Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Synthesis, Characterization and Sensor Studies of Thiophene Conjugated Copolymers(01. Izmir Institute of Technology, 2024) Kurt, Tolunay; Yıldız, Ümit HakanBu tez, biyosensör ve biyogörüntüleme uygulamaları için katyonik ve iyonik olmayan monomerlerin ve bunlara karşılık gelen polimerlerin sentezini, karakterizasyonunu içerir. Katyonik polimerler oksidatif polimerizasyon yoluyla sentezlendi ve yapısal ve optik özellikleri NMR, Kütle Spektroskopisi, Absorbans Spektroskopisi, Floresan Spektroskopisi, Raman Spektroskopisi, Dinamik Işık Saçılması, Zeta Potansiyel Yük Analizi ve Kuantum Verim Analizi kullanılarak kapsamlı bir şekilde karakterize edildi. 3-bütoksi-4-metiltiyofen (M1) ve N-alil-N-metil-N-(3-((4-metiltiyofen-3-il)oksi)propil)prop-2-en-1-aminyum (M2) monomerlerinin değişen oranlarıyla üretilen homopolimerler ve kopolimerler, çeşitli uygulamalardaki performansları açısından analiz edildi. Tezin önemli bir odağı, özellikle nanometre aralığında (5-30 nm) polimer noktalarının (Pdots) yapılarını optimize ederek, bu nanomalzemelerin kan-beyin bariyeri (BBB) boyunca geçirgenliğini potansiyel terapötik kullanımlar için artırmaya yerleştirildi. Sentezlenen polimerler arasında P4 (1:1 oranında M1/M2), BBB'yi geçmede üstün performans gösterdi. Ek olarak, tez, özellikle ağız sağlığı bağlamında, Candida türlerinin tespiti için optik problar olarak katyonik polimerlerin uygulanmasını araştırmaktadır. Polimerler, Candida bağlanması için gelişmiş floresans ve yüksek özgüllük göstererek, Oral Kandidiyazis'in invaziv olmayan tespiti için büyük bir potansiyel göstermektedir. Bulgular, bu katyonik polimerlerin Oral Candida'nın erken tespiti için etkili tanı araçları olarak hizmet edebileceğini ve klinik yönetim için önemli bir vaat sunabileceğini göstermektedir. Bu tez, katyonik polimerleri ve Pdot'ları hem oral mantar enfeksiyonlarını tespit etmek hem de özellikle kan-beyin bariyeri boyunca ilaç iletimini iyileştirmek için potansiyel biyomedikal uygulamalar için oldukça etkili malzemeler olarak sunmaktadır.Master Thesis Synthesis and Characterization of Polycaprolactone-Polyvalerolactone Copolymer and Its Use in Melt Electrowriting Applications(01. Izmir Institute of Technology, 2024) Dinçkal, Sanem; Yıldız, Ümit HakanThis thesis focuses on the synthesis and characterization of Poly(ε-caprolactone) (PCL) and its block copolymers, Poly(ε-caprolactone)-b-Poly(4-hydroxyvalerate) (PCL-b-P4HV) and Poly(ε-caprolactone)-b-Poly(δ-valerolactone) (PCL-b-PVL). These polymers were synthesized through ring-opening polymerization of various lactones (ε-caprolactone, γ-valerolactone, and δ-valerolactone) using biocatalysts such as citric acid, glycolic acid, salicylic acid, boric acid and acetic acid. Detailed analytical and thermoanalytical characterizations were performed. Differential Scanning Calorimetry (DSC) showed that most homopolymers and copolymers exhibited crystallization (Tc) and melting temperatures (Tm) varying between 5-25°C and 50-65°C respectively, confirming successful polymerization. DSC thermograms of block copolymers revealed that solvent choice for precipitation affected crystallinity and thermal properties, with a small second melting point observed due to different crystalline forms. Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) confirmed the homopolymerization of Poly(ε-caprolactone) using citric, glycolic, and salicylic acids. Mass spectrometry further revealed characteristic peaks corresponding to expected molecular weights and compositions of the copolymers. The presence of these peaks corroborated the formation of block copolymers with distinct blocks of PCL, P4HV, and PVL confirmed the molecular integrity of the synthesized block copolymers. This thesis provides a comprehensive analysis of the synthesis and characterization of block copolymers, offering insights into their structural properties and potential applications. The findings contribute to the understanding of the polymerization process and the properties of the resulting materials, which are significant for industrial and biomedical applications. The resultant copolymers were utilized in Melt Electrowriting process to provide tissue scaffold. Despite their brittleness, all copolymers were electrowritten without issues, indicating their potential interest in tissue engineering applications.Master Thesis Investigation of Ion Transport Properties of Organic Electrochemical Transistors(01. Izmir Institute of Technology, 2022) Küçüktartar, Tuğçe; Yıldız, Ümit HakanOrganic electrochemical transistors (OECTs) comprise large amplification in current response while operating at low voltages and have high transconductance due to its volumetric capacitance created by ion injection from electrolyte through the whole organic semiconductor channel. OECTs are switchable by doping and de-doping of active channel via application of positive or negative gate bias. One of the most common organic material for OECTs is the conductive