Neodymium-doped NaHoF4 nanoparticles as near-infrared luminescent/T2-weighted MR dual-modal imaging agents in vivo

Abstract

The achievement of efficient near-infrared (NIR) luminescence of lanthanide ions in a paramagnetic nanoparticle (NP) host is highly desirable to optimize the performance of multimodal bioprobes. Herein, we present a facile coprecipitation method to prepare highly uniform NaHoF₄:Nd³⁺ nanoplates. Upon NIR excitation at 785 nm, efficient NIR luminescence of Nd³⁺ can be obtained from the paramagnetic NaHoF₄ hosts. More interestingly, due to energy transfer from the excited state of Nd³⁺ to the adjacent Ho³⁺, NIR emission at around 1200 nm from Ho³⁺ ions is also observed. The r₂ value of NaHoF₄:Nd³⁺ NPs reaches 143.7 s⁻¹ mM⁻¹ at a high magnetic field of 11.7 T. By modifying with hydrophilic alpha-cyclodextrin, the NaHoF₄:Nd³⁺ NPs were further successfully applied for the NIR luminescent/T₂-weighted MR dual-modal in vivo imaging of nude mice, high contrast NIR imaging of the liver and T₂-weighted MR imaging of stem cells in the mouse brain using the NaHoF₄:Nd³⁺ NPs as multimodal bioprobes.