Fluorescence imaging in the second near-infrared region(NIR-Ⅱ,1000–1700 nm)is more desirable than visible(450– 700 nm)and traditional NIR-I imaging(700–950 nm)owing to greatly reduced photon absorption and scattering by tissues,as well as negligible tissue autofluorescence,which promises high-fidelity imaging of deeper tissues and organs.