Microwave Heating Fluorescent Carbon Nanoparticles Synthesis, Characterization And Application In Cell Imaging

Due to the complex preparation, instability, easy photo-bleaching and generally poor biocompatibility of traditional organic fluorescent dyes, their wide application was limited. Compared with traditional organic fluorescent dyes, fluorescent nanomaterials has overcome these disadvantages, and widely been used in optoelectronic devices, biological markers, bio-pharmaceuticals, catalysts, and other fields. The most popular fluorescent nanomaterials are quantum dots, a kind of semiconductor nanoparticles, with unique optical properties and electrical characteristics. However, there are toxic elements in quantum dots, which will harm the environment, affect the activity of cells or biological macromolecules. On the other hand, the quantum dots show larger size and light flicker.Carbon is a unique material. It is a good conductor in graphite morphology, a wide-gap-semiconductor in diamond morphology, and a kind of polymer when it reacts with hydrogen. carbon shows all performance of nanomaterials, such as fullerenes, carbon nanotubes, graphene, carbon nanofibers and nanodiamond. In recent years, carbon is widely studied in chemistry, material science, biology and physics and so on. Fluorescent carbon nanoparticles, new members of the family of carbon nanomaterials, have semiconductor quantum size effect and upconversion fluorescence properties of light-emitting nano-materials. They own some advantages, such as various preparation methods, monodispersity, small particle size, good solubility in water and easy surface functionalization. In addition, good biocompatibility and low toxicity of carbon nanoparticles make it be an alternative of quantum dots. Carbon nanoparticles with unique performance can be widely used in analysis, light-emitting devices, biological imaging and catalysis.Now there are a large number of reports on the preparation and application of fluorescent carbon nanoparticles. But most of the preparation methods are tedious and complex, and show a relatively low fluorescence quantum yield. Passivation and doping are popular approaches to enhance their fluorescence quantum yield, but they are time-consuming and expensive. Finding an effective method for preparation and modification of carbon nanoparticles with improved fluorescence quantum yield is very meaningful. For this reason, this paper mainly focuses on the preparation and application of fluorescent carbon nanoparticles. The aim is to explore a simple, fast and inexpensive method for synthesis of fluorescent carbon nanoparticles and improve their fluorescence property by a simple, green and effective modification approach.The thesis included two parts:review and research work. First part is the review, including a brief overview of the nanomaterials; the various preparation methods, properties and relevant applications of fluorescent carbon nanoparticles, microwave heating characteristics, and finally the research purpose and content of this thesis. The second part is the research report, divided into two parts:1. In order to prepare carbon nanoparticles with perfect fluorescent performance, different carbohydrates were used as carbon source, polyethylene glycol200(PEG-200) as passivation agent, and microwave as a heating method. Compared with other carbon sources, carbon nanoparticles produced from vitamin C have the best fluorescence performance. Compared with the conventional heating method, microwave heating method has some advantages, for example, short time, quick microwave reaction, uniform heating, and small temperature gradient. The formation of carbon nanoparticles takes a short time during dehydration, aggregation, pyrolysis, caramelization and surface passivation, while introducing more oxygenated groups on carbon nanoparticles surface. The size of carbon nanoparticles obtained by microwave heating is about5nm. They emit blue light and have good fluorescent performance, low photobleaching effect and good resistance to salt. They can be used as fluorescence probes in cell imaging and targeting tracer.2. A simple surface modification method to improve fluorescence properties of carbon nanoparticles was developed. At room temperature, the carbon nanoparticles obtained by microwave heating vitamin C and PEG-200solutions were oxidized by hydrogen peroxide in water phase. The method is simple and quick. The used reagents are cheap, green and without further purification. Compared to ordinary carbon nanoparticles, the modified ones can maintain their size, shape and monodispersity. However, the fluorescent performances of the oxidized carbon nanoparticles were significantly improved. They have stronger fluorescence emission and higher fluorescence quantum yield. Due to their good fluorescent properties, oxidized carbon nanopartiles can be used for cellular imaging. Because of the small particle size of carbon nanoparticles, they can be endocytosis into cells, mainly exist in the cytoplasm and cell membrane.