Developing effective methods for the instant detection of Cu and S is highly desired in the biological and environmental fields. Herein, a novel fluorescent nanoprobe was elaborately designed and synthesized by grafting a phenanthroline derivative onto the surface of carbon dots (CDs). The obtained functionalized CDs (FCDs) exhibited blue fluorescence (FL) with excellent photostability and possessed a mean diameter around 4 nm. Cu can be selectively captured by the phenanthroline group of FCDs to generate an absorptive complex in situ, leading to obvious quenching of the FCDs' FL signal through an inner filter effect. Furthermore, the FL of the FCD⁻Cu can be effectively recovered by S anions due to the release of FCDs from the FCD⁻Cu complex owing to the formation of stable CuS ( = 1.27 × 10) between S and Cu. The detection limits of the FCDs were determined to be 40.1 nM and 88.9 nM for Cu and S, respectively. Moreover, this nanoprobe can also be used for the imaging of intracellular Cu and S, which shows strong application prospects in the field of biology.