Highly sensitive and selective detection of 4-nitrophenol, and on-off-on fluorescence sensor for Cr (VI) and ascorbic acid detection by glucosamine derived n-doped carbon dots

[Display omitted] •This is the first report on the synthesis of N-CDs by glucosamine with ethylenediamine.•N-CDs showed good selectivity and sensitivity against 4-NP (LOD: 0.05 μM).•Served as an ‘on-off-on’ sensor for the successive sensing of Cr (VI) and Cr (VI)/AA.•Exhibited an acceptable recovery (%) and RSD (%) at real sample analysis. Here in, the fluorescent nitrogen doped carbon dots (N-CDs) were synthesized by microwave digestion method using glucosamine and ethylenediamine as raw materials for carbon and amine sources. Correspondingly, N-CDs formation was further confirmed through XPS, XRD, TEM and FT-IR techniques. And the optical properties were further investigated using fluorescence and UV–vis spectrophotometry. The synthesized N-CDs were used to explore its sensing ability against 4-nitrophenol (4-NP), Cr(VI), and Ascorbic acid. The sensing strategies of 4-NP, Cr(VI) and Cr(VI)/ascorbic acid had showed the promising detection limits such as 0.05, 0.08 and 0.15 μM respectively. The investigation related to the fluorescence emission quenching of N-CDs against 4-NP and Cr(VI) were attributed to the inner filter effect (IFE), however in case of AA sensing strategy, it was due to the weakening on IFE, results in restoring of fluorescence emission from 0.25 to 175 μM concentration range of AA against N-CDs/Cr(VI) fluorescent probe. Whereas to assess the practicality of the detection strategy, real sample analysis was also performed, which showed the acceptable rates of recoveries and relative standard deviations towards N-CDs/Cr (VI) and N-CDs/Cr(VI)/AA probes. All in all, the reported N-CDs can be utilized in environmental and biological applications.