"On-off-on" detection of Fe3+ and F-, biological imaging, and its logic gate operation based on excitation-independent blue-fluorescent carbon dots.

A fluorescent nanoprobe based on carbon dots (CDs) has been facilely synthesized by a one-step hydrothermal pyrolysis of salicylic acid and utilized for the sequential detection of Fe3+ and F- in vitro. The fluorescence of CDs can be extinguished dramatically by Fe3+ based on static quenching and subsequently recovery upon addition of F- due to the formation of stabler FeF3. The probe exhibits high selectivity and sensitivity toward Fe3+ and F- with a good linearity in the range of 10-300 μM and 0.1-200 μM, respectively, and a low detection limit of 52 nM and 8.5 nM, respectively. More importantly, as-prepared CDs with exceedingly fluorescence stability, negligible toxicity and superior biocompatibility have been expanded for detection Fe3+ and F- in living cell and Escherichia coli. Furthermore, an "AND" logic gate based on as-obtained CDs has been constructed.