Recent advances in near-infrared emitting lanthanide-doped nanoconstructs: Mechanism, design and application for bioimaging

Lanthanide-doped nanoconstructs (LDNCs) have been widely studied in the biomedical field. Especially, LDNCs with near-infrared (NIR) fluorescence show great promise in biological imaging. The fluorescence in the NIR window (700-1700 nm) affords increased tissue penetration due to the reduced light absorption, photon scattering and autofluorescence. Actually, LDNCs with various lanthanide-dopings can emit ultraviolet (UV), visible (VIS) and NIR photons through upconversion (UC) and downconversion (DC) processes. Moreover, there are review papers introducing different aspects of bioimaging based on LDNCs. Nevertheless, there has not been a review that systematically summarizes NIR fluorescent LDNCs. Herein, we summarize the recent progress made on NIR fluorescence imaging by highlighting the increasingly developing trend of NIR emitting LDNCs. The NIR emission mechanism of LDNCs activated by different lanthanide ions was discussed in detail, and their advantages as NIR fluorescent probes will be systematically introduced. From the aspect of realizing multimodal imaging, the advances made by combining magnetic resonance imaging (MRI), computed tomography (CT) and so on with NIR optical imaging were summarized. Finally, we discuss the superiority of NIR-II (1000-1700 nm) emitting LDNCs when applied in biomedical imaging, with an emphasis on how to use them to realize imaging guided cancer therapy. (C) 2018 Elsevier B.V. All rights reserved.