Radiolabelled ZnO, Iron Oxide-Based, and Gold Nanoparticles for Cancer Therapy: Synthesis, Surface Engineering, and Radiolabelling Strategies.

Radiolabelled nanoparticles are increasingly investigated as multifunctional platforms for cancer imaging, biodistribution tracking, dosimetry, and radionuclide-based therapy. This review focuses on three representative inorganic nanoplatforms: zinc oxide (ZnO), iron oxide-based, and gold (Au) nanoparticles. These systems were selected because they combine distinct physicochemical properties with versatile surface engineering and radiolabelling strategies. ZnO nanoparticles offer pH-responsive behaviour and drug-delivery potential; iron oxide-based nanoparticles provide magnetic functionality, Magnetic resonance imaging (MRI) compatibility, and opportunities for magnetic hyperthermia or local nanobrachytherapy; and Au nanoparticles enable stable surface functionalization, radiometal chelation, radiosensitisation, photothermal effects, and alpha or beta-emitter-based local therapy. The review critically discusses synthesis and surface-modification methods, chelator-mediated and chelator-free radiolabelling, coating-assisted and anchoring-mediated strategies, and the influence of these factors on radiochemical stability, biodistribution, tumour uptake, therapeutic response, toxicity, and clearance. A function-based comparison of the reviewed studies highlights that many systems demonstrate efficient radiolabelling and imaging capability, whereas fewer provide direct in vivo therapeutic efficacy, long-term toxicity, or metabolic clearance data. Overall, radiolabelled ZnO, iron oxide-based, and Au nanoparticles show strong potential for cancer theranostics, tumour-to-organ distribution, therapeutic benefit, and safety.