Bismuth-Loaded Poly(α-amino acid) Nanoparticles for CT and Fluorescence Bimodal Imaging

X-ray computed tomography (CT) offers high spatial resolution and deep tissue penetration, but its low sensitivity limits early disease diagnosis. In contrast, fluorescence imaging (FI) provides high sensitivity, suffering from poor spatial resolution and limited tissue penetration. Combining CT and FI creates a complementary imaging method. Herein, we report bismuth-loaded poly(α-amino acid) nanoparticles (abbreviated as Bi NPs including Bi@POS, Bi@POS-FITC, and Bi@POS-ICG) for CT and fluorescence bimodal imaging. Bi NPs exhibit superior X-ray attenuation and fluorescence emission properties by integrating bismuth complexes with fluorescent dyes, including fluorescein isothiocyanate (FITC) and indocyanine green (ICG). The catechol moieties in poly(α-amino acid)s not only chelate Bi³⁺ but also exhibit reactive oxygen and nitrogen species (RONS) scavenging activity. In vitro and in vivo experiments demonstrate that Bi NPs have superior bimodal imaging performance, significantly enhanced CT contrast, and prolonged fluorescence signals, suggesting their great potential as bimodal contrast agents for diagnosis applications.