials, including polymers, surfactants, and organic solvents. In contrast, biosynthesis harnesses the natural reducing, capping, and stabilizing agents found in biological systems-such as plant extracts, bacteria, fungi, or algae-to produce IONPs under mild, eco-friendly conditions. Aligned with the principles of green chemistry, biosynthetic methods offer a sustainable and cost-effective alternative for nanoparticle production, with reduced toxicity and improved biocompatibility. This review presents a comprehensive comparison of seed-mediated and biosynthesis methods for IONPs, emphasizing their respective advantages, limitations, and future potential in advancing nanomaterials' fabrication for biomedical applications. Additionally, for clinical use, adherence to Good Manufacturing Practices (GMP) is essential to ensure the consistent quality and safety of IONP-based products. Post-market surveillance also plays a critical role in evaluating long-term therapeutic efficacy and safety, thereby enhancing patient outcomes and trust in nanoparticle-based technologies. Compliance with GMP is essential to maintain consistent quality and safety standards for IONP-based medical products. Furthermore, ongoing post-market surveillance is crucial for monitoring long-term efficacy and potential adverse effects, thereby supporting patient safety and therapeutic reliability.