Facile synthesis of polyethylenimine coated Bi₂O₃/Gd₂O₃ composite nanoparticles as multimodal MRI/CT contrast agents

Bimodal imaging contrast agents integrated magnetic resonance imaging (MRI) and computed tomography (CT) have attracted significant attention in recent years. In this study, we report the design and synthesis of Bi₂O₃/Gd₂O₃@polyethylenimine composite nanoparticles (BGO@PEI NPs) by a facile wet chemistry method. The BGO@PEI NPs exhibit uniform spherical morphology with an average core diameter of around 5.8 nm, high colloidal stability, and excellent biocompatibility. Comprehensive characterization confirmed their efficient r ₁ relaxation enhancement and strong X-ray attenuation. The BGO@PEI NPs revealed a superior MRI T ₁ contrast performance with a longitudinal relaxivity (r ₁) of 16.52 mM^-1 s^-1, exceeding that of clinical MRI agents, while also exhibited a CT attenuation coefficient of 16.59 HU mM^-1 at 80 kV. In vivo imaging confirmed significant tumor accumulation and dual MRI/CT signal enhancement, with CT intensity increasing from 21.5 to 80.4 HU and T ₁-weighted ΔSNR rising by 75% within 60 min post-injection. These results demonstrate that BGO@PEI NPs represent a promising multifunctional platform for dual-modal MRI/CT imaging and potential applications in precision diagnostics.