Solid-phase Synthesis And Application Of Doped Carbon Quantum Dots

As newcomers to the nanomaterials family, carbon quantum dots (C-Dots) have attracted tremendous attention, owing to their remarkable advances in high resistance to photobleaching, robust chemical inertness, low toxicity, and good biocompatibility. The preparation and application of C-Dots have recently attracted more attention in analytical chemistry. However, the research on C-Dots is still at its early stage. There are still some issues needing to be solved, such as the low product yield and quantum yield, the deficiencies in accurately controlling lateral dimensions as well as surfaces chemistry, the confusing PL mechanism, the narrow spectral coverage, the lack in tailormade control of optical properties, etc. Therefore, there is a huge development space for C-Dots. To accurate control of lateral dimensions and the surface chemistry of fluorescent C-Dots, as well as with high quantum yield (QY) and product yield, and to study on its applications in biological chemistry, the following major innovative researches were carried out in this thesis on the basis of the previous works.1. A new solid-phase synthesis method was developed for preparation of N-doped C-Dots. The QY was markedly improved. And the N-doped C-Dots was successfully applied for imaging of Fe3+ in living cells.2. By using N-doped C-Dots as a fluorescent probe, a new method for fast and sensitive detection of tartrazine was established. The method was subsequently applied for the determination of tartrazine in fruit juice, fruit drinks, fruit beer and jam for the first time.3. A solid-phase synthesis strategy was established for the preparation of sulphur doped fluorescent carbon nitride quantum dots (g-CNSQDs). The as-prepared nanomaterial has good stability, water solubility and biological compatibility, and has been successfully applied for cell imaging.4. By using g-CNSQDs as fluorescent probe, a new approach for selective and sensitive detection of Hg2+ was established. The method was applied for the detection of Hg2+ in real samples with satisfactory results.This dissertation consists of six chapters.Chapter 1:The aspects of synthetic approaches, optical properties and present applications, especially in bioimaging and sensors were reviewed.Chapter 2: A facile and high-output solid-phase synthesis approach was proposed for the fabrication of highly fluorescent N-doped C-Dots. Owing to fluorescence enhancement effect of introduced N atoms into carbon dots, the absolute quantum yield (QY) of N-doped C-Dots was up to 31%. The strong coordination of oxygen-rich groups on N-doped C-Dots to Fe3+ caused fluorescence quenching via nonradiative electron-transfer, leading to the quantitative detection of Fe3+. Significantly, the N-doped C-Dots possess negligible cytotoxicity, excellent biocompatibility, and high photostability, and were successfully applied for the fluorescence imaging of intracellular Fe3+.Chapter 3:Based on the effective quenching effect of N-doped C-Dots, a new method for fast and sensitive detection of tartrazine was established. The method was subsequently applied for the determination of tartrazine in fruit juice, fruit drinks, fruit beer and jam for the first time. The fluorescence quenching was probably ascribed to the strong inner filtering effect (IFE) and molecular inter-atomic forces between N-doped C-Dots and tartrazine. The proposed method is simple, rapid, sensitive and reproducible. It is expected to replace the current detection methods for tartrazine monitoring in fruit products and provides a new choice for food safety purpose.Chapter 4:For the first time, a solid-phase synthesis method was proposed for preparation of g-CNSQDs nanomaterials. The morphology and properties of g-CNSQDs were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible absorption spectroscopy (UV-vis), fluorescence spectroscopy and time-resolved fluorescence spectroscopy. The influence of raw material ratio on the fluorescence properties was investigated. The g-CNSQDs possess good stability, water solubility and biological compatibility, and have been successfully applied for cell imaging. It holds great promise in optoelectronic devices, sensors, drug/gene carrier and other biological applications.Chapter 5:Based on the strong quenching effect of Hg2+ on g-CNSQDs, a new sensitive method of rapid detection of Hg2+ in aqueous solutions was established. The factors that affected the fluorescence quenching efficiency and its feasibility for real samples analysis were evaluated. Results showed that the method is simple, rapid, sensitive, and reproducible, and has been successfully applied for the detection of Hg2+ in tap water and Yellow River water, which expands the application of g-CNSQDs in bio-analytical chemistry.Chapter 6:Conclusion.