Bright red-emitting P, Br co-doped carbon dots as “OFF-ON” fluorescent probe for Cu2+ and L-cysteine detection

Carbon dots (CDs) with long-wavelength-emission and high quantum yield (QY) are the focus of current research, compared with widely-investigated blue-emitting CDs. Herein, bright red-emitting CDs were synthesized by hydrothermal reaction at 200 °C for 3 h. CDs prepared by p-Phenylenediamine (pPD) exhibits a weak red band at 635 nm under an excitation wavelength of 450 nm. Adding (NH 4 ) 2 HPO 4 and KBr as P and Br precursors, the red emission peak at 610 nm, which shows a peak blue-shift about 25 nm with a dramatic emission enhancement up to 20-folds by co-doping of P, Br atoms into CDs. The corresponding QY value of P, Br-doped CDs (P, Br-CDs) was greatly improved to 11.3% as compared to bare CDs’ (0.55%). Furthermore, P, Br-CDs show a remarkable luminescent turn-off response after adding copper ions (Cu 2+ ). In addition, the quenched luminescence of P, Br-CDs/Cu 2+ complex could be recovered by the chelation between Cu 2+ and L -cysteine ( L -Cys) after adding L -Cys. This fluorescence “ON-OFF-ON” protocol could be applied for sequent Cu 2+ and L -Cys detection, and offer a linear range of 0–150 μM and 0–100 μM with a limit of detection of 4.408 µM and 2.373 µM for Cu 2+ and L -Cys, respectively. All results indicate that P, Br-CDs are of great potential for further biological and environmental application.