Synthesis And Biomedical Applications Of Novel Heteratoms Doped Carbon Dots

Carbon dots(CDs)is a rookie in the carbon nanomaterials family.The size of CDs is generally less than 10 nm,mainly using sp2 hybrid conjugated carbon as the core,with a large number of organic groups containing oxygen or other heteratoms on the surface,which is like a"core-shell"structure.In addition to good optical properties such as high fluorescence quantum yield,good fluorescence stability,and photobleaching resistance,the CDs have many excellent properties,such as facile surface modification,low toxicity,good biocompatibility and low preparation cost.In recent years,within the gradual deepening of research on CDs,its application fields have been continuously expanded.At present,carbon dots have been widely used in the fields of photocatalysis,bioimaging,photodynamic therapy and photothermal therapy.In this thesis,we synthesized copper-doped carbon dots by polyacrylic acid in-situ polymerization carbonization method,and explored the application of the carbon dots in bioimaging and photodynamic therapy.The organic molecules were used to synthesize fluorine and nitrogen co-doped carbon dots by a microwave synthetic method,which can complex with iron ions to form a stable complex.The magnetic relaxivity,cytotoxicity of the complex and its application as a contrast agent in magnetic resonance imaging(MRI)were studied.Additionally,using a natural polymer as the carbon source,the amphiphilic CDs were fabricated by pyrolysis with a good cell imaging effect,and the ability of the carbon dots and inorganic semiconductor nanocomposites to catalyze the degradation of organic pollutants under ultraviolet-visible-near infrared irradiation was also evaluated.The main research contents and results of the paper are as follows:1.A complex of copper and polyacrylic acid was prepared by in-situ polymerization using a complex of acrylic acid and copper nitrate as a precursor.Then using the as-prepared complex as precursor,copper-doped carbon dots(Cu-CDs)were synthesized by pyrolysis method(400 ?,90 min).The morphology,structure and fluorescent properties of the obtained Cu-CDs were characterized by transmission electron microscope(TEM),X-ray photoelectron spectroscopy(XPS),,ultraviolet-visible absorption spectroscopy(UV-Vis),fluorescence spectroscopy(PL),etc.,it is found that:(1)The copper doping amount of Cu-CDs is 0.51 At.%(atomic ratio),and the carbon core have a graphitized crystal structure with an average particle diameter of 2.8 nm.(2)The aqueous solution of Cu-CDs emit bright green fluorescence under ultraviolet light and the fluorescence emission behavior has excitation-dependence.The research of Cu-CDs applied in bioimaging and photodynamic therapy is as follows:(1)HeLa cells(human cervical cancer)were used as two-dimensional(2D)cell model and SH-SY5Y(human neuroblastoma cells)multicellular spheroids were used as three-dimensional model(3D MCs).The cell imaging effect of Cu-CDs was observed by fluorescence microscopy and confocal laser scanning microscopy(CLSM).The results show that both 2D cells and 3D MCs exhibit bright green fluorescence under 405 nm laser excitation,indicating that Cu-CDs have good cell imaging effect.(2)The electron spin resonance spectroscopy(ESR)was used to qualitatively study the ability of Cu-CDs to generate singlet oxygen(1O2)with LED light irradiation.The results show that Cu-CDs have stronger signals of 1O2 than CDs,and both of the 1O2 induced by CDs and Cu-CDs are concentration dependent.(3)Using Rhodamine B(RB)as a reference and 9,10-anthracenediylbis(methylene)dimalonic acid(ABDA)as a capture agent,UV-Vis absorption spectrum was used to quantitatively characterize the ability of light-induced Cu-CDs to produce 1O2,and 1O2]yield was calculated to be 36%.