polymer, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). PEDOT:PSS offers prominent advances because of their coupled electronic and ionic conductance, morphology and optical properties. Although the complex working principle of OECT has been tried to be elaborated with several models in literature, the conduction of ions and electrons in the channel has not been fully elucidated. In this thesis, the transformations between un-doped, doped and de-doped state investigated systematically based on the electrical (OECT), structural and morphological characterization of PEDOT:PSS thin film. Measurements were conducted with different dopant molecules and the repeatability of the device was investigated. As a result, the most stable drain and gate voltage range in which the device works has been determined. In addition, the X-ray photoelectron spectroscopy (XPS) investigation performed which is revealed that the density of the bipolaron formation of PEDOT:PSS in the doped state increase as compared to its natural form in the de-doped state. XPS mapping on OECT devices suggested that ions migration is homogeneously generated by applied bias.Master Thesis First-Principles Investigation of Novel Single-Layers and Heterostructures of Group Iii-Iv Elements(01. Izmir Institute of Technology, 2022) Yayak, Yankı Öncü; Yıldız, Ümit HakanSince the discovery of graphene, two-dimensional materials have been the focus of interest in various branches in scientific community. Wide range of ultra-thin materials have been investigated both theoretically and experimentally such as metal chalcogenides, Xenes and h-BN. In addition to this, two-dimensional (2D) van der Waals heterojunctions have become one of the central research topics due to their wide range of possibilities. Since 2D van der Waals heterostructures are combinations of two or more ultra-thin materials with different properties, creating a heterostructure with desired optical, electrical and/or mechanical property is theoretically probable. Motivated by these, this thesis focus on the investigation of structural, vibrational and electronic properties of 2D materials and their heterostructures by means of density functional theory-based first-principle calculations. In chapter 3, single-layer Ge3N4 is shown to be both electronically and dynamically stable. Also, simulated Raman spectrum of single-layer Ge3N4 have characteristic vibrational properties. Another property of single-layer Ge3N4 is that it is a indirect band gap semiconductor and this property is uneffected by external strain. And lastly, the value of band gap varies with the applied external strain. In chapter 4, a dynamically stable single layer structure of AlAs is proposed and four possible stackings of AlAs/InSe heterobilayer were investigated. Electronic band dispersions revealed that all four stackings are direct band gap semiconductors and have type-II alignment. Moreover, simumlated raman spectra revelaed that identification of the 1T and 2H phase can be done with Raman spectroscopy. The band gap can be tuned based on the direction and magnitude of the electric field. Direct to indirect band gap transition as well as heterojunction type changes from type II to type I occurs under negative electric field.Master Thesis Investigation of Microbial Biofilm Formation Using Electrochemical Impedance Spectroscopy and Equivalent Circuit Modelling(01. Izmir Institute of Technology, 2021) Kuş, Anılcan; Yıldız, Ümit HakanBacterial biofilm is like a cooperative form of planktonic bacteria that colonize to acquire more nutritious and become resistant to surroundings. The communal organization results from the connection of bacteria by polysaccharides, lipids, or the extracellular matrix, which can provide a protective environment for living cells and communicate between them or allow specific types of chemicals inside through the matrix. 60%-80% of the infections are known to be biofilm-related. Bacterial biofilms are more resistant to antibiotics, and treating them with the wrong antibiotics might result in a thicker biofilm. In order to overcome these difficulties and researching new treatments for biofilm inflammation understanding the formation process is essential. For this manner, Electrochemical Impedance Spectroscopy (EIS) has potential uses in various fields such as biosensors, corrosion studies, healthcare owing to its facile operation and affordable devices to conduct electroanalysis. EIS calculates the excitation voltage and current generated with the oscillating frequency. Developing impedimetric methods are gaining attention due to the operation being label-free. Considering its label-free nature, EIS is a possible candidate to explain the electrodynamics of living systems such as cell-matrix interaction, biofilm formation in vitro. Detection of those is essential to prevent infections and to develop medical needs to cure them. The thesis focuses on understanding the electrodynamics of bacterial biofilm formation via