Hydrothermal synthesis of nitrogen and boron co-doped carbon quantum dots for application in acetone and dopamine sensors and multicolor cellular imaging

Nitrogen and boron co-doped carbon quantum dots (NB-CQDs) were prepared via one-pot hydrothermal treatment of citric acid, borax, and p-phenylenediamine. The synthesized NB-CQDs were characterized by transmission electron microscopy, Fourier-transform infrared spectra, X-ray photoelectron spectra, dynamic light scattering, ultraviolet-visible absorption and fluorescence spectra to characterize their surface morphology, crystal structure, functional groups and elemental composition, and optical properties. It was found that N and B species were efficiently doped into the carbon framework of the dots, the N -and B-Containing groups formed on the surface of NB-CQDs during the hydrothermal reaction. The element doping and surface functionalization of NB-CQDs efficiently modulated their physicochemical properties. The NB-CQDs were nearly mono-disperse with an average particle diameter of 3.53 nm, and the excitation/emission wavelengths were 360/490 nm, respectively. The NB-CQDs showed regular photoluminescence (PL) emission under different excitation wavelengths, and possessed pH-dependent and solvent polarity-dependent PL properties. In addition, the NB-CQDs and a NB-CQD/poly(vinyl alcohol) composite film showed good PL responses to acetone solution and vapor. A PL sensor for the determination of acetone solution with a limit of detection (LOD) of 0.54 mu M (R-2 = 0.9956) was then designed. The NB-CQDs were also used for the determination of dopamine. The PL intensity of the NB-CQDs was inversely proportional to the concentration of dopamine in the range of 0.1-70 mu M (R-2 = 0.9958). The LOD of dopamine was 11 nM, and PL quenching occurred via a static quenching mechanism. Additionally, these NB-CQDs can be used for multicolor cellular imaging and showed good uptake by Hepg2 cells.