Preparation And Performance Of Graphene Quantum Dot Based Materials For Cancer Cells Diagnosis

The preparation of fluorescent probe materials with biocompatibility and accurate recognition of cancer cells is one of the hotspots in the field of fluorescence diagnosis.The smaller size of graphene quantum dots is conducive to endocytosis and exocytosis of cells.Therefore,graphene quantum dots have great development prospects as fluorescent materials in the field of fluorescence diagnosis.GQD has "molecular-like" characteristics rather than colloids.This feature results in appropriate functionalization and tunable optoelectronic properties,both of which can promote their photoluminescence(PL)activity.In addition,their low cytotoxicity,higher solubility,chemical inertness,and surface grafting help graphene quantum dots have great applications in sensors,optoelectronics,or biological imaging.In addition,graphene quantum dots have good biocompatibility compared with other small molecular probe materials.Therefore,graphene quantum dots are selected as the base material of fluorescent probes.This paper focus on further expanding the application of graphene quantum dot as cancer cellfluorescence diagnostic materials.Due to the pathological effects of cancer cells,folate receptors,CD44,and cyclooxygenase-2 are overexpressed on their surfaces.This overexpression does not occur in normal cells,so folic acid,hyaluronic acid,and indomethacin can be used as targeting groups to achieve the purpose of accurate identification of cancer cells.In this paper,the synthetic graphene quantum dots were doped with nitrogen,and an amino group was introduced into the graphene quantum dots so that they could be combined with folic acid,hyaluronic acid,and indomethacin by amide bonds.Fourier transform infrared spectroscopy(FTIR),transmission electron microscopy(SEM),atomic force microscopy(AFM),X-ray photoelectron spectroscopy(XPS),and fluorescence spectroscopy(PL)were used to characterize nitrogen-doped graphene quantum dots and their combinations.In-depth analysis of the microscopic morphology,microstructure,and optical properties of the object proved that diagnostic materials for cancer cells were synthesized.Second,the combination of folic acid and nitrogen-doped graphene quantum dots,the combination of hyaluronic acid and nitrogen-doped graphene quantum dots,and the combination of indomethacin and nitrogen-doped graphene quantum dots were used as fluorescent diagnostic materials of cancer cells.After culturing,the conjugate was proved to have cancer cell diagnosis performance by laser confocal microscopy.Finally,the effects of incubation time,nitrogen doping content,pH value and other factors on the fluorescence diagnosis were explored.The content of this paper was divided into the following three aspects:1.The preparation and application of folic acid conjugated nitrogen doped graphene quantum dots as a fluorescent diagnostic material for breast cancer MCF-7 cells.Nitrogen-doped graphene quantum dots(N-GQD)were prepared by hydrothermal method using citric acid as carbon source and diethylamine as nitrogen source.The amount of diethylamine could effectively control the doping of different nitrogen contents.As the nitrogen content increased,more binding sites(N-H bonds)on the nitrogen-doped graphene quantum dots were supplied to the folic acid,and the XPS data indicated that the more nitrogen-doped content of the graphene quantum dots combined more folic acid.Laser confocal scanning microscopy showed that cells labeled with this material emitted stronger fluorescence.More folic acid combined promoted cancer cell recognition and swallowing,and thus cancer cells can be better detected.Cytotoxicity tests indicated that the material had low cytotoxicity,making it a promising prospect for fluorescent probes.2.Nitrogen-doped graphene quantum dots(N-GQD)could be easily prepared by hydrothermal method using citric acid as a carbon source and diethylamine as a nitrogen source N-GQD exhibited pH-sensitive properties in the range of 1.0 to 14.0,and the fluorescence intensity of N-GQD increased significantly with increasing pH.N-GQD were then bound to hyaluronic acid(HA)via an amide bond to recognize human breast cancer cells(MCF-7 cells).The combination of N-GQD with hyaluronic acid in different pH values environments had a certain effect on the formation of amide bonds.XPS and FTIR data showed that the formation of amide bonds was better promoted in alkaline environments,which was beneficial for N-GQD to bind more hyaluronic acid..Laser confocal scanning microscope obviously showed N-GQD-HA prepared under the condition of pH=14 had stronger fluorescence,which fully proved N-GQD-HA facilitated entry into cells through the endocytosis of cells.The results showed that hyaluronic acid combined with nitrogen-doped graphene quantum dots had good biocompatibility and development prospects in fluorescence diagnosis.3.N-doped graphene quantum dot conjugated indomethacin(N-GQD-IDM)was synthesized through amide reaction.FT-IR data indicated that the synthesis of N-GQD-IDM was successful.It was then co-cultured with MCF-7 cells and significant fluorescence was observed with a laser confocal scanning microscope.The effects of different incubation times on the diagnosis of cancer cells were subsequently explored.By comparing the pictures taken by the laser confocal microscope for 3 hours and 6 hours,it was shown that with the increase of the incubation time,a large amount of material was accumulated in the cells,and the fluorescence intensity of the cells was significantly enhanced.This showed that with the increase of incubation time,the cells continued to swallow N-GQD-IDM through endocytosis.Nitrogen-doped graphene quantum dot conjugated indomethacin could be used as a promising diagnostic material for cancer cells.