Long-Term Biodistribution of Fe3O4@Au Core–Satellite Nanoparticles Assessed by CT and MRI In Vivo

Nanoparticles combining gold and iron oxide are promising for a wide range of biomedical applications, including photothermal therapy, radiotherapy enhancement, drug delivery, and diagnostic imaging. However, their long-term biodistribution and safety profile remain largely unexplored. Here, we synthesized Fe3O4@AuNP core–satellite nanoparticles (Fe3O4@AuNPs) using femtosecond laser ablation, functionalized them with 15 kDa polyethylene glycol (PEG), and characterized them using a panel of physicochemical techniques. Healthy C57BL/6 mice received an intravenous injection of Fe3O4@AuNPs at 730 mg Au/kg and 82 mg Fe/kg, respectively. Biodistribution was monitored by computed tomography (CT) and magnetic resonance imaging (MRI) over 12 months, after which gold and iron concentrations were measured ex vivo, and long-term toxicity was assessed via histology and blood biochemistry. Nanoparticles accumulated predominantly in the liver and spleen. Quantitative analysis of CT images revealed a gradual decrease in gold content, while MRI showed a progressive reduction in negative contrast in the liver between 6 and 12 months, suggesting possible changes in the Fe3O4 core structure. Over the one-year observation period, no differences in behavior or body weight gain were detected between the treated and control groups. Histological examination revealed no pathological changes other than mild age-related alterations. These findings provide a baseline for the long-term behavior of laser-ablated core–satellite Fe3O4@AuNPs, which is essential for their further development in diagnostic and theranostic applications.