Ultrasmall Bi/Bi₂O₃ nanoparticles as biocompatible and efficient CT imaging contrast agents

Computed tomography (CT) imaging is a widely used diagnostic tool, but conventional iodine-based contrast agents suffer from limitations such as short circulation time and potential nephrotoxicity. In this study, we present a simple one-pot thermal decomposition method for synthesizing ultrasmall Bi/Bi₂O₃ nanoparticles (NPs) using a commercial Bi(NO₃)₃ precursor and a surfactant mixture of oleic acid and oleylamine. Oleylamine acts as a reducing agent, facilitating the conversion of Bi³⁺ to metallic Bi, while the Bi₂O₃ oxide layer is controlled by adjusting the oleic acid-to-oleylamine ratio. To enhance biocompatibility and aqueous dispersibility, the NPs are further modified with polyacrylic acid (PAA), resulting in Bi/Bi₂O₃@PAA NPs with an ultra-small size, high Bi content, and stability. X-ray attenuation measurements reveal that Bi/Bi₂O₃@PAA NPs exhibit superior contrast enhancement compared to the traditional iodine-based contrast agents, with increasing efficacy at higher tube voltages. Given their facile synthesis, excellent biocompatibility, and outstanding imaging performance, Bi/Bi₂O₃@PAA NPs hold significant promise as next-generation CT contrast agents for clinical applications.