Multifunctional BaYbF₅: Gd/Er upconversion nanoparticles for in vivo tri-modal upconversion optical, X-ray computed tomography and magnetic resonance imaging

Development of high-quality upconversion nanoparticles (UCNPs) with combination of the merits of multiple molecular imaging techniques, such as, upconversion luminescence (UCL) imaging, X-ray computed tomography (CT), and magnetic resonance (MR) imaging, could significantly improve the accuracy of biological diagnosis. In this work, multifunctional BaYbF₅: Gd/Er (50:2 mol%) UCNPs were synthesized via a solvothermal method using oleic acid (OA) as surface ligands (denoted as OA-UCNPs). The OA-UCNPs were further treated by diluted HCl to form ligand-free UCNPs (LF-UCNPs) for later bioimaging applications. The cytotoxicity assay in HeLa cells shows low cell toxicity of these LF-UCNPs. Owing to the efficient UCL of BaYbF₅: Gd/Er, the LF-UCNPs were successfully used as luminescent bioprobe in UCL bioimaging. And, X-ray CT imaging reveals that BaYbF₅: Gd/Er UCNPs can act as potential contrast agents for detection of the liver and spleen in the live mice owing to the high-Z elements (e.g., Ba, Yb, and Gd) in host matrix. Moreover, with the addition of Gd, the as-designed UCNPs exhibit additional positive contrast enhancement in T₁-weighted MR imaging. These findings demonstrate that BaYbF₅: Gd/Er UCNPs are potential candidates for tri-modal imaging. - Graphical abstract: Multifunctional BaYbF₅: Gd/Er upconversion nanoparticles with efficient upconversion emission, high absorption coefficient, predominant paramagnetic behavior, and low biological toxicity were demonstrated for tri-modality in vivo UCL, CT and MR imaging. Display Omitted - Highlights: • The multifunctional UCNPs with high monodispersity were synthesized. • The UCNPs present large r₁ value and binary CT contrast agents. • These UCNPs were demonstrated as optimal probes for tri-modal bioimaging.