An Extended NIR‐II Superior Imaging Window from 1500 to 1900 nm for High‐Resolution In Vivo Multiplexed Imaging Based on Lanthanide Nanocrystals

High‐resolution in vivo optical multiplexing in second near‐infrared window (NIR‐II, 1000–1700 nm) is vital to biomedical research. Presently, limited by bio‐tissue scattering, only luminescent probes located at NIR‐IIb (1500–1700 nm) window can provide high‐resolution in vivo multiplexed imaging. However, the number of available luminescent probes in this narrow NIR‐IIb region is limited, which hampers the available multiplexed channels of in vivo imaging. To overcome the above challenges, through theoretical simulation we expanded the conventional NIR‐IIb window to NIR‐II long‐wavelength (NIR‐II‐L, 1500–1900 nm) window on the basis of photon‐scattering and water‐absorption. We developed a series of novel lanthanide luminescent nanoprobes with emission wavelengths from 1852 nm to 2842 nm. NIR‐II‐L nanoprobes enabled high‐resolution in vivo dynamic multiplexed imaging on blood vessels and intestines, and provided multi‐channels imaging on lymph tubes, tumors and intestines. The proposed NIR‐II‐L probes without mutual interference are powerful tools for high‐contrast in vivo multiplexed detection, which holds promise for revealing physiological process in living body. We developed a series of novel lanthanide‐doped nanoparticles in the whole near‐infrared region (NIR) beyond 1700 nm. Inspired by the scattering and water absorption, we then defined the NIR‐II long‐wavelength (NIR‐II‐L, 1500 nm–1900 nm) window for high‐resolution multiplexed imaging of lymph, blood vessels and intestines.