Multifunctional NaYF4:Nd/NaDyF4 nanocrystals as a multimodal platform for NIR-II fluorescence and magnetic resonance imaging

Abstract

Recently, multimodal imaging nanoprobes based on the complementary advantages of various imaging methods have attracted considerable attention due to their potential application in the biomedical field. As important bioimaging nanoprobes, lanthanide-doped nanocrystals (NCs) would be expected to improve the related biophotonic technology through integrated multimodal bioimaging. Herein, water-soluble and biocompatible NaYF₄:Nd/NaDyF₄ NCs were prepared by a solvothermal method combined with hydrophobic interaction with phospholipids as a capping agent. The NaYF₄:Nd/NaDyF₄ NCs exhibit excellent colloidal stability under physiological conditions. Compared with the bare NaYF₄:Nd³⁺ NCs, the second near-infrared (NIR-II, 1000–1700 nm) fluorescence intensities of Nd³⁺ ions in the NaYF₄:Nd/NaDyF₄ core–shell NCs at the emissions of 1058 nm and 1332 nm are enhanced by 3.46- and 1.75-fold, respectively. Moreover, the r₂ value of NaYF₄:Nd/NaDyF₄ NCs as T₂-weighted contrast agents is calculated to be 44.0 mM⁻¹ s⁻¹. As a novel multimodal imaging nanoprobe, the NaYF₄:Nd/NaDyF₄ NCs can be employed for both NIR-II fluorescence and magnetic resonance imaging (MRI). The phospholipid-modified NaYF₄:Nd/NaDyF₄ NCs demonstrate in vitro and in vivo multimodal NIR-II fluorescence imaging and MRI of HeLa cells and tumors, respectively. This study provides an effective strategy for the development of novel multimodal probes for the medical application of nanomaterials.