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

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 r(2) 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/T-2-weighted MR dual-modal in vivo imaging of nude mice, high contrast NIR imaging of the liver and T-2-weighted MR imaging of stem cells in the mouse brain using the NaHoF4: Nd3+ NPs as multimodal bioprobes.