Green Synthesis Of Heteroatom Doped Carbon Dots And Their Biological Applications

Scientists discovered a novel class of metal-free fluorescent nanomaterials,namely carbon dots in the year of 2004.Carbon dots have attracted much attention since discovered due to their low toxicity,environmental friendly,low cost and simple synthesis approaches.The unique optical and physicochemical properties of carbon dots have facilitated the development of new imaging probes and biosensing platforms.This thesis chose different green raw materials to obtain heteroatom doped carbon dots with excellent luminescent property through one-pot benign and simple synthesis route,and tested their applications in cell imaging as fluorescent probes.The main content of the thesis is as follows:（1）We used inexpensive and easily available vegetables（Chinese cabbage）as the materials to synthesize the nitrogen-doped carbon dots via one-pot hydrothermal method.The carbon dots were uniformly dispersed with the average diameter of 1.8 nm.They possess good luminescent performance and high quantum yield.The analysis of FT-IR and XPS showed that the surface of carbon dots were rich in-COOH,-OH and-NH₂ to enable the carbon dots with better water solubility.Metal ion response experiment demonstrated that the carbon dots could selectively detect copper ions without further modification.MTT results indicated the carbon dots were scarcely toxic.We observed the fluorescence images of Escherichia coli cells and HeLa cells after incubating with carbon dots using laser confocal microscopy.The imaging results confirmed feasibility of carbon dots as bioimaging reagents.（2）We synthesized nitrogen-and sulfur-co-doped carbon dots through one-pot simple and convenient hydrothermal carbonization approach with ginkgo leaves as the materials.We optimized the reaction temperature,and characterized the properties of carbon dots which were synthesized in optimized reaction conditions.TEM results displayed that the carbon dots we synthesized were with the average diameter of 2.22 nm and lattice spacing of 0.202 nm.FT-IR and XPS data revealed that the carbon dots were successfully doped with nitrogen and sulfur elements.When pH and ionic strength of carbon dots solutions changed,the fluorescence intensities of carbon dots were not changed significantly.In addition,we examined the cytotoxicity of carbon dots and discovered the cell viability was no obvious decrease.Finally,the carbon dots were applied to HeLa cells and KYSE410 cells imaging.The results indicated that the carbon dots synthesized by ginkgo leaves were appropriate for bioimaging as fluorescent probes.（3）We adopted microwave and hydrothermal methods respectively to produce heteroatom doped carbon dots using ginkgo fruit as the sole carbon source and double-distilled water as the solvent without additional surface passivation agents.The differences between these two products were compared in luminescence properties,particle sizes and morphologies.We found that the average diameter of microwave products was 2.82 nm with the lattice spacing of 0.23 nm while that of hydrothermal products was 3.81 nm with the lattice spacing of 0.21 nm.The TEM images showed that both microwave and hydrothermal products were well dispersed,and the morphology of hydrothermal products was more uniform.The fluorescence results indicated the hydrothermal products possessed better fluorescence emission characteristic.Thus,the hydrothermal carbon dots with better luminescence properties were characterized by TEM,FT-IR,XPS,fluorescence and UV-Vis spectroscopy.Also,we studied the stability and cytotoxicity of hydrothermal products synthesized by ginkgo fruit as the fluorescent probes.Eventually,we tested the application of the hydrothermal products in cell imaging using HeLa cells and KYSE410 cells as the cell models.