Preparation Of Graphene Quantum Dots And Their Application In Cell Imaging

Graphene quantum dots(GQDs)is a new type of zero dimensional carbon-based nano fluorescence materials.Compared with organic dyes and semiconductor quantum dots,GQDs show many excellent physical and chemical properties,such as good water solubility,high fluorescence activity,fluorescence stability,dimensional stability,low toxicity and excellent cell compatibility,due to the obvious quantum confinement effect,edge effect and surface states.GQDs have great application prospects in cell imaging,analytical detection,drug delivery,photocatalysis and photoelectron fields.In this paper,we mainly studied the preparation of graphene quantum dots and their applications in the field of biological imaging and so on.Graphene oxide(GO)was used as carbon source,ethylenediamine as nitrogen source and reducing agent,hydrogen peroxide as oxidative cutting agent and alkaline environment was provided.The nitrogen doping GQDs(N-GQDs)were synthesized by top-down hydrothermal method.Transmission electron microscope(TEM),atomic force microscope(AFM),X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectrum(FTIR),ultraviolet-visible absorption spectrum(UV-Vis),photoluminescence spectrum(PL)and fluorescence lifetime system were used to characterize the structure,composition and fluorescence properties of N-GQDs.The average diameter of N-GQDs was 1.84 ± 0.28 nm,and the thickness of N-GQDs was also uniform,which was about 1 to 2 layers of graphene.The doping of nitrogen and reduction made the N-GQDs have excellent fluorescence properties,such as high fluorenscence intensity,high fluorescence quantum yield(QY=0.4758)and long lifetime(?=7.20 ns).Under the condition of p H=3.0-13.0 and[Na Cl]=0-1.0 mol/L,N-GQDs showed good fluorescence stability.The synthesis method was expected to realize the large-scale production of GQDs by top-down method.Further tests on N-GQDs showed that N-GQDs had good water solubility,low cytotoxicity,biocompatibility and cell imaing effect.We used CCK-8 kit to test the cell survival rate.Hela,Hep G2 and LO2 cells were cultured for 24 hours in the medium without and with N-GQDs.When the concentration of N-GQDs was lower than 100 ?g/m L,the cell survival ratio was more than 85%.The three kinds of cells were cultured with N-GQDs for 6h,and observed with confocal laser scanning microscope.The results showed that NGQDs had no obvious effects on the morphology and state of cells.The blue fluorescence could only be observed in the the cytoplasmic region.It can be seen that N-GQDs had broad development prospect in the biological imaging field.With citric acid used as precursor,urea as nitrogen source,phenylboric acid as boron source and water as solvent,boron and nitrogen co-doped GQDs(B,N-GQDs)were synthesized by bottom-up pyrolysis method.The structure and properties of B,N-GQDs were also characterized by TEM,FTIR,XPS,UV-Vis and PL spectra.The results showed that B,N-GQDs were successfully doped with boron and nitrogen and the partical size distribution of B,N-GQDs was uniform.The fluorescence intensity and fluorescence QY were also enhanced.The B,N-GQDs have great application potential in the field of cell imaging and tumor diagnosis and treatment.