Sub-10 nm BaLaF5:Mn/Yb/Er nanoprobes for dual-modal synergistic in vivo upconversion luminescence and X-ray bioimaging

Abstract

Small-sized BaLaF₅:Mn/Yb/Er upconversion nanoparticles (UCNPs) were successfully synthesized for dual-modal X-ray and upconversion (UC) luminescence bioimaging by a simple solvothermal method. The size, shape, and UC luminescence intensity of the as-prepared UCNPs can be readily modified by changing the contents of Mn²⁺. The size of BaLaF₅ UCNPs doped with Mn²⁺ decreased largely compared with Mn-free UCNPs. When increasing the content of Mn²⁺ from 5% to 20%, the size of UCNPs was gradually increased from 6.5 nm to 9.7 nm. The as-prepared BaLaF₅ UCNPs doped with 20% Mn²⁺ present intense UC luminescence. The in vitro UC luminescence imaging of HeLa cells and localized spectra detected from HeLa cells and the background based on these BaLaF₅:Mn/Yb/Er (20/20/2%) UCNPs indicate that this sample can serve as an ideal bioprobe with the absence of autofluorescence under the excitation of 980 nm laser. Moreover, an obvious UC signal was observed in in vivo UC bioimaging, demonstrating that these BaLaF₅:Mn/Yb/Er (20/20/2%) UCNPs can also be used as bioprobes for whole body optical bioimaging. In addition, owing to the high X-ray mass absorption coefficients of Ba²⁺, La³⁺ and the doped Yb³⁺, the simultaneous X-ray and UC in vivo bioimaging of a nude mouse further demonstrate that the as-prepared UCNPs can be successfully used as dual-modal bioprobes. Ex vivo UC bioimaging revealed that these UCNPs gathered at the lung of a mouse at the initial time, demonstrating that this sample was suitable for the detection of the lung diseases. In addition, the cytotoxicity test showed that the UCNPs possessed little toxicity. Therefore, the small-sized BaLaF₅:Yb/Er/Mn UCNPs are ideal nanoprobes for dual-modal UC luminescence/X-ray bioimaging with non-autofluorescence, and enhanced detection of the lung diseases.