Water-stable NaLuF4-based upconversion nanophosphors with long-term validity for multimodal lymphatic imaging

Multimodal imaging is rapidly becoming an important tool for biomedical applications because it can compensate for the deficiencies of individual imaging modalities. Herein, multifunctional NaLuF4-based upconversion nanoparticles (Lu-UCNPs) were synthesized though a facile one-step microemulsion method under ambient condition. The doping of lanthanide ions (Gd3+, Yb3+ and Er3+/Tm3+) endows the Lu-UCNPs with high T1-enhancement, bright upconversion luminescence (UCL) emissions, and excellent X-ray absorption coefficient. Moreover, the as-prepared Lu-UCNPs are stable in water for more than six months, due to the protection of sodium glutamate and diethylene triamine pentacetate acid (DTPA) coordinating ligands on the surface. Lu-UCNPs have been successfully applied to the trimodal CT/MR/UCL lymphatic imaging on the modal of small animals. It is worth noting that Lu-UCNPs could be used for imaging even after preserving for over six months. In vitro transmission electron microscope (TEM), methyl thiazolyl tetrazolium (MTT) assay and histological analysis demonstrated that Lu-UCNPs exhibited low toxicity on living systems. Therefore, Lu-UCNPs could be multimodal agents for CT/MR/UCL imaging, and the concept can be served as a platform technology for the next-generation of probes for multimodal imaging.