Intense near-infrared-II luminescence from NaCeF4:Er/Yb nanoprobes for in vitro bioassay and in vivo bioimaging

Near-infrared (NIR) II luminescence between 1000 and 1700 nm has attracted reviving interest for biosensing due to its unique advantages such as deep-tissue penetration and high spatial resolution. Traditional NIR-II probes such as organic fluorophores usually suffer from poor photostability and potential long-term toxicity. Herein, we report the controlled synthesis of monodisperse NaCeF4:Er/Yb nanocrystals (NCs) that exhibit intense NIR-II emission upon excitation at 980 nm. Ce3+ in the host lattice was found to enhance the luminescence of Er3+ at 1530 nm with a maximum NIR-II quantum yield of 32.8%, which is the highest among Er3+-activated nanoprobes. Particularly, by utilizing the intense NIR-II emission of NaCeF4:Er/Yb NCs, we demonstrated their application as sensitive homogeneous bioprobes to detect uric acid with the limit of detection down to 25.6 nM. Furthermore, the probe was detectable in tissues at depths of up to 10 mm, which enabled in vivo imaging of mouse organs and hindlimbs with high resolution, thus revealing the great potential of these NaCeF4:Er/Yb nanoprobes in deep-tissue diagnosis.