Phd Degree / Doktora

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Development of Colloidal Alloyed Nanocrystals for Quantum Dot Based Device Applications
(Izmir Institute of Technology, 2018) Sevim Ünlütürk, Seçil; Özçelik, Serdar; Varlıklı, Canan
Quantum dots (QDs) are very attractive luminescent semiconducting nanoparticles. In this study, our aim was to synthesize Cd and/or Zn based QDs with tunable optical properties by the particle size and the alloy composition. Colloidal water dispersible Mn-doped and nondoped ZnSxSe1-x QDs were synthesized by the one-pot aqueous method. Optical measurements indicate that photoluminescent properties are strongly depended on the capping agent. While MPA capped QDs showed an emission peak in the blue region, others did not show any photoluminescence at all. Mn doping up to 10% resulted in no significant effect on the optical spectra. However structural characterizations, EPR and XRD, supported that Mn ions were bounded to the 220 and 311 facets of QD. ZnxCd1-xSySe1-y quaternary nanoalloys were synthesized by using a modified two-phase approach for the first time in the literature. Optical properties of highly luminescent ZnxCd1-xSySe1-y nanoalloys were tuned from blue to yellow by the particle size, the alloy composition, and thickness of shell layer. The reactivity of the reactants, initial mole ratios, and other reaction parameters was adjusted to control alloy composition and alloy type: homogeneous and gradient. The reaction time controls the size of particles. The PL QE (up to 52%) and lifetimes (about 25 ns) were found similar regardless of core and core-shell nanoalloys. MicroPL measurements were carried out on ZnxCd1-xSySe1-y nanoalloys by fiber spectrometer integrated to confocal microscope. Photobleaching and blue-shifting, about 6 nm, were observed in the microPL spectra. Photobleaching times and rate constants obtained from single exponential decay curves showed that purification and exposure time are strongly effective. Additionally, the power the excitation light is essential that below 11 μW, photobleaching slows down, and at 2 μW there is no photobleaching. Scale-up methods with high-volume batch and flow reactor were used to synthesize CdTe and ZnxCd1-xSySe1-y QDs. LEFETs were fabricated with TUBITAK support in collaboration with Heidelberg University. PbS QDs were used as emitting material at the bottom contact top-gate unipolar LEFETs in which uniform electroluminescence was obtained.
The Effects of Engineered Silica Nanoparticles on the Cellular Behaviours of Human Hepatocellular Carcinoma Cell Lines
(Izmir Institute of Technology, 2018) Tüncel Çerik, Özge; Özçelik, Serdar; Atabey, Safiye Neşe
Physicochemical properties of the silica nanoparticles have vital roles in determining the physiological behaviours of the cells. Applications of nanoparticle treatments have some outcomes as a response of the cells in living systems as mitochondrial disruption, oxidative stress, reactive oxidative species (ROS) generation, altered cell cycle regulation and DNA damage. In this study 10 and 100 nm sized SiNPs were prepared and physicochemically characterized in the second part. Well characterized silica nanoparticles were used to assess the cytotoxicity and genotoxicity of the hepatocellular carcinoma cell lines as HuH-7 and SK-HEP-1 and lymphocytes. The cell cycle analysis was performed for engineered SiNPs to elucidate the DNA damage in the third part. In the fourth part mitochondrial responses of the cells were determined by real time confocal microscopy at single cell level. An image analysis method for evaluating the cellular responses by mitochondrial staining was developed. DCF stained cells were analyzed in order to assess the production of ROS in the cells. Localization of the SiNPs were determined by lysosomal and mitochondrial staining. Pearson correlation coefficients of the images were used for evaluating the colocalization of organelles with SiNPs. Lastly, diffusion coefficients of the SiNPs in the cells were determined by quantitative confocal microscopy. The SiNPs were found as non-toxic up to 200 μg/ml for 5 days. The SiNPs did not induce the formation of micronuclei in lymphocytes. The SiNPs were not cause an arrest in cell cycle progression. Mitochondrial potentials were not changed after SiNP exposure as well. They were mostly internalized at 30 minutes in both cell line in lysosomal parts without increasing ROS in the cells. It can be concluded that the SiNPs can be safely used for targeted delivery of organic compounds, biological molecules or drugs in medicine, and may be utilized as a probe system in biological studies.

Phd Degree / Doktora

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