electrochemical methods such as square wave voltammetry (SWV), Open Circuit Potential (OCP), and EIS. After carrying out the experiments, time-dependent circuit models for EIS were built, and the data were extracted to demonstrate changes in the bacterial system.Master Thesis Design and Development of Paper-Based Microfluidics for Point-Of Applications(01. Izmir Institute of Technology, 2020) Özefe, Fatih; Arslan Yıldız, Ahu; Yıldız, Ümit HakanPaper-based microfluidics is a subarea of microfluidics which is recently used in various applications from diagnostics to environmental monitoring, and to food safety. In such microfluidic systems, a test platform is formed from a paper substrate instead of silicon and polymers, such as poly-dimethylsiloxane, poly-methyl methacrylate, and etc. The main goal of this thesis is the development and fabrication of a paper-based microfluidic device (μPAD), which could be used in point-of-care (POC) applications. The characterizations of μPADs, which were fabricated via laser ablation methodology, were performed in terms of their surface and barrier characteristics, and liquid sample flows within μPADs. Depending on the characterization, nine different fabrication parameters, 10P40S (10%Power & 40%Speed), 10P60S, 20P90S, 30P50S, 30P100S, 40P80S, 40P100S, 70P80S, and 70P100S, were identified as optimized fabrication parameters. Also, two designed models of μPADs, 1S4T-Type2 and 1S4T-Type3, were selected to be used in the detection of BSA and recombinant Hepatitis C Virus (HCV) protein. The BSA and HCV (1 mg/ml) in PBS solution were successfully detected via naked eye depending on the colorimetric sensing through micro-paper enzyme linked immunosorbent assay (μP-ELISA) protocol. Moreover, the limit of detection (LoD) values for HCV were determined in 1S4T-Type2 μPAD as 1.000, 0.883, and 0.796 ng/ml when the detection was performed via naked eye, smart-phone, and bright-field microscope, respectively. Also, the easily-disposable 1S4T-Type2 μPAD provided 14 times faster and 45 times cheaper detection of HCV compared to conventional ELISA techniques. Consequently, the developed 1S4T-Type2 μPAD presented low-cost, easy-to-use, and rapid detection of HCV as POC devices.Master Thesis Synthesis of Polythiophene-Polyurethane Soft Nanoparticles for Bioimaging Applications(Izmir Institute of Technology, 2020) Karabacak, Soner; Yıldız, Ümit HakanIn this study, synthesis of fluorescent polythiophene and polyurethane soft nanoparticles carrying them was carried out for bioimaging applications. Conjugated polythiophenes and polyurethane derivatives were obtained by changing their structural properties such as size, charge, and group, and were characterized by nuclear magnetic resonance, infrared spectroscopy, dynamic functional light scattering, fluorescent microscopy, methods. In the study, changing characteristics of polyurethane nanoparticle materials were investigated depending on the synthesis conditions. Synthesis of polyurethane nanoparticles was carried out by miniemulsion polymerization technique and synthesized as nanosphere to be more controllable on nanoparticle size, morphology and stability. The sizes of the polyurethane nanospheres varied in the range from 10 to 500 nm. Polyelectrolyte-polyelectrolyte complexation was investigated using cationic polythiophene-anionic polythiophene for use in bioimaging applications. Synthesized conjugated polythiophenes are divided into two groups as anionic and cationic polythiophenes. In this thesis, three kinds of cationic polythiophene synthesis are included, but poly (1,4-dimethyl-1- (3- ((4-methylthiophene-3-yl) oxy) propyl) piperazine-1-ium bromide) (PT4) was used as cationic conjugated polythiophene in the studies. Anionic polythiophene acetic acid (PTAA) was used as a counter-charged polythiophene. In addition to these studies, dual-mode imaging agents were prepared, consisting of PTAA as fluorescent agent and gadolinium metals as magnetic agent. The bioimaging studies continued under conditions imitating biological systems, and the potential of the proposed bioimaging agents was investigated.Master Thesis Modification of Gold Surface by Layer-By Reactive Coating of Polyester-Polyethyleneimine Based Gel(Izmir Institute of Technology, 2020) Yıldırımkaraman, Öykü; Yıldız, Ümit HakanPolymeric gels defined as soft and solid-like systems that enable to retain a large volume of solvent and their high molecular weight provides long-term stability without crystallization. Therefore, the use of polymeric gels in the fields of energy and sensor technologies has become advantageous. In this thesis, the polymeric gel is successfully synthesized on the gold surface by Aza-Michael addition reaction of the polyester scaffold with a triple covalent bond and branched polyethyleneimine which is a secondary amine source. The polyester-polyethyleneimine based gel was generated on the isocyanate functionalized gold surface by using the grafting-to methodology. The morphology of the surface and thickness of the coating can be adjusted by layer-by-layer reactive coating on the gold surface of polymer structures. Electroactive properties are acquired for different application areas of the synthesized gels. To provide modular electron transfer, polyethyleneimine was modified with ferrocene carboxaldehyde prior to obtaining gel on the surface. The gel interface on the gold surface will increase the surface area and activity due to its three-dimensional structure and adjustable morphology. The number of the immobilized structures, the electroactive species in a unit area and electron transfer increases. The modified electrode surfaces coating yields and electroactivity examined with electrochemical methods, Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. The morphological properties investigated by Atomic Force Microscopy. Additionally, polyester-based gels lithium-ion conductivity was investigated. Dissociation of lithium perchlorate in the gel and enhancing the conductivity was investigated. Indium tin oxide coated glasses were used as an electrode to characterize lithium ion conductivity.Master Thesis Fabrication of Polymer Nanofiber / Poly (3,4 Ethylene Dioxythiophene) / Metal Particle Hybrid Composite for Volatile Organic Compound Sensing Applications(Izmir Institute of Technology, 2020) Acar, İrem; Yıldız, Ümit HakanThis study aims to produce polymer nanofiber / poly (3, 4 ethylene dioxythiophene) / metal particle hybrid composite as a bioelectronic interface for the detection of volatile organic compounds in human breath. The sensor platform consists of two layers: polymeric nanofiber structure and conductive layer. Polyurethane (PU), polycaprolactone (PCL) and poly L-lactide-co-?-caprolactone (PLLCL) were selected to form polymeric nanofibers with electrospinning. For electrospinning process, solutions of polyurethane (PU) (25wt%) in DMF, polycaprolactone (PCL) (20wt%) in DCM (4) -DMF (1) and poly L-lactide-co-?-caprolactone (PLLCL) (10wt%) in DCM (9) -DMF (1) are prepared. PU, PCL and PLLCL polymer solutions are subjected to 25 kV, 29kV and 25 kV electrical potential, respectively, to produce electrospinning fibers. Poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-walled carbon nanotubes (MWCNTs) are used to produce conductive layers on PU, PCL and PLLCL polymer nanofibers. The produced sensor platforms are tested by the electrochemical station, which records the electrical current change over time. The sensing mechanism is assumed to be the adsorption of VOCs to the conductive PEDOT and CNT layer, thus blocking the electron current on the PEDOT and CNT network and causing resistance change. More clearly; swelling of the polymer structure in the sensor causes destruction in the upper layer and micro-dimensional cracks in the PEDOT and CNT network, increasing resistance to electron flow and decreasing current. Organic volatile compounds (acetone, toluene, ethanol, isopene etc.) are detected from ppm to ppb range and reproducible and reliable responses are recorded.Master Thesis A Novel Approach for Fabrication of Free-Standing Conductive Network: Pedot: Pss Based Bendable Chemo and Photoresistor(Izmir Institute of Technology, 2019) Mutlu, Mustafa Umut; Yıldız, Ümit Hakan; Demir, Mustafa MuammerElectrospinning is a simple and versatile technique for the fabrication of polymeric nanofibrous substrate with high surface to volume ratio. Besides high surface to volume ratio, their dimensional stability and flexibility make it a perfect candidate for conductive network for various sensor applications. Free-Standing conductive network can be fabricated by deposition of PEDOT:PSS or MWCNT through bendable nanofibrous substrate. As a simple example for sensor applications, the moving object has been sensed through the electrostatic interactions between fibers and object. The sensing range has been found to be 1-5 cm above the surface of fabric. By the controlled combination of conductive polymers and electrospun polymer nanofibers effective device miniaturization has been provided without loss of performance. The noncontact motion sensor platform has unique flexibility and light weight holding a potential for wearable sensor technology. For another application as a wearable electronics, the controlled combination of conductive network and light-matter interaction provides opportunities to fabricate photo-resistor exhibits broad band response 400 to 1600 nm that holding promises for ultra-thin sensors used in telecommunication. As a final example, we report the effect of gold and iron oxide nanoparticles on the selectivity and sensitivity of MWCNT or PEDOT:PSS based chemiresistor responsive to VOCs. The interplay between conductive layer by gold and iron oxide nanoparticles resulted a significant conductivity improvement that affecting selectivity which is governed by the interaction between electron-donating VOCs and NP doped conductive layer due to variation in charge carrier densities in conductive layer lattice.