From 0D to 2D: Synthesis and bio-application of anisotropic magnetic iron oxide nanomaterials

Magnetic iron oxide nanoparticles (MIPs) have garnered significant scientific interest due to their magnetic properties and unique features, including low toxicity, colloidal stability, and surface engineering capability. Recent advances in nanoparticle synthesis have enabled the development of MIPs with precise control over their physicochemical properties, making them suitable for medical applications. Anisotropic MIPs have demonstrated shape-dependent performance in various bio-applications, leading to increased research moving from traditional zero-dimensional (0D) morphology towards one-dimensional (1D) and two-dimensional (2D) topology. While these anisotropic materials offer enhanced properties for specific applications, a critical and systematic comparison of their anisotropy effects is lacking in the literature. This review seeks to fill this current gap in the literature and provides a comprehensive summary of the last two decades of research on magnetic iron oxide materials with different shapes in biomedical applications. The paper will discuss the theoretical mechanisms of shape-dependent effects, primary synthetic approaches of 0D, 1D, and 2D MIP materials, biomedical applications, and biological behaviors. In addition, the review identifies critical challenges and open questions that need to be addressed. The proposed research directions outlined in this review have the potential to revitalize the use of “old” MIPs towards future physicochemical and biomedical applications.