(4)HeLa cells were selected as a cell model,and the viability of HeLa cells with different concentrations of Cu-CDs under the same irradiation conditions and the same concentration of Cu-CDs under different irradiation time was detected by MTT method(tetramethylazozolium salt colorimetric method).The MTT results show that the cytotoxicity of Cu-CDs is concentration-dependence under the same irradiation,and the longer the irradiation time lasts,the lower viability of HeLa cells co-incubated with Cu-CDs.Cu-CDs were also found to be more effective in inhibiting the growth of 3D MCs under light conditions.The above results indicate that Cu-CDs with both cell bio-imaging and photodynamic therapy functions have been successfully synthesized.2.Using glucose as the carbon source and levofloxacin as the dopant,the fluorine and nitrogen co-doped CDs(F,N-CDs)are successfully synthesized.The morphology,structure and fluorescence properties of the F,N-CDs were characterized by TEM,XPS,UV-Vis absorption spectroscopy and PL spectroscopy,it is found that:(1)The average particle size of F,N-CDs is 1.68 nm,The inside is a crystalline carbon core with a large amount of organic groups containing F,N and O on the surface,wherein the nitrogen doping amount is 8.3 At.%(mainly in the form of pyridinic-nitrogen,pyrrolic-nitrogen and graphitic-nitrogen).The fluorine doping amount is 3.3 At.%,mostly in the form of C-F bond and the oxygen doping amount is 22.65,exists in the form of hydroxyl and carboxyl groups.(2)F,N-CDs have a good hydrophilicity,bright green fluorescence under ultraviolet light and high absolute fluorescence quantum yield(QY=22.98%).(3)F,N-CDs have good ion selectivity and can form a stable complex with Fe3+(Fe3+@F,N-CDs,the complexation constant is as high as 1.06 ×107).When the complex concentration of Fe3+ is lower than 0.3 mM,the complex still shows strong green fluorescence.The magnetic relaxivity,cytotoxicity and application in MRI of Fe3+@F,N-CDs were studied as follows:(1)It was measured on a 1.5 T nuclear magnetic resonance analyzer(NMR),Fe3+@F,N-CDs have a high longitudinal relaxivity(rt=5.79 mM-1·s.1).This value is comparable to the ri\value of the commercial contrast agent such as Gd-DTPA.(2)Using HeLa cells as a cell model,the MTT results show that F,N-CDs have low cytotoxicity.More importantly,Fe3+@F,N-CDs also shows low cytotoxicity.(3)Using HeLa cells as a cell model,it was measured on a 1.5 T NMR analyzer that Fe3+@F,N-CDs show a low longitudinal relaxation time(T1 and good in vitro cell MRI effect.(4)4T1 cells(mouse breast cancer cells)were used as tumor models,and were inoculated into the hips of Balb/c mice to construct an animal model.The distribution,accumulation and metabolism of the materials in mice were studied by a 1.5 T NMR analyzer.The MRI studies of animals were performed on a 3.0 T NMR analyzer.The results show that Fe3+@F,N-CDs can be rapidly enriched in the liver and tumor of mice in 15 minutes,and exhibits a good MRI effect.In addition,using HeLa cells as a cell model,the cell imaging effect of Fe3+@F,N-CDs was studied,and the results of CLSM show that the cell imaging effect of Fe3+@F,N-CDs are slightly inferior to F,N-CDs,but still better than CDs and Fe3+@CDs,indicating that Fe3+@F,N-CDs are possible to be used for magnetic resonance/fluorescence dual-modal imaging.3.Using natural polymer-corncob as a carbon source,the amphiphilic carbon dots(C-CDs)with both hydrophilic and lipophilic groups were obtained by pyrolysis(350 °C,90 min)in an air atmosphere.The morphology,structure and fluorescence properties of the carbon dots were characterized by TEM,XPS,UV-Vis absorption spectroscopy and PL spectroscopy,it is found that:(1)The average particle size of C-CDs is 2.48 nm,and the oxygen doping amount is as high as 22.48 At.%,mainly in the form of hydroxyl groups,carboxyl groups and polymer residues.(2)Using quinoline sulfate as reference solution,the average QY(relative fluorescence quantum yield)of C-CDs in water is as high as 61%.(3)The PL of the C-CDs aqueous solution has excitation-dependence,concentration dependence and pH dependence,and is selective for Fe3+ ions,which can be used for metal ion fluorescence detection.The following application studies were conducted on C-CDs:Using HeLa cells as a cell model,it can be observed from CLSM that C-CDs emit bright fluorescence irn cells under different laser excitation,showing a good imaging effect.Additionally,the nanorods composited with C-CDs and Bi2S3 were synthesized,which is a full spectrum photocatalyst.The above results show that C-CDs made from natural polymers are not only a good metal ion detection agent,but also a good cell imaging agent.They can also be combined with inorganic nanomaterials for photocatalytic degradation of organic pollutions in water environment.