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 μM and 0.000549 μM, respectively, in a linear range of 0.5 μM‐100 μM and 0.5 μM‐5 μM 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 μg/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.

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Arsenic, a common pollutant, harms human health, and its WHO's permissible is 10 μg/L in drinking water. This research aimed to develop a paper‐based point of care test (POCT) device for rapid detection of arsenic with a concentration of ~10 μg/L in potable water. In this, arsenic was converted to arsine gas, which was identified by a paper sensor by producing a characteristic color due to specificity of the reaction. The sensor was constructed by impregnating gold chloride (NaAuCl4) on a paper strip. The device had a very good response time, nearly 4 and 2 min for arsenic concentrations of (10–20) and above 20 (20–500) μg/L, respectively. The device also gave decent results for the field samples like river and groundwater. The device could be used for both qualitative and quantitative assays. ImageJ software was used for quantitative estimation, which accorded with atomic absorption spectroscopy (AAS) results.