Advances in holmium-doped nanostructures for cancer theranostics.

Nanoparticles (NPs) based on holmium or holmium-doped have attracted increasing attention in biomedicine, addressing the needs in cancer diagnostics and therapy due to their unique magnetic and optical properties. However, there are only a few comprehensive reviews addressing fabrication approaches and multifunctional applications. This paper focuses on holmium-based nanostructures, with a particular emphasis on Ho-doped superparamagnetic iron oxide nanoparticles (Ho-doped SPIONs), and their potential for targeted therapies. Both, holmium-doped and holmium-based nanoparticles offer their potential to enhance drug delivery through controllable size, surface modifications, and controlled release mechanisms, as well as use of them as β- emitters, an alternative to the conventional radiotherapy. However, optimization of the experimental conditions during synthesis is also crucial to safety in clinical use. This work reviews (1) the design of Ho-based NPs including Ho-doped SPIONs for theranostic applications, including (2) magnetic hyperthermia, (3) drug delivery, and (4) radiolabeling. It also highlights the current lack of data for Ho-doped SPIONs in (5) the near-infrared range and (6) magnetic resonance imaging, while discussing other Ho-based nanostructures reported in the literature. Additionally, this review paper shows limitations and future perspectives for clinical translation.