Facile and cost-effective preparation of carbon quantum dots for Fe3+ ion and ascorbic acid detection in living cells based on the on-off-on fluorescence principle

A facile and cost-effective route of fabricating carbon quantum dots (CQDs) was proposed via simply hydrothermal treatment of lignin. Because of abundant aromatic structure and functional groups derived from lignin, the prepared CQDs (LCQDs) showed unique chemical and optical property. A remarkable fluorescence quenching effect of Fe3+ on LCQDs was found, resulting from the formation of non-fluorescence complex between LCQDs and Fe3+. This on-off fluorescence CQDs nanoprobe for Fe3+ allowed a wide linear range of 50-650 mu M with the limit of detection (LOD) as low as 196 nM. Besides, ascorbic acid (AA) was found to reduce Fe3+ to Fe2+, leading to the recovery of the LCQDs fluorescence and a good linearity in range of 0-350 mu M with a LOD of 5.34 mu M. Furthermore, this sensing platform was successfully used for Fe3+ and AA monitoring in biological samples and intracellular imaging without surface modification.