Cellulose-based yellow-green emitting carbon dots with large Stokes shift as effective "turn off-on" fluorescence...

Hexavalent chromium (Cr (VI)) is highly carcinogenic to humans. Ascorbic acid (AA) deficiency can be hazardous to health. And the dual-effect fluorescence detection of them is an important research topic. Carbon dots (CDs) based on cellulose are excellent candidates for the fluorescence probes due to their low cost and environmental friendliness. But most of them exhibit shortwave emission, small Stokes shift and poor fluorescence performance, all of which limit their use. Therefore, there is an urgent need for cellulose CDs with longer emission wavelengths and larger Stokes shifts in dual-effect fluorescence detection of Cr (VI) and AA.

Under optimal conditions (180 °C, 12 h), we prepared cellulose-based nitrogen-doped carbon dots (N-CDs) by a simple one-step hydrothermal process, which display longer emission wavelengths (ex: 370 nm, em: 510 nm), larger Stokes shifts (140 nm) and high fluorescence quantum yield (QY: 19.27 %). The continuous "turn-off" and "turn-off-on" fluorescence detection platforms were constructed based on the internal filtering effect (IFE) between Cr⁶⁺ and N-CDs, and Cr⁶⁺ reduced to Cr³⁺ by AA at pH = 6. The platform has been successfully simultaneous detect Cr (VI) and AA with a wide range of 0.01-40 μM and 0.1-100 μM. And the lowest limits of detection (LOD) are 0.0303 μM and 0.072 μM, respectively. In the presence of some other metals, non-metal ions and water-soluble acids in the fruits, this fluorescent platform can demonstrate a high level of interference immunity.

This represents the first yellow-green cellulose-based N-CDs with large Stokes shift for dual-effect detection of Cr (VI) and AA in real water samples and fresh fruits. The fluorescence detection platform has the advantage of low volume detection. Less than 2 mL of sample is required for testing and results are available in <5 min. This method is rare and supply a novel idea for the quantitative monitoring of Cr (VI) and AA.