One step synthesis of functionalized carbon dots for the ultrasensitive detection of Escherichia coli and iron (III)

Highly photoluminescent carbon dots with a PL quantum yield of 26% have been prepared in one step by hydrothermal treatment of orange juice. Due to high photostability and low toxicity these carbon dots are demonstrated as excellent probes in cellular imaging.

The synthesis of water-soluble nitrogen-doped carbon dots has received great attention, due to their wide applications in oxygen reduction reaction, cell imaging, sensors, and drug delivery. Herein, nitrogen-doped, carbon-rich, highly photoluminescent carbon dots have been synthesized for the first time from ammonium citrate under hydrothermal conditions. The obtained nitrogen-doped carbon dots possess bright blue luminescence, short fluorescence lifetime, pH-sensitivity and excellent stability at a high salt concentration. They have potential to be used for pH sensors, cell imaging, solar cells, and photocatalysis.

A facile, economical and straightforward hydrothermal strategy is used to prepare highly luminescent nitrogen-doped carbon quantum dots (N-CQDs) by using folic acid as both carbon and nitrogen sources. The as-prepared N-CQDs have an average size of 4.5 ± 1.0 nm and exhibit excitation wavelength-dependent fluorescence with the maximum emission and excitation at 390 and 470 nm, respectively. Furthermore, due to the effective quenching effect of Hg(2+) ions, such N-CQDs are found to serve as an effective fluorescent sensing platform for lable-free sensitive detection of Hg(2+) ions with a detection limit of 0.23 μM. The selectivity experiments reveal that the fluorescent sensor is specific for Hg(2+) even with interference by high concentrations of other metal ions. Most importantly, the N-CQDs-based Hg(2+) ions sensor can be successfully applied to the determination of Hg(2+) in tap water and real lake water samples. With excellent sensitivity and selectivity, such stable and cheap carbon materials are potentially suitable for monitoring of Hg(2+) in environmental application.