Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
Browse
3 results
Search Results
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.Doctoral Thesis Development of a Plasmonic Biosensor for Detection of Exosomes(Izmir Institute of Technology, 2020) Taykoz, Damla; Bulmuş Zareie, Esma Volga; Tekin, Hüseyin CumhurThe aim of this work was to develop Localized Surface Plasmon Resonance (LSPR) surfaces for quantitative detection of exosomes from different sources. For this aim, gold nanorods (AuNRs) with a mean diameter of 40 nm with an aspect ratio of 2.9 were first synthesized and characterized. The self-assembly of AuNRs on glass wafers were optimized through several experiments. In parallel, PEGylation of cetrimonium bromide (CTAB) stabilized AuNRs was investigated using PEGs with three different molecular weights via LSPR, zeta potential and XPS techniques. PEGylated AuNRs were further self-assembled on silanized microscope slides as confirmed. Surface functionalization of AuNR patterned slides was performed using alkane thiol molecules having carboxylic acid and hydroxyl functional groups and confirmed via XPS, FTIR and zeta potential. Specific antibodies (Ab) were conjugated to the surface following two different methods, i.e. click and NHS/EDC chemistry. To perform click chemistry strategy, ImmuneLink® molecules were conjugated with Abs and the final conjugate was used to functionalize surfaces prepared beforehand using azide bearing molecules. The functionalization procedure was confirmed via XPS FTIR and LSPR spectroscopy. The orientation of the antibodies on the AuNRs patterned surfaces was investigated with LSPR in comparison with conventional EDC/NHS chemistry. The click-chemistry strategy proved to provide conjugation of antibodies through their Fc regions exposing Fab regions better for antigen recognition. Finally, surfaces functionalized with a variety of antibodies were used to detect first a pregnancy-associated protein, PLAP, and then exosomes obtained from human semen samples with pre-determined exosome concentrations. The LoD of the biosensor surfaces was found to be between 103-104 exosomes/mL and 5 ng/mL (0.3 pM) PLAP. Human breast cancer cell culture samples having an unknown concentration of exosomes were further analyzed using the newly developed LSPR biochips and the exosome concentration was determined as 108 exosomes/mL for MCF-7 cell line and 107 exosomes/mL for MDA-MB-231 cell line.