Studies On The Synthesis Of N-Doped Fluorescent Carbon Dots And Their Applications In Cellular Imaging And Pharmaceutical Analysis

Carbon dots, a sort of novel fluorescent carbon nanomaterial, have attracted tremendous attention due to their good optoelectronic properties and biocompatibility and have good potential in bioimaging, pharmaceutical analysis and many other fields. However, there still remain some main problems in the preparation and application of CDs. For example, most of CDs show very low quantum yields and short emssion wavelengths in blue light region, which is similar to the fluorescence of biological samples and limits the applications in bioimaging. Therefore, researchers are faced with enormous challenges in improving the quantum yield of carbon points, and broaden their applications. In this thesis, we embarked from the selecting of raw materials and preparation of CDs, have successfully synthesized CDs with different characteristics through doping of nitrogen, investigated the applications in bioimaging and further explored their application in pharmaceutical analysis and some other fields. The main contents of the thesis were listed as the following two parts:（1） One-pot hydrothermal synthesis of nitrogen-doped carbon dots from methionine for bioimaging.We chose methionine as raw material to prepare CDs through one-pot hydrothermal method in this thesis. The as-prepared CDs were co-doped with nitrogen and showed excellent optical properties. Transmission electron microscope（TEM） results showed that CDs were spherical with uniform average diameter about 5 nm. The XPS, FTIR and Raman results implied that CDs contained carbon, nitrogen, oxygen, sulfur elements and existed rhydroxyl, carboxyl, amino groups on the surface, which made them have good water solubility. The CDs had good photoluminesce properties with maximum excitation wavelength at 330 nm and maximum emission wavelength at 405 nm. In addition, the excellent photostability make the fluorescent intensity hardly show any change even the CDs in acid, alkali and high ionic strength solution. The CDs could enter and light up cells with their low biotoxicity and excellent biocompatibility, and have good potential as a biological imaging agent.（2） Hydrothermal synthesis of highly luminescent nitrogen-doped carbon dots from silk and their application reserch.In this paper, natural silk were used as raw material with high nitrogen content to synthesize CDs through hydrothermal method, the as-prepared CDs emitted blue fluorescence and of high quantum yield up to 61.1%. TEM and AFM results showed that CDs were spherical with uniform average diameter about 5.6 nm. The FTIR, and Raman XPS results implied that CDs contained carbon, nitrogen, oxygen elements and existed rhydroxyl, carboxyl, amino groups on their surface. The CDs possess unique optochemical stability even in high ionic strength solution or most organic solvent. Therefore, based on fluorescence quenching of CDs through the interactions between Fe³⁺ and the surface hydroxyl groups, thus established a method for the detection of Fe³⁺. Secondly, CDs were loaded in electrospun nanofibers in order to broaden the application, and we hope it can be used in solid sensors in the future. Finally, we established a probe by using MnO2 nanosheets and CDs, and it can be applied for detection of glutathione based on fluorescence resonance energy transfer.The studies above showed that the CDs prepared from methionine were doped with nitrogen. The CDs have been successfully applied in bioimaging due to their excellent photoluminescent properties and low biotoxicity, which broaden the range of raw materials for preparation of CDs. CDs with high fluorescence quantum yield from silk and citric acid can be used for the detection of Fe³⁺ and glutathione by constructing a probe, which broaden the scope of application of the CDs. In addition, the preparation of the CDs were rapid, simple and can be prepared in large scale.