Engineering Core–Shell Structured Rare-Earth Nanomaterials for Deep Tissue Tumor Visualization

This study develops europium-based core–shell rare-earth nanoparticles for in vivo fluorescence imaging of tumors. The nanoparticles were synthesized via co-precipitation and coated with silica and polyethylene glycol (PEG) to enhance stability and colloidal dispersion. Scanning electron microscopy (SEM) revealed a uniform spherical morphology with an average diameter of 30 ± 5 nm. Fluorescence spectroscopy demonstrated strong emission in the 615–655 nm range upon excitation at 785 nm, indicating suitable optical properties for in vivo imaging applications. In vivo fluorescence imaging in tumor-bearing mouse models showed selective accumulation of the nanoparticles in tumor tissue, with fluorescence intensity peaking at 12 hours post-injection. Quantitative analysis revealed a tumor-to-background fluorescence ratio (TBR) of 11.0 ± 1.5 at the peak time point. Biodistribution analysis indicated predominant accumulation in the liver (35 ± 4%) and spleen (18 ± 3%), along with moderate renal clearance (22 ± 3%), while minimal accumulation was observed in the lungs and heart. No obvious acute toxicity was observed within the short observation period, as assessed by liver and kidney function markers and histopathological examination. These results suggest that the europium-based core–shell nanoparticles exhibit effective tumor targeting and favorable short-term in vivo behavior, supporting their potential utility as fluorescent probes for tumor imaging in animal models.