A facile aqueous chemical approach is developed for one-pot synthesis of the nanocomposites of heavily doped semiconductor nanoparticles (Cu2-xSe NPs) and reduced graphene oxide (rGO) at room temperature, wherein the reduction of GO and the in situ growth of Cu2-xSe NPs on rGO sheets occur simultaneously. The as-prepared Cu2-xSe/rGO nanocomposites exhibit a well-defined near-infrared (NIR) localized surface plasmon resonance (LSPR), which arises from free carriers (holes) and could be tuned from 1360 to 1050 nm by varying the reaction time, owing to the increase of the free carrier density in the valence band of Cu2-xSe NPs. This approach not only offers an efficient strategy to synthesize the self-doped Cu2-xSe/rGO nanocomposites with strong and tunable NIR absorption, but also develops new light scattering nanoprobes with good biocompatibility as well as unique optical properties for in vitro cellular dark-field microscopic imaging (iDFM).