DMSA?nın bozunumu sayesinde suda yapılan CdS ve CdTe/CdS kuantum noktacıklarının geliştirilmesi

Quantum dots (QDs) have attracted great interest and gained significance in many research areas of science and technology due to their unique chemical and physical properties. The most striking property of these semiconductor nanocrystals is the size-dependent absorbance and emission spectra as a result of quantum confinement. Moreover, they have high quantum efficiencies, narrow and symmetric emission spectrum, wide optical absorption bands, long fluorescence lifetime in comparison with organic fluorophores and compatibility with organic solvents and biological media. This M.S. thesis mostly concerns about the applications of quantum dots in biotechnology and medicine.The research of this thesis aims at developing highly luminescent, colloidal aqueous quantum dots which are applicable to biological systems. In order to achieve this goal, DMSA (meso-2,3-dimercaptosuccinic acid) was chosen as the stabilizer (surfactant), which is known to be bio-compatible. In the first step, CdS QDs were prepared by a very simple experimental strategy. Effects of reaction temperature, pH and DMSA amount on particle size and quantum yield (QY) were examined. As a result, DMSA was used both as a stabilizer and a sulphur source in the synthesis of colloidal, highly stable aqueous CdS QDs. Particles luminescing from blue to orange with QY values of 8-10 % were obtained at pH 7.5 and 70ºC. In these syntheses, SH (DMSA)/Cd ratio of 2.7 was determined as the optimum ratio providing highest QY.The second step was the fabrication of 2-mercaptopropionic acid (2-MPA) capped CdTe/CdS core/shell QDs by the decomposition of DMSA. The shell growth improved the optical quality of CdTe core significantly. Three important reaction parameters (SH(DMSA)/Cd ratio, initial pH and SH(2-MPA)/Cd ratio) were investigated. Consequently, CdTe/CdS core/shell QDs luminescing from green to red were accomplished with a maximum QY of 73.3% by the decomposition of DMSA without any post-preparative method. Optimum reaction conditions were initial pH of 7.5, Cd2+:Te2-:SH(2-MPA) ratio of 1:0.38:2.4 and Cd2+:SH(DMSA) ratio of 1:0.7. Besides, DMSA was compared with a common sulphur source, thioacetamide (TAA), and much better luminescence compared to TAA case was obtained with the DMSA. Results indicate that DMSA acts both as a sulfur source for the shell growth and as a co-surfactant which improved both optical properties and long-term stability of particles. Shell growth removes surface defects and therefore radiative coupling events were supported. This is shown by increasing luminescence lifetimes (both short and long-lifetime components) and increasing weight of the surface related emission lifetime values.Overall, the research summarized in this thesis elucidates the dual action of DMSA (capping agent and sulfur source) in CdS QD synthesis and further proves the effectiveness of DMSA in the formation of colorful, stable and highly luminescent CdTe/CdS core/shell QDs. Considering the simplicity of the synthesis method and the biocompatibility of DMSA, the information and materials prepared here should be valuable for biotechnology and medical research.