808 nm laser-triggered NIR-II emissive rare-earth nanoprobes for small tumor detection and blood vessel imaging.

Optical bioimaging in second near-infrared window (NIR-II, 1000-1700 nm) has been emerged as an indispensable tool for highly sensitive disease detection. In this work, intense NIR-II emissive polyacrylic acid (PAA) modified NaLuF4: Gd/Nd nanorods (PAA-NRs) with pure hexagonal phase and uniform size were explored for high sensitivity in vivo NIR-II bioimaging and optical imaging-guided small tumor detection. The NIR-II emission of the NaLuF4: Gd host can be readily adjusted by doping Nd3+, making it promising emission centered at 1056 nm and 1328 nm with high photo-stability. The time-dependent in vivo tracking results validate that the PAA-NRs are mainly accumulated in the reticuloendothelial system (RES) and excreted through the hepatic pathway. In addition, NIR-II optical imaging-guided small tumor (down to 5 mm) diagnosis was successfully achieved. Remarkably, in vivo small blood vessel with high spatial resolution (~105 μm) was detected clearly. And the histological tests reveal that our designed hydrophilic NRs present negligible toxicity effects and good biocompatibility in living animals. Besides the NIR-II emission, the PAA-NRs also present X-ray absorption features for X-ray bioimaging. These findings demonstrate that the explored lanthanide-based NRs with controllable size, efficient NIR-II emission and decent biocompatibility are promising NIR-II contrast agents for future biomedical applications, such as, early diagnosis of small tumor, vascular related disease imaging and angiogenesis diagnosis.