Synthesis, Properties And Biolabling Application Of Strong Fluorescence Quantum Dots

Fluorescent quantum dots (QDs) have promising prospect in photoelectronic devices and biomedical fields due to their unique optical and electrical properties. The premise of further development and application of QDs in biomedical fields lies in their excellent optical properties, favorable biocompatibility and accurate biological targeting ability. To fulfill above objectives, it is necessary to choose and design the ligand on surface of QDs to increase the fluorescence, decrease the toxicity and enhance the targeting recognition. Besides, to search some new quantum dots with biocompatibility and environmental friendly properties to replace traditional semiconductor QDs is an alternative approach, such as carbon dots, silicon QDs, and InP QDs, etc. According on above two ideas and based on research on abundant of literature about fluorescent QDs, this dissertation carried out some works focus on following aspects:First, designed and synthesized water-soluble cadmium sulfide QDs which had unique optical properties and biological targeting properties; studied fluorescent mechanism of the QDs and carried out cell labeling experiment to demonstrate its targeting ability. Second, investigated the fluorescence of newly emerged carbon dots (CDs); arose a chemical reduction method which was efficient to increase the fluorescence quantum yield of CDs and studied the mechanism of fluorescence enhancement. Last, carried out works about aqueous g-irradiation effects on CDs and arose an alternative scheme to achieve fluorescence enhancement or rapid degradation of CDs by controlling of aqueous irradiation environments. The main research results of this dissertation are listed below:1) Designed and synthesized a ligand (TA) containing1,2,3-triazole rings and then synthesized aqueous cadmium CDs (TA-QDs) accordingly. TA-QDs have two fluorescence emission peaks on540nm and650nm, which originated in cadmium sulfide nanocrystalline itself and complex which constructed through surface coordination effect by TA and QDs, respectively. On protection of ligand, the fluorescence of TA-QDs could keep stable on different ionic strength and broad pH values. We investigated the coordination effect between TA and QDs via XPS, Raman and1H NMR and demonstrated the1,2,3-triazoles and Cd(Ⅱ) cations could form the complex via electrochemical analysis method. The ethidium bromide exclusion assay demonstrated that the ligand strongly interacted with DNA.Cell labeling experiment showed that TA-QDs could selectively label the nucleolus of cancer cells and had strong targeting effect.2) Developed a facile and effective NaBH4chemical reduction method to dramatically enhance the fluorescence intensity of CDs without any surface modification. The quantum yield of reduced CDs could reach up to16%. Combined with hydrothermal method, the NaBH4reduction method could further increase the quantum yield of CDs to more than40%.13C NMR, Raman, and XPS analysis results showed that the carbonyl groups were reduced to hydroxyl groups on surface of CDs and the surface defect increased under NaBH4treatment. Then the number of non-radioactive recombination center also decreased. Besides, XPS results also showed that the value of VBM of CDs kept decreasing elongate with reduction time. The band bending degree on surface of CDs increased. The decreasing number of non-radioactive recombination center and increasing degree of bend bending of CDs were the two reasons for its fluorescence enhancement.3) Investigated the effect of aqueous y-irradiation method on CDs. We found that γ-irradiation could lead totally different effect to CDs in different reductive environments. When irradiation happened in pure water, CDs could be eliminated quickly and the fluorescence could be totally quenched with it. Nevertheless, when radical scavengers were added to create reductive environment in aqueous irradiation systems, CDs could not be eliminated under15kGy irradiation dosages. What’s more, the fluorescence of CDs could be dramatically enhanced in this environment.