Nd³⁺-doped LiYF₄ nanocrystals for bio-imaging in the second near-infrared window

The fluorescent probes working in the near-infrared (NIR) window have unparalleled advantages of a high penetration depth and low interference from autofluorescence. In this paper we introduced a rare-earth doped nanoprobe working in this region with a narrow emission band, a high efficiency, and good bio-compatibility. The newly-developed host material LiYF₄ managed to strengthen the emission intensity and generate a fine structure of the emission peaks. After the optimization of the doping ratio of Nd³⁺ and surface modification, the LiYF₄:5%Nd³⁺ probe could reach a penetration depth of 3-5 mm and could be successfully utilized in lymphatic imaging, with a signal-to-noise ratio of 14.8 in vivo and a resolution of ∼0.2 mm in circulatory imaging. This probe may be further used in bio-detection and the host material itself may replace the traditional NaYF₄ in some aspects of applications.