Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Chemical Vapor Deposited Reusable Fluorescent Thin Film Sensor Nanoprobes for the Detection of Heavy Metal Ions(01. Izmir Institute of Technology, 2023) Karabıyık, Merve; Ebil, ÖzgençHeavy metal pollution has made a serious threat to the environment and human health day by day due to developing science, technology and industrial activities, therefore, the importance of selective detection of heavy metals has increased. Heavy metals gradually accumulate in the human body, especially via water sources. Among heavy metals, cadmium is one of the most carcinogenic ones and has harmful effects even in trace amounts. Despite it, detection studies of cadmium ion are very few. This thesis study focuses on the development of Initiated Chemical Vapor Deposition (iCVD) synthesized polymer thin film based quantum dot-nitroxide radical fluorescence sensor nanoprobe, which has a multi-use property and high durability, unlike sensor probes developed for single use in liquid media, and selective detection of Cd2+ ions in real water sources. By examining the effects of pH, concentration, solvent type and reaction time, the most suitable conditions to improve the interaction between Cd2+ ion and the newly developed sensor nanoprobe were investigated. The results proved that it is possible to detect the target ion easily even in complex environments where other heavy metal ions are present. Cd2+ ion detection limit with this proposed nanoprobe was found as 0.195 μM and high recovery percentage (>90%) obtained in standard addition method. In the multi-use study, it was confirmed that nanoprobe could be used repeatedly for the selective and sensitive detection of Cd2+ ion without being influenced by the content of daily water samples. This thesis is a great guide for new fluorescent sensor applications.Doctoral Thesis Two Dimensional Material Based Field Effect Transistor for Biosensing Applications(01. Izmir Institute of Technology, 2023) İnanç, Dilce; Yıldız, Ümit Hakan; Çelebi, CemThis thesis presents research on the use of two-dimensional material graphene as an area-effective transistor and its application in biological fields. The formation of wrinkled and flat structures on the surface of a single-layer graphene area-effective transistor, epitaxially grown for determining the bio-membrane dynamics of graphene, was examined using two different methods of deposition (thermal evaporation and pulsed electron accumulation) of a silicon dioxide (SiO2) layer. The investigation aimed to evaluate the pH and lipid bilayer formation performance of both wrinkled and flat GFETs. Increased sensitivity was determined through electrical measurements, as the oxide layer becomes thinner due to the existence of wrinkles, thus providing electrostatic coating on graphene. A sensor platform of chemiresistor type was developed for the differential determination of volatile organic compounds (VOCs) by synthesizing single-layer, bilayer, and multilayer graphene, enabling the analysis of ethanol (EtOH) and methanol (MetOH). Sensors produced using three different graphene morphologies demonstrated differential MeOH-EtOH responses attributed to the differential intercalation phenomenon in multilayer graphene morphologies when compared to ethanol. For the detection of VOCs such as acetone, ethanol, and hexane in human breath, a polymer nanofiber/multi-walled carbon nanotube or poly (3,4-ethylenedioxythiophene)/gold (Au) and iron oxide (Fe) hybrid bioelectronic interface was developed. Sensitivity studies were conducted by applying pure VOCs at different concentrations to the sensor platforms, and the behavior of the sensor platforms against interfering elements was evaluated by recharacterizing them under CO2 and humidity conditions. Considering the responses of MWCNT-PLLCL-Fe-based sensors to acetone, ethanol, and hexane, the tendency of water molecules to adhere to the Fe surface was shown to decrease water condensation on the conductive layer compared to other sensor configurations, indicating that the humidity effect was minimized in MWCNT-PLLCL-Fe-based sensors.Doctoral Thesis Development of Conducting Polymer-Based Fluorescence On/Off Biosensor for Biomolecule Analysis(01. Izmir Institute of Technology, 2022) Arslantaş, Duygu; Arslan Yıldız, AhuSensitive and selective detection of biomolecules and cells is essential for early diagnosis of diseases, prognosis monitoring, and effective therapy. This thesis aimed to develop a novel fluorescence ‘‘turn-on/off’’ biosensor for biomolecules and cells detection. In this study, cationic polythiophene derivative poly(1,4-dimethyl-1-(3-((4- methylthiophen-3-yl)oxy)propyl)piperazin-1-ium bromide) (PT–Pip) was used as an efficient fluorescence transduction element to discriminate proteins, mammalian cells, and amino acids for the first time. Initially, pH–dependent spectroscopic characterization of the PT–Pip was performed to monitor the conformational and optical changes. The pH sensitivity of the PT–Pip was demonstrated for the first time. Afterwards, the fluorescence ‘‘turn–off’’ phenomena were investigated in detail using citrate–capped gold nanoparticles as an efficient fluorescence quencher. Further, the interaction of target analytes such as proteins, mammalian cells, and amino acids with pre–quenched non–covalent PT–Pip–AuNP complexes was examined. Disruption of the binding equilibrium between PT–Pip and AuNP by analytes resulted in the selective displacement of PT–Pip, which generated signal output as a fluorescence ‘‘turn–on’’ mode. Consequently, for the sensitive detection of biomolecules and cells, chemical tongue sensor arrays were developed utilizing differential sensing approaches. PCA was used for the statistical evaluation of the multi–dimentional fluorescence response patterns. As a result, unique fingerprints were rapidly obtained by the direct sensing of proteins, ratiometric sensing of mammalian cells, and indirect sensing of amino acids. The combination of a differential sensing strategy with an appropriate multivariate statistical technique enabled the selective and sensitive detection and identification of proteins, mammalian cells, and amino acids.