Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

Browse

Filters

2021 - 20243

Settings

Author: search.filters.author.Yıldız, Ümit HakanDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Chemistry

Search Results

Now showing 1 - 3 of 3
  • Doctoral Thesis
    Fabrication of carbonnanomaterial-polymer composite microelectrodes for electrochemical sensors
    (01. Izmir Institute of Technology, 2024) Önder, Ahmet; Yıldız, Ümit Hakan
    Düşük hacimli numunelerde iyonların tespiti, küçük boyutları, yüksek hareketlilikleri ve hızlı difüzyonları nedeniyle önemli zorluklar sunar. Potansiyometrik iyon seçici elektrotlar (ISE'ler), maliyet etkinlikleri, kullanım kolaylıkları ve minyatürleştirme potansiyelleri nedeniyle iyon tespiti için güvenilir bir yöntem olarak ortaya çıkmıştır ve bu da onları mikroakışkan uygulamalar için uygun hale getirmiştir. Tezin ilk bölümünde, katı kontak malzemeleri olarak kimyasal buhar biriktirme yoluyla doğrudan cam elyafı (GF) üzerinde büyütülen radyal olarak hizalanmış karbon nanotüpler (RACNT) kullanılarak mikroelektrotların (r-ISE) üretimi açıklanmaktadır. Bir arayüz malzemesi olarak RACNT-GF ile üretilen r-ISE, 7.5×10⁻⁶ M'lik bir tayin limiti (LOD) ve 1.0×10⁻⁵ ila 1.0×10⁻¹ M arasında doğrusal bir yanıt sergilemiştir. RACNT-GF kullanımı, grafit gibi geleneksel katı kontak malzemelere kıyasla LOD'yi ve seçiciliği önemli ölçüde iyileştirmiştir. RACNT-GF'nin yüksek yüzey alanı ve mekanik dayanıklılığı, elektrotun performansını artırmış ve sınırlı mikroakışkan ortamlarda bile kararlı ve tekrarlanabilir potansiyometrik tepkiler sağlamıştır. Tezin ikinci bölümünde, nitrat iyonları için sentetik bir iyonofor olarak moleküler kafese sistematik bir yaklaşım araştırılmaktadır. Kafes moleküllerinin moleküler yapısını ve dolayısıyla boyutlarını değiştirerek, konak-kafes molekülleri ile misafir-NO3- iyonları arasındaki etkileşimi ayarlamayı amaçlamıştır. Altı sentetik moleküler kafes iyonoforu, nitrat seçici bağlanma yetenekleri açısından değerlendirilmiştir. Optimize edilmiş KAFES iyonoforuna dayalı ISE, yüksek bir belirleme katsayısı (R² = 0.9971), -53.1 ± 1.4 mV/on kat ve nitrat tespiti için 7.5×10⁻⁶ M LOD ile 1.0×10⁻⁵ ila 1.×0.10⁻¹ M arasında doğrusal bir yanıt göstermiştir. Tezin son bölümünde, yüzey baskılı elektrot ile iyon tespitinde damla buharlaşmasının duyarlılığa etkisi incelenmiştir. Sonuçlar, 1.0×10⁻⁵ M'den düşük iyon konsantrasyonlarının doğrusal yanıt vermediğini ve damla buharlaşma yönteminin tercih edilmediğini ortaya koymuştur.
  • Doctoral Thesis
    Synthesis and Characterization of Near-Infrared (nir) Emissive Conjugated Polymer Dots for Tumoroid Imaging
    (01. Izmir Institute of Technology, 2024) Karabacak, Soner; Yıldız, Ümit Hakan
    This thesis describes the synthesis and characterization of near-infrared (NIR) emissive conjugated polymers and their polymer dots (Pdots). The Pdots were exploited to image the tumor cells and tumor spheroids. The penetration behavior of NIR emissive Pdots was characterized in five different tumor spheroid models. Three different polymerization techniques were tried to synthesize the NIR emissive polymers, namely oxidative, direct arylation, and Stille polymerization. The obtained NIR emissive polymers underwent structural and optical characterization. P1 was chosen as a model polymer to obtain Pdots from NIR emissive polymers for imaging tumoroids. Pdot preparation includes using ultrasonic emulsification to modify nonionic D-A-D type alkoxy thiophene-benzobisthiadiazole-based conjugated polymers (P1) with amphiphilic cetyltrimethylammonium bromide (CTAB). The technique yields Pdots with a significant positive surface charge of +56.5 mV ± 9.5 and an average hydrodynamic radius of 12 nm. Optical characterization reveals that these Pdots were found as emissive in the NIR region, with a maximum wavelength of 860 nm. These Pdots possess colloidal and optical properties that make them appropriate for use as fluorescence emissive probes in bioimaging applications. The advantageous use of positively charged Pdots has been proven in diffusion-limited settings such as tissues, specifically in certain tumor spheroid models produced from the tumoroid cell lines. After the fluorescence imaging analysis, the Pdots' emission intensity profile indicates that they have high penetration capability into the tumoroid models' center parts. The results show that Pdots with a single-chain donor-acceptor polymer structure that has been cationized with CTAB can penetrate through dense materials over about 1 μm. This provides valuable insights into the progression of targeted theranostic strategies in cancer therapy.
  • Doctoral Thesis
    Preparation of Nanostructured Interface by Polymer Grafting on Various Solid Substrates for Biosensor Applications
    (Izmir Institute of Technology, 2021) Özenler, Sezer; Yıldız, Ümit Hakan
    This thesis presents the utilization, various applications, and characterization of the soft material-based coating formed on the gold surface with varying thickness and chemical properties resulting from the isocyanate-gold interaction. Theoretical calculations regarding the interaction of isocyanate with the gold surface revealed the character of the bond formed and the orientation of the functional groups on the surface. Results by X-ray photoelectron spectroscopy showed the tendency to shift to the high energy at N 1s and C 1s binding energies in the gold-interacting isocyanate group. In the next steps, the isocyanate-activated gold substrate was subjected to sequential incubation of 1,4-butanediol/hexamethylene diisocyanate, and thin-film formation was achieved by surface assisted (SurfAst) urethane polymerization. It was revealed with three different applications that a nano-porous polyurethane (PU) structure was formed on the gold substrate and could be postmodified by using SurfAst polymerization method. In the first application, modification with polyethylene glycol (PEG) was provided to obtain antifouling properties. The PEG-terminated PU structure on the gold surface was shown to reduce protein adhesion by approximately ten-fold. In the second application, SurfAst was applied on the 11-mercaptodecanoic acid incubated surface and grafting onto the poly (N-allyl-N-methyl-N-(3-((4-methylthiophen-3-yl)oxy)propyl) prop-2-en-1-aminium surface was characterized. As a result of PT grafting, PT nanowires with an average height of 100 nm, a width of 250 nm, and a length of 7 μm were obtained on the gold surface. In the last application, a soft nanogel was obtained by a reactive layer-layer (rLBL) coating method using the aza-Michael addition reaction of branched polyethyleneimine and polyester on the isocyanate functional surface. The mechanical and electrical permeability and coating properties of the nanogel layer were assessed. In conclusion, the high potential of isocyanate in surface activation has been demonstrated theoretically and experimentally. Effective modification of gold surfaces by polymer grafting with the SurfAst method and rLBL coating techniques has been achieved.