In this study, we have reported the synthesis of luminescent carbon dots (CDs) from indigenous potato sources by simple heating reactions. The as-synthesized CDs exhibited an average size of ~ 5.97 nm with a quantum yield (QY) of 6.08%. Furthermore, the CDs possessed high water-solubility, possibly due to the presence of COOH and OH groups on their surfaces. The quenching of luminescence of the CDs specifically by Cr6+ and Fe3+ ions was used to detect chromium and iron in the water sample. The minimum limit of detection (LOD) for Cr6+ and Fe3+ ions was found to be 0.012 mu M and 0.000549 mu M, respectively, in a linear range of 0.5 mu M-100 mu M and 0.5 mu M-5 mu M for Cr6+ and Fe3+, respectively, which was well below the concentration specified by WHO. We used our sensing system to detect the metal ions in water from the Brahmaputra River as well as in tannery water. In addition, the MTT-based cell viability experiments showed that the CDs were nontoxic within 200 mu g/mL. High quantum yield and the easy uptake of CDs enabled the quick labelling of cytoplasm of the HeLa cells, which can be further attributed to bioimaging applications.