Browsing by Author "Özçelik, Serdar"

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A computational study of excitation dynamics on semiconductor surfaces
(Izmir Institute of Technology, 2019-12) Kaya, Birnur; Sevinçli, Haldun; Özçelik, Serdar
Recent experimental studies have shown that collodial quantum dots can be produced in large quantities and their optical properties can be tailored by controlling their composition, size and surface characteristics. Motivated by these studies, this thesis is devoted to the investigation of excitation dynamics on semiconductor surfaces, which are passivated with organic molecules. First, constructing a simplified model, excitation dynamics is investigated by computing time dependent occupations of frontier molecular orbitals for various scenarios regarding the values for the energy gap between the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO), as well as the coupling strengths. Second, the model is enhanced to address realistic systems. Passivation of ZnS surface with oleic acid (OA) is modeled using density functional theory based tight binding (DFTB) simulations. Extracting the Hamiltonian and overlap matrices, excitation dynamics is studied for Zn rich and S rich surfaces and different coverage ratios of surfaces. The excitation dynamics is compared and contrasted against the simplified model. Characteristic features are identified and typical decay rates are calculated for various molecular configurations. In addition to these, X-Ray diffraction spectra of quaternary ZnCdSSe nanoalloys have been investigated.
Development of a novel electrocardiography sensor based on a composite silver chloride nanoparticles and polyaniline
(Izmir Institute of Technology, 2013) Taşcıoğlu, Didem; Özçelik, Serdar
The electrical activity of the heart is detected by electrodes attached to the surface of the skin. These electrodes detect bioelectrical signals in the human body. Physilogical status of heart condition especially cardiovascular diseases and disturbances in the cardiac rthym are recorded by electrocardiography (ECG). Despite the fact that the usage of disposable ECG electrodes in our country is substantial nearly as 70 million in 2010, these electrodes are not fabricated in Turkey. In the scope of this study, it was aimed to develop a novel sensor based on synthesized AgCl/Polyaniline nanocomposites for ECG electrodes. In this study, the production of silver chloride (AgCl) nanoparticles was achieved by the polyol method. ABS (Acrylonitrile butadiene styrene) was used as a supporting material of the ECG electrode. Synthesized AgCl nanoparticles were not easily adsorbed on the surface of ABS. We develop a synthetic chemistry to perform simultaneous synthesis of AgCl nanoparticle and polymerization of aniline on surface of ABS. Polyaniline acts as a chemical linker between the nanoparticle and ABS surface in the same batch reactor. The synthesized composite based on polyaniline and AgCl nanoparticles completely covers the surface of ABS. To evaluate electrodes, we fabricated a disposable ECG electrode and compared it with the disposable electrodes that are commercially available. The electrocardiography data indicated that the fabricated electrodes were demonstrated a performance which is comparable with the commercial electrodes. The results demonstrate that a novel ECG electrodes can be manufactured based on this new composite material and method develop in our laboratory.
Development of colloidal alloyed nanocrystals for quantum dot based device applications
(Izmir Institute of Technology, 2018-06) 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.
Development of copper and manganese doped ternary colloidal quqntum dot alloys
(Izmir Institute of Technology, 2019-01) Yırtıcı, İlayda Melek; Özçelik, Serdar
Semiconductor nanocrystals have great interest due to their unique optical properties such as the particle size and the alloy composition dependent spectra, photochemical and colloidal stability. They have wide range of potential applications like solar cells, light emitting diodes (LED) and bioimaging etc. In this thesis, colloidal ternary Cu doped and undoped ZnSxSe1-x nanoalloys were synthesized by modified one pot aqueous approach. TGA and MPA ligands were used as capping agents for the synthesis of ZnSxSe1-x and Cu doped ZnSxSe1-x colloidal nanoalloys. The results showed that capping agents have an significant effect on optical properties of ZnSxSe1-x nanoalloys. Although the TGA capped nanoalloys have well-defined absorption bands rather than MPA capped ones, ZnSxSe1-x nanoalloys with TGA capping agent fluorescence peak was not observed. Therefore, the further study was continued with MPA capped ZnS xSe1-x ternary nanoalloys. Optical spectra demonstrated both absorption and PL spectra were shifted due to the adding of Cu dopant. Absorption peak shifted from 335 nm to 376 nm. Fluoroscence spectra also was redshift from 469 nm to 565 nm. Thus, we can conclude that, colloidal ternary nanoalloys optical properties can be tuned by using chemical doping. On the other hand, the optical and structural properties of binary ZnSe QDs, Mn and Cu doped ZnSe nanocrystals were investigated. We concluded that ZnSe and ZnS xSe1-x nanocrystals can be used to synthesize doped nanocrystals by chemical doping. We demonstrated that optical and structural properties of Cu and Mn doped ZnSe can be tuned by chemical doping.
Development of fluorescent carbon-dots for biological imaging
(01. Izmir Institute of Technology, 2021-12) Kavuranpala, Tuğçe; Özçelik, Serdar
Carbon dots are called carbon quantum dots or carbon nanoparticles (NPCs), and their use has recently started to increase thanks to their good biocompatibility, unique optical properties, easy synthesis, and low toxicity. Different kinds of carbon sources and amine sources also used as different dopes of chemical create a different emission color of CDs under UV-lamp. In this study, our aim to provide a simple synthesis of carbon dots with high quantum efficiency and low toxicity for use in cell imaging. Nitrogen and sulfur-doped carbon dots were synthesized using citric acid and thiourea, and emission was obtained in the blue-green region. After the synthesized carbon dots were seeded to the A549 cell culture, intracellular viability and cell toxicity results showed that carbon dots did not affect cell viability at certain concentrations. Afterward, the carbon dots are combined with gold nanoparticles and it is aimed to attach the gold to the surface of the carbon dots. Our aim here is to increase the efficiency of carbon dots, which give an emission peak at 550 nm, thanks to gold nanoparticles. As a result of these studies, it was proved by DAPI staining that the carbon dot is directed to the nucleus of the cell. Since it does not create a toxic effect and is transported to the cell nucleus, it allows it to be used in intracellular drug transport and imaging processes in the next stages.
Development of mitochondria targeted gold nanorods
(Izmir Institute of Technology, 2019-12) Uçak, Hande; Özçelik, Serdar
Lung cancer has the largest number of lives for the global pattern of cancer death. However, the percentage of the cancer treatment is too low. Gold nanoparticles have a widely range in terms of biomedical applications in diagnosis, imaging because of their unique optical properties, simple synthesis techniques, biocompatibility and suitable for easy surface change. Redox reactions in the mitochondria generates a potential called as mitochondria membrane potential. The aim of the study is to design mitochondria targeted gold nanorods and to observe how the designed gold nanorods effects the mitochondria membrane potential by targeting the mitochondria on A549 and BEAS-2B cell lines. Gold nanorods were utilized by seed growth mediated method and the surface bioconjugation was performed with triphenyl phosphonium cation as a mitochondria targeted molecule. Poly (sodium-p-styrene sulfonate) was used to prevent aggregation during the bioconjugation process. Gold nanorods which had 30 nm x 10 nm in length and diameter depending on SEM images had well-defined absorption bands 513 nm and 774 nm in wavelength. Mito-pot analysis with the fluorescent intensity ratio and colocalization analysis with light intensity for targeting gold nanorods to mitochondria showed that the accumulation on mitochondria for TPP-GNR was higher than PSSGNR. TPP-GNR was more toxic than PSS-GNR for both of cell lines by investigations of MTT viability test. TPP-GNR targeted to mitochondria and it affected fundamental cellular functions in mitochondria. To concluded that accumulation on mitochondria was accomplished for TPP-GNR and the decreasing of mitochondria membrane potential was observed on this study.
Development of novel anticounterfeiting technologies using heavy metal free nanoparticles
(Izmir Institute of Technology, 2021-07) Taşcıoğlu, Didem; Özçelik, Serdar; Demir, Mustafa Muammer
Counterfeiting, the act of illegally copying a product, document or currency, is a growing problem and causes economic losses. Anticounterfeiting technology uses fluorescent inks that are invisible to the naked eye in daylight, but become visible under UV light. However, these inks have problems such as fading when exposed to sunlight or room light for a long time and disappear completely over time. This is due to the relevant inks are made using organic dyes that fade. The inks used in anticounterfeiting application preventing copying of secure documents such as banknotes, passports and ID cards must be health-friendly and chemically and optically stable for years. All of the existing security materials and equipments for ID cards, driver's licenses, passports, banknotes used in our country are imported. In this study, our aim is to create a new generation of security materials and codes to combat counterfeiters and to verify the generated security codes in a simple, efficient and fast way. In this study, it is aimed to produce nanoparticles, which do not contain heavy metals and show optical stability for a long time, emitting in visible region, on the basis of the security codes created. For this purpose, water and solvent-based nanoparticles synthesized which are non-toxic should have a long-term optical stability. The synthesized nanoparticles act like a pigment in security codes. The photoluminescence (emission color) of the security codes can be adjusted by size and chemical composition of nanoparticles. In this study, colloidally monodispersed and highly photoluminescent InP based nanoparticles were synthesized by the hot-injection approach under an inert atmosphere. In addition, a protective shell (ZnS, ZnSe) coating methods have been applied to provide optical stability to InP nanoparticles. Moreover, carbon-based nanoparticles with high optical stability and being dispersible in water were synthesized using the bottom-up method. Security codes that cannot be detected in daylight have been created on different subtrates (paper, polymer, glass, etc.) by using screen printing and inkjet printing methods, which are well known printing methods using the synthesized nanoparticles. In addition, the authenticity of the security codes was checked using a commercial fiber optic based spectrometer (Ocean Optics spectrometer) and a handy hand-held optical device called the Quantag sensor developed by Quantag Nanotechnologies. Thus, a verification method that can be distinguished by a simple detection device is proposed. The synthesized nanoparticles were furthermore dispersed in a polymer solution to create random droplet and droplet/fiber patterns by electrospinning method. Thus, unique and inimitable security codes detectable under UV light were created which may be used in the fight against counterfeiting. To check the authenticity of the original security codes created; images collected with a simple smartphone microscope and a database was created in which the original patterns were recorded. The originality of the random patterns obtained was checked by comparing it with the patterns recorded in the database. In addition, the spectral information of the particle from the droplet/fiber pattern obtained was determined with a simple hand-held device (Ocean Optics optical spectrometer). Thus, by reading spectral information from the pattern, the spectral signature of the nanoparticles was determined and thus a second-step security was created. In this way, a two-stage anticounterfeiting technology that is impossible to imitate has been developed. As a conclusion, it is believed that the security codes developed in this study will pave the way for the commercialization of quantum labeling technology.
Development of semiconductor nanocrystals for biotechnological applications
(Izmir Institute of Technology, 2008) Ünlü, Caner; Özçelik, Serdar
Semiconductor nanocrystals are very useful tools in biological applications because of their unique optical properties. In this study, synthesis and characterization of CdTe / CdS and CdSexS1-x nanocrystals were carried out. CdSexS1-x nanocrystals were synthesized by a modified two phase method. Highly luminescent (Quantum yied . %80) , monodisperse and face centered cubic CdSexS1-x nanocrystals were obtained in toluene. The size of nanoparticles varies from 3.5 to 3.7 nm Ligand exchange was performed on CdSexS1-x nanocrystals and luminescent water soluble CdSexS1-x nanocrystals were obtained. CdTe / CdS nanocrystals were synthesized in one step and and one pot by a modified method. Face centered cubic, luminescent (Quantum yield . 30%) and monodisperse CdTe / CdS nanocrystals with different sizes in a size range from 4.7 to 9.3 nm were obtained in water. Toxicity of CdTe / CdS nanocrystals was determined by MTT test. The lethal concentrations were respectively 1.0 and 15 .g/ml for PC3 and MCF7 cells. Confocal microscopy shows that the nanoparticles enter to the cytoplasm of cells.
Development of sub-cellular organelle targeted fluorescent silica nanoparticles
(Izmir Institute of Technology, 2019-12) Yüksel, Almila; Özçelik, Serdar
Silica nanoparticles have been studied extensively in cellular applications due to their physicochemical properties. The surface of silica nanoparticles represent the key parameter in biological studies. Owing to their versatile surface chemistry, have ability to increase bioavailability and selectivity. Therefore, it is significant to understand how biomolecules interact with the surface of silica nanoparticles. The study reviews how synthesized both negative and positive potential silica nanoparticles and can transfer their properties to the cells. In the second part, our synthesized silica nanoparticles were characterized physicochemically using some instrumental devices. To answer the role of silica nanoparticles in the cells, some outcomes such as viability test, image analysis, colocalization analysis and mitochondrial membrane potential were investigated. A549 (adenocarcinomic human alveolar basal epithelial cells) and BEAS-2B (human bronchial epithelial cells) cell lines were selected in our studies. Our results showed the cytotoxicity was dose and time dependent in direct proportion. Mitochondrial accumulation were observed in cells treated with the silica nanoparticles according to Pearson’s Coefficient Correlation and Image J analysis. The study concluded that the silica nanoparticles can be used in the field of targeted delivery and bioimaging in cellular studies.
The effects of engineered silica nanoparticles on the cellular behaviours of human hepatocellular carcinoma cell lines
(Izmir Institute of Technology, 2018-07) 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.
Molecular beam epitaxial growth of ZnSe on (211)B GaAs
(Izmir Institute of Technology, 2017-06) Yavaş, Begüm; Ateş, Serkan; Özçelik, Serdar
The Mercury Cadmium Telluride (Hg1-xCdxTe) play important role for infrared (IR) focal plane array application. It is grown on variety alternative substrates which are Si, Ge, GaAs or GaSb. When GaAs is compared with the others alternative substrate, it is more preferable due to having good surface polarity and also easily commercially available of high quality. When HgCdTe epilayer is grown directly on the GaAs substrate, there exist some dislocations in the epilayer due to large lattice mismatch between HgCdTe and GaAs substrate.The CdTe semiconductor is grown like a buffer layer to reduce dislocation in the HgCdTe epilayer grown on GaAs or other alternative substrate [1].The crystal quality of CdTe buffer layer directly affected HgCdTe epilayer. Therefore, CdTe needed to be low defect density.Because of %14.6 lattice mismatch between CdTe and GaAs [2], some defects are observed in CdTe buffer layer. ZnSe epilayer can be used to decrease lattice mismatch between CdTe and alternative substrate. When ZnSe interlayers are grown with high quality, CdTe affects positively. The aim of this theses is the growth of ZnSe epilayer films on (211) GaAs substrates by molecular beam epitaxy (MBE). The effect of growth temperature, VI/II flux ratio and deoxidation process with In and As were studied in this study. Crystal qualities of films were investigated by using X-ray diffraction. The surface morphology of ZnSe films were analyzed by atomic force microscopy and Nomarski microscopy. Vibrational phonon modes, thermal and elastic strains of ZnSe epilayer were observed by using Raman spectroscopy.
Preparation of electrospun composite fibers based on PS-PI-PS/CdSxSe1-x nanoparticles
(Izmir Institute of Technology, 2011) Aşkın, Görkem; Demir, Mustafa Muammer; Özçelik, Serdar
Polymeric fibrous films were prepared based on polystyrene-b-polyisoprene-bpolystyrene triblock copolymer (SIS) and CdSxSe1-x nanoparticles by electrospinning process. SIS with 14 wt % Styrene (14% PS-SIS) and 22 wt % Styrene (22% PS-SIS) triblock copolymers were employed. Both of them undergo microphase separation. While the former shows cylinder-like morphology, the latter exhibits the lamellae one. CdSxSe1-x partciles were stabilized by two different surfactant molecules: i) n-trioctylphosphine oxide (TOPO) and ii) oleic acid (OA). When the particles were blended with 22% PS-SIS, particles capped with TOPO preferentially filled to PS domain whereas particles capped with OA loaded into the PI domain. Composite electrospun fibers were prepared with a diameter of 1.5 mm on average. Electrospinning parameters (potential difference, solution concentration, flow rate) were investigated on fiber morphology. The films are colorless under day light and have strong green emission under UV light.
Production and characterization of water soluble CdSeTe based core/shell nanocrystals and their applications in bioimaging
(İzmir Institute of Technology, 2009) Özdemir, Seda; Özçelik, Serdar
In recent years, nanotechnology has become one of the most intensively studied fields. At the nanometer scale, materials have unique electrical, optical, magnetic and chemical properties. They can be used for a wide variety of applications such as electrooptical devices, tagging and medical applications. The goal of this study was to produce water-dispersible alloyed CdSexTe1-x semiconductor nanocrystals, which are suitable to interact with biomolecules. CdSexTe1-x nanocrystals were synthesized by a single step aqueous synthesis method. Monodisperse, CdSexTe1-x nanocrystals with zinc blende structure were obtained in water. Synthesized nanocrystals emit in the range from 528 nm to 620 nm. CdSexTe1-x nanocrystals have 17% photoluminescence quantum yield, after the CdS shell coating the photoluminescence quantum yield increased up to 22%. MTT test and Trypan Blue tests were used to evaluate the toxicity of CdSexTe1-x nanocrystals. MTT measurements reveal that the MCF7 cancer cells are not affected by the nanocrystals at any dosage and exposure condition, but lethal effects are determined at the concentration of 1.0ug/ml for the PC3 cells. The BEAS 2B cells are very sensitive to the nanocrystals and do not proliferate at concentration of 0.5ug/ml. Confocal microscopy studies show that the nanocrystals has ability to penetrate to the cytoplasm of cells.
Rendering optical and structural properties of semiconductor nanocrystals by chemical doping
(Izmir Institute of Technology, 2012) Sevim, Seçil; Özçelik, Serdar
Semiconductor nanocrystals are widely used in technologic applications because of their unusual and tunable optical properties. In this study we synthesized two type of semiconductor nanocrystals by the aqueous synthesis method. Colloidal HgCdTe semiconductor nanocrystals were synthesized by cation exchange reaction at room temperature. The absorption and photoluminescence spectra of water dispersible semiconductor nanocrystals appeared in NIR range of the electromagnetic spectrum. Aging process showed higher shift to red region in absorption and fluorescence spectra for HgCdTe nanocrystals. Increasing the initial Hg:Cd mole ratio spectral tuning was achieved. The size of the semiconductor nanocrystals was controlled between 8 nm to 44 nm by selecting the size of initial CdTe nanocrystals. Water dispersible Gd doped CdTe nanocrystals were also studied by changing initial Cd:Gd mole ratio. CdS shell was formed in order to make more compact and stable Gd doped CdTe nanocrystals. Size of Gd doped CdTe/CdS nanocrystals was tuned up to 38 nm by increasing initial Gd content. The optical spectra of Gd doped CdTe nanocrystals were in the range from 535 nm to 555 nm after 4 hours reaction time. Photoluminescence quantum efficiencies of Gd doped CdTe nanocrystals were measured and found out that doping Gd, decrease the quantum yield of nanocrystals. We concluded that CdTe nanocrystals can be used to synthesize doped nanocrystals by chemical doping. We demonstrated that optical and structural properties of Hg and Gd doped CdTe can be rendered by chemical doping.
Snythesis, characterization of borosilicate nanoparticles and investigation of their cytotoxicity and genotoxicity in human cell lines
(Izmir Institute of Technology, 2011) Öztürk İlgü, Ekin; Özçelik, Serdar
In this study, firstly, we aimed to synthesize silica and borosilicate nanoparticles by the Stöber method. We then investigated the biological response of bronchoalveolar carcinoma-derived cells (A549) and healthy bronchoalveolar cells (BEAS2B) against the silica and borosilicate nanoparticles, by evaluating cytotoxicity and genotoxicity. The nanoparticles were synthesized by a modified Stöber method. To prepare borosilicate nanoparticles tri methoxy boroxine (TMB) was used as boron source to coat the surface of the silica nanoparticles. By varying the amounts of ethanol and ammonia the size of nanoparticles were tuned from 60 to 450 nm. We proved the presence of boron in the borosilicate nanoparticles by Energy-Dispersive X-ray (EDX), Fourier Transformed Infrared (FTIR) spectroscopy and an acid-base titration method. Cytotoxicity and genotoxicity induced both silica and borosilicate nanoparticles were investigated for the cell lines of A549 and BEAS-2B. Silica and borosilicate nanoparticles in all three sizes and dosages up to 500 Î¼g/mL did not induce cytotoxic effects in A549 cells with incubation time up to 72 hours. The same amount of particles did not result in any cytotoxicity in BEAS-2B cells for 24 hours incubation, but they showed cytotoxic effects when the incubation time was increased to 48 and 72 hours. Furthermore, nanoparticles with sizes of 60 and 100 nm showed no genotoxicity for A549 but for BEAS-2B cells, silica nanoparticles induced genotoxic effects contrary to borosilicate nanoparticles.
Synthesis and characterization of monodispere silica based functional nanoparticles for multi-purpose applications
(Izmir Institute of Technology, 2009) Altın, Burcu; Özçelik, Serdar
The Stöber method was performed to tune the size of monodisperse silica nanoparticles in the range of 10 to 500 nm. It was observed that increasing amount of reactants favors the formation of larger particles A Stöber method in the presence of L-lysine as a catalyst instead of ammonia was developed to prepare well-ordered, highly monodisperse silica nanoparticles based on the hydrolysis and condensation of TEOS. The effect of medium temperature, amounts of L-lysine, TEOS, octane and dye on the size of particle was investigated. It was found that L-arginine increased the size of particles. The amount of TEOS was determined to be 50.0 mmol to obtain the smallest size of particle. The mole of L-lysine slightly altered the size of particles, however the surface of particles was substantially covered by L-lysine. The presence of octane does not change the size of particles. The amount of dye molecule Rhodamine B isothiocyanate (RBITC) does not alter the size of nanoparticles. We showed that temperature plays important role tuning the particle size from 5.0 nm to 80.0 nm.MTT assay indicates no cytotoxicity of the silica particles against MCF-7 (human breast cancer cell lines) and PC-3 (human prostate cancer cell lines) cancer cell lines. The particles enter to the cells within 5 minutes with a concentration of 0.1.g/mL. We propose that these particles can be used in the field of bioimaging and drug delivery.
Synthesis and control of exciton dynamics in CdTe, CdTe/CdS and ZnxCd1-xTe colloidal nanocrystals
(İzmir Institute of Technology, 2012) Eral Doğan, Leyla; Özçelik, Serdar
The aim of this study is to synthesize cadmium-based semiconductor colloidal nanocrystals and to control their exciton dynamics by tuning the size and composition of the nanocrystals (NCs). CdTe, CdTe/CdS binary, and ZnxCd1-xTe ternary semiconductor NCs are prepared by wet chemistry. The reactions are thoroughly optimized to enhance the optical properties. The optical properties of CdTe and CdTe/CdS are tuned by the size of the NCs by adjusting the reaction (the growth) time. Coating CdTe NCs with CdS layer enhances the photoluminescence quantum yields up to 45%. ZnxCd1-xTe ternary nanoalloys were synthesized by varying the initial mole ratios of metals (Zn/Zn+Cd) and the growth time. The size and the composition-tunable ZnxCd1-xTe nanoalloys exhibit highly luminescent optical properties. When the amount of initial Zn precursor is low, the nanoalloys have Cd-rich and Zn-poor internal crystal structure. However, at higher amount of Zn precursor, the nanoalloys have Zn-rich and Cd-poor core exhibiting gradient composition. The exciton interactions and dynamics are investigated as a function of the size of CdTe/CdS, and the composition and the size of ZnxCd1-xTe nanoalloys. The exciton interaction yields amplification in the output signal at the threshold of 1015 photon/cm2s per laser pulse. The exciton lifetimes are in the range of picoseconds to nanoseconds. The decay associated spectra are affected by the laser power, size and composition of the NCs. As the laser power increases new excitonic states are created especially in ZnxCd1-xTe nanoalloys. Multiexcitons were created in the NCs depending on the laser power. Small NCs exhibit stronger exciton-exciton interactions under high laser power compared to larger NCs. However larger NCs have lesser exciton density, therefore reducing the exciton-exciton interactions.
Synthesis, characterization of CdSxSe1-x quantum dots and evaluation of their real-time motions in live cells
(Izmir Institute of Technology, 2011) Ünal, Gülçin; Özçelik, Serdar
The use of quantum dots as fluorescent labels in bioimaging is the most intensively studied subject. The aim of this study is to elucidate locations of quantum dots and track their motions in real time through confocal microscopy and to evaluate influence of surface chemistry on diffusions of quantum dots in live cells. In this study, trioctylphosphine oxide (TOPO) capped CdSxSe1-x quantum dots were synthesized and then TOPO molecules were exchanged with 3-mercaptopropionic acid and N-acetyl-Lcysteine to make quantum dots water dispersible for cellular imaging. Human lung adenocarcinoma epithelial cells (A549) and human bronchial epithelial cells (BEAS-2B) were incubated 1 hour with CdSxSe1-x quantum dots with a concentration range of 1-10 g/mL. Localizations and real time motions of quantum dots were tracked by a spinning disc confocal microscope. The center of fluorescent spots of quantum dots was determined by 2D Gaussian fitting with a sub-pixel resolution (<100nm/pixel). The mean square displacements, diffusion coefficients and trajectories in which quantum dots made motions were analyzed by the software ImageJ with a plug in Spot Tracker. Confocal images showed that both MPA and NAC cappped quantum dots were observed in the cytoplasm of cells. Trajectories of quantum dots in cellular environment demonstrated that the quantum dots performed various types of motions in live cells. Unimodal, trimodal and multimodal distribution histograms of the diffusion coefficeints were obtained for different capping agents (MPA and NAC) and cell types (A549 and BEAS-2B). We conclude that the surface chemistry regulates the motion of the quantum dots in the cellular environment.
Synthesis, physicochemical characterization, and biosensing applications of gold nanoparticles
(Izmir Institute of Technology, 2018-04) Üçüncü, Melek; Özçelik, Serdar
Cancer is one of the leading diseases that cause death all around the world. In Turkey, lung cancer is the most common type of cancer type in men and it is the fifth in women. Unfortunately, the percentage of treatment of lung cancer is too low. Gold nanoparticles (AuNPs) are widely used in the biotechnology as imaging, diagnosis, and therapeutic agents because of their unique properties such as plasmon resonance, easy synthesize, biocompatibility, and facile surface modification. In this study, it is aimed to design gold nanoparticles as biosensors for lung cancer cells. For this purpose, different sizes (5-40 nm) of Au nanoparticles were synthesized and their uptake and distribution into the lung cancer cells were investigated. The results of the study revealed that cellular uptake of gold nanoparticles are high for the size of 20 and 40 nm. The optimal visibility into the cells was achieved by using DIC microscopy in which the particles uptaken into the cytoplasm and localized at around nucleus of cells. In the second part of the study, surfaces of 20 and 40 nm particles were conjugated with RGD peptides and their distribution and light scattering properties were investigated in living cells by using dark-field microscopy. Due to the receptor-mediated endocytosis, RGD-AuNPs showed different distribution within the cells. These results indicate that the RGD conjugated Au nanoparticles exhibits much higher light scattering properties than non-conjugated nanoparticles. In addition to this, synthesized Au nanoparticles were conjugated with nucleus-localized peptide (NLS) and directed to the nucleus of cancerous (A549, H358) and healthy (BEAS2B) lung cells. The nucleus targeting properties of the NLS conjugated particles were also investigated to understand if there is any cell line selectivity. The internalizations of peptide conjugated Au nanoparticles into cell lines were visualized in living cells by using DIC microscopy. NLS conjugated AuNPs internalized into nucleus of A549 and H358 cancer cells. Although NLS conjugated AuNPs present inside the cytoplasm of BEAS2B cells, they did not localize into the nucleus of normal cell lines.