Biocompatible and low-cost iodine-doped carbon dots as a bifunctional fluorescent and radiocontrast agent for X-ray CT imaging†

Carbon dot-based radiocontrast agents have recently sparked the interest of researchers owing to their better contrasting capabilities, simple synthesis protocols, high colloidal stability, and good biocompatibility. In this study, we propose for the first time the synthesis of iodine-doped carbon dots (I-CDs) using low-cost reagents such as citric acid (C₆H₈O₇), urea (CH₄N₂O) and potassium iodide (KI). The as-prepared I-CDs demonstrated excellent colloidal stability (with a zeta potential value of −64.7 mV), excitation-dependent fluorescent properties (with a maximum quantum yield of ∼8.9%), and a mean iodine concentration of ∼4.67 wt%. Notably, the as-prepared I-CDs displayed greater X-ray attenuation efficiency (42.87 HU mL mg⁻¹) as compared to the commercially employed iopromide radiocontrast agent (30.98 HU mL mg⁻¹). Furthermore, ATPase activity, cytotoxicity analysis with HeLa, NHDF, HEK293, and A549 cell lines, and live-cell imaging experiments of the Drosophila neuroblasts in intact brain lobes suggested high biocompatibility and nontoxicity of the prepared I-CDs. Overall, biocompatible and low-cost I-CDs show great promise as bifunctional radiocontrast and fluorescent agents for biomedical applications.