Manyetik bifonksiyonel nano kompozitlerin sentezlenmesi, karakterizasyonu ve uygulamaları
Synthesis, characterization and applications of magnetic bifunctional nano composites
Yazar: BARIŞ HULİSİ KARAKUŞ
Danışman: DOÇ. DR. ESRA ALVEROĞLU DURUCU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Fizik Ana Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Fizik ve Fizik Mühendisliği = Physics and Physics Engineering

Özet:
Manyetik demir oksit nanoparçacıkları, boyuta bağlı manyetik ve elektronik özellikleri ve birçok alanda kullanılabilmeleri nedeniyle üzerine oldukça fazla çalışılan bir konu haline gelmişlerdir. Bu parçacıklar nano boyutlara ulaştığında bulk haldeki özelliklerinden oldukça farklı özellikler gösterirler. Bu parçacıklar ferro akışkanlarda, veri depolamada, hücre işaretlemede ve biyo-ayrıştırma gibi uygulamalarda şu anda kullanılmaktadır. Ferrite nanoparçacıklarının üretimi üzerine yapılan araştırmalar, var olan tekniklerde gelişmeler yaratmış olsa da bu parçacıkların üretimleri sonrasında kimyasal dengede kalamamaları hala bir problemdir. Bu nedenle bazı uygulamalarda kullanılabilmeleri için üzerlerine kaplama yapılması gerekmektedir. Kaplama malzemesi olarak en uygun malzemelerden birinin silika olduğu görülmüştür.
Nanojeller, hidrojel ve nano materyallerin özelliklerini barındıran, nano boyuttaki hidrojel parçacıklarıdır. Yüksek su içeriği, ayarlanabilir kimyasal özellikleri ve fiziksek yapıları sebebiyle biyomedikal alanda yaygın kullanıma sahiptirler. Biyomedikal alanda en çok kullanılan malzemeler ısıya duyarlı hidrojellerdir. Vücut içerisinde de uygulanmaya elverişli olan ısıya duyarlı hidrojellerin başında N-isopropyl acrylamide (NİPA) jeli gelmektedir. Kritik sıcaklığı olan 32oC'nin üzerinde PNİPA jeli büzüşmekte ve bu sıcaklığın altında ise içine çözelti absorblayabilmektedir. 
Bu tez kapsamında, çalışmanın ilk kısmında ZnS:Fe3O4 bifonksiyonel nanoparçacıkları sentezlenmiştir. Alınan UV-Vis absorpsiyonu, XRD, FTIR, VSM ve SEM ölçümleri sonucunda ZnS ve Fe3O4 nanoparçacıklarının boyutları sırasıyla 5 nm ve 12 nm olarak bulunmuş, MPS kaplı ZnS nanoparçacıklarının Fe3O4 ile Si-O-Si bağlarının meydana geldiği ayrıca ZnS:Fe3O4 nano kompozitinin süper paramanyetik özellik gösterdiği gözlemlenmiştir. Tezin ikinci kısmında ise, üretilen Fe3O4:PNİPA kompozit nano malzemesi lizozim adsorpsiyonu için kullanılmıştır. XRD, FTIR, AFM ve SEM ölçümleri nanojel-nanoçubuk kompozitinin başarılı bir şekilde elde edildiğini göstermiştir. VSM ölçümleri, çubuk şeklindeki Fe3O4 parçacıklarının süper paramanyetik olduğunu ve SEM ölçümleri ise nano çubukların ortalama boyutlarının 200 nm ile 300 nm arasında olduğunu göstermiştir. Lizozim adsorpsiyonu floresans ölçümleri ile takip edilmiştir. Maksimum adsorpsiyonun 450 sn'de tamamlandığı gözlemlenmiştir.

Abstract:
Magnetic iron oxide nanoparticles have been widely studied due to their size dependent magnetic and electronic properties and their potential applications in many areas. They show unique properties when they reach to nano size. This cause them useful for different areas. Magnetite (Fe3O4) is the most studied one among the other ferrites, and Fe3O4 nanoparticles have been studied on the application in ferrofluids, data storage, magnetic imaging techniques, labeling of cells, biosensors and also bio-separation processes. In last decades, Fe3O4 nanoparticles have been studied in biomedical area. Synthesize techniques of Fe3O4 nanoparticles and improvements of them have been studied by many researchers but still there are some challenges in their preparation procedures because of their lack of stability. Therefore, Fe3O4 nanoparticles need to be coated to get a surface layer with compatible surface chemistry which helps magnetic nanoparticles to be stabilized and functionalized. Many kinds of materials have been studied for use as a coating layer, such as noble metals, metal oxides and inorganic silica. SiO2 has high chemical stability, amorphous structure, biocompatibility and a wide bandgap. Hence, SiO2 is an ideal matrix or shell material for most of nanoparticles and the toxicity of nanoparticles can be reduced by encapsulating them using a SiO2 shell. Therefore, in many of study, magnetic nanoparticles were produced by coating the SiO2. Most of such studies, SiO2 is produced using tetraethyl orthosilicate (TEOS) by the typical sol-gel method.  
Nanogels are nanosized hydrogel particles that combine the properties of both hydrogels and nanomaterials. They show high water content, tunable chemical and physical structures, good mechