LEE- Nano Bilim ve Nano Mühendislik-Doktora
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ÖgeDevelopment of mıcrofluıdıc based sıngle cell capturıng systems for early detectıon of dıseases(Fen Bilimleri Enstitüsü, 2020)It is known that cancer cells in the bloodstream are quite low compared to other cells in the blood. Microfluidic based systems have been studied for diagnosis, follow-up of the disease and new drug tests to be performed on this disease. A microfluidic based system with two successive regions for separation and analysis has been developed. In the first region, the target cell type is differentiated from a complex mixture containing multiple cells by dielectrophoresis, which allows an insulating particle to be polarized under an electric field. Since different cell types can be polarized at different rates under the same electric field, this method allows the separation of the cells from each other under suitable conditions. In this study, a microfluidic system consists of two consecutive regions, namely the separation and analysis regions are demonstrated. In the first region, the target cell type is separated by dielectrophoresis from a complex cell mixture. The target cells collected in the first region are continuously transferred to the second region and are captured in a single cell array formation at the hydrodynamic capture stations placed on the measuring electrodes. Impedance analysis was performed to establish a platform for detection and drug screening. While both regions were integrated on a single chip in the final device, each region were examined separately during our study. The results of impedance analysis obtained from different cells based on different medium conductivities with a frequency range of 0.1kHz – 500kHz are presented here. We recorded impedance measurements at stations where cells were individually captured before and after cell entrapment. Experimental results are divided into cases where the conductivity of the medium is higher and lower than the cell conductance. Overall magnitude of impedance shift is significantly higher when the medium conductivity is lower than the cell conductance. When all results are evaluated, it can be seen that depending on the target cell type, an optimum medium conductivity and frequency range can be selected so as to obtain the measurement result with the highest sensitivity. A microfluidic cell culture platform, named as organ-on-a-chip in the literature, has been increasingly studied over the last few years to mimic tissue and organ-level physiology, containing a membrane with a continuous and porous structure inhabited by living cells, and with microfluidic channels to mimic the mechanical effects and to supply the necessary nutrients. These platforms create tissue and organ environments that are not possible with traditional 2D or 3D culture systems, and enable real time imaging and analysis of biochemical, genetic and metabolic activities of living cells. In this project, present fabrication techniques of microfluidic devices are used for the fabrication of organ-on-a-chip platforms. The tissue structure was imitated by coating a single-layer cell on the upper and lower sides of the membrane in the structures of the renal chip tubules and lung alveoli on organ-on-a-chip platforms. The cell viability was characterized by MTT test and the cell viability was maintained by providing oxygen, carbon dioxide and nutrient exchange under incubation conditions by means of nutrient medium flow provided into the upper and lower channels, and the barrier property of the cell tissue was measured by electrical resistance (TEER) measurements. The viability of the renal tubules cultured in the microfluidic system between 0-48 hours was recorded by MTT assay. TEER results showed that the tight-junctions of cell tissue were different under static and dynamic conditions in the kidney-on-chip systems. The results obtained by MTT test to measure cell viability were in agreement with TEER and the viability of kidney cells was higher in 48 hours under dynamic conditions compared to static conditions. With the successful culturing of two different cell types under static conditions in lung-on-chip systems, their viability and cell barrier resistance values were recorded by TEER measurement for 0-48 hours. The results obtained by MTT test and TEER measurements showed that lung cells under shear stress and mechanical stress had higher viability than cells under static conditions.
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ÖgeFabrication of nanostructured metal oxide materials and their use in energy and environmental applications( 2020)Metal oxides are considered to be the most vital material class and they show unique chemical, physical and electronic properties when produced on the nanometer scale. In this context, metal oxide nanomaterials are of increasing importance in many industries and are used in applications such as sensors, medical technologies, energy, water treatment, and personal care products. In this thesis, the fabrication of nanostructured metal oxide materials and their use in energy and environmental applications which have strategic and vital importance are focused. The optimization of process parameters for the production of metal oxide nanostructures via industrial-scale production methods and application-oriented modifications of the properties of metal oxides via controlling their size and composition have been realized. Solar energy is an environmentally friendly technology that allows direct energy production from the sun. Perovskite solar cells (PSCs) have been studied intensively in the last decade and they constitute the energy leg of this thesis. In this context, the effects of metal oxide nanomaterials on perovskite cells performance were investigated. The performance of planar and mesostructured PSCs was compared, while all the experimental studies for the production of highly-efficient PSCs were given in detail. The mesoporous architecture allows the deposition of denser perovskite films than planar architecture due to the high porosity. Though higher efficiency was expected due to effective absorption of incoming light, XRD results showed that PbI2 - perovskite conversion in the mesoporous structure was more difficult. The average efficiency of the cells produced with mesoporous architecture was 15.07 %, which was just 0.9 % higher than the planar one. As can be deduced from the absorbance curves and IPCE analysis, this is because of the mesoporous structure showing more absorbance in the 400-600 nm wavelength range resulting in more photocurrent. However, due to the small difference in efficiency and fewer steps in the planar architecture, it was found more viable for industrial scale-up. Air pollution is one of the most critical environmental problems today, and filtration is one of the practical solutions to remove the pollutants, especially particulate matter within the air. However, exhaust gases might be at high temperatures and require high-temperature resistant filter materials. The use of ceramic-based, fibrous filter elements in filtration applications will enable the production of highly efficient filters with high-temperature stability. In this context, SiO2 nanofibrous mats were produced from sol-gel based solutions via centrifugal spinning (CS) and solution blowing (SB) methods. According to results, centrifugally spun SiO2 fibers were found more flexible where fibers have diameters between 1 and 1.5 microns. Solution blown silica fibrous mats consisted of thinner fibers but have denser bead and droplet defects. Besides, due to the fibrous mats obtained by SB had a dense-packed structure it showed more shrinkage during heat treatment. XRD results show that all fibers have an amorphous SiO2 structure after heat treatment at 600°C. According to the porosity analysis, the solution blown and centrifugally spun SiO2 samples had the lowest pore diameters of 5.2 and 10.5 microns, respectively. Moreover, the effects of SiO2 precursor solution concentration on spinnability in the CS method, the diameter of SiO2 fibers, and filtration efficiency were investigated. Contrary to expectations, the average diameter of the fibers has been found to decrease with increasing precursor concentration a result of reduced viscosity of the spinning solution. While all the produced fibers are incredibly flexible, the highest filtration efficiency (43.35 Pa pressure drop and 75% particle capture efficiency) was obtained from the sample that produced from 15 wt.% TEOS added solution. Due to excellent thermal stability and high mechanical performance of centrifugally spun SiO2 fibrous mats they have the potential as filter materials for hot air filtration applications. Photocatalyst-based purification techniques emerge as a solution for recovery of used water. While the studies focused on the development of photocatalyst material with visible light activity, there is also a need for the development of photocatalyst geometries that can be easily separated from treated water. Although nanoparticulate morphology offers high surface area, it is difficult to remove them from treated water. On the other hand, TiO2 is one of the most studied materials among the photocatalysts due to its high photocatalytic activity, photostability, chemical inertness, and low-cost. TiO2 fibers were fabricated via CS and subsequent calcination methods. The effects of precursor concentrations on fiber diameter, surface area, and photocatalytic activity were investigated. Results showed that the fiber diameter was increased from 0.65 to 1.2 µm with increasing precursor content. The calcined fibers consisted mainly of anatase and also a minor amount of rutile phases. PVP used as the carrier polymer for precursor solution also behaved as a nitrogen source for TiO2 fibers during calcination. The slight shift of peaks in XRD, the presence of nitrogen in XPS spectrum and EDX mapping, and the enhanced visible-light photocatalytic response were pieces of evidence for in-situ N-doped TiO2 NFs. Besides, nanoparticles (P25 NPs) were added into the spinning solution to increase the surface area by producing nanoparticle in nanofiber structure, and it was also used as a reference sample. According to the results of photocatalysis tests, the surface area is the dominant factor for photocatalysis under UV illumination and the optical bandgap is the critical factor for the tests performed under visible light illumination. Moreover, recycle analysis showed that fibrous photocatalysts were easily separated from the treated water. In this regard, the fibrous TiO2 was emphasized as the best visible-light photocatalyst, losing only 14% of its degradation performance after the 3rd use. The effect of Al and Li doping on the crystallinity, fiber diameter, optical bandgap, and photocatalytic activity of TiO2 fibers was investigated in the last part of this thesis. Al and Li doped N-TiO2 fibers were successfully produced via CS method and followed calcination. N- TiO2 showed a fiber diameter of 0.54 µm while Al- and Li-doped N- TiO2 had a diameter of 0.94 and 1.15 nm, respectively. While the crystal structure of N-TiO2 transformed from major anatase and minor rutile phases to the only anatase in the case of Al- and major rutile and minor anatase phases in the case of Li-doped N-TiO2. Additionally, band gap values were calculated as 3.00, 2.94, and 3.14 eV for N- TiO2, Li- and Al-doped N- TiO2, respectively. For the photocatalysis tests conducted under UV-light, the most efficient sample was the nanoparticulate TiO2 due to its high surface areas, while all-fibrous structures showed similar activities, which were nearly two times higher than the activity of nanoparticulate TiO2 under visible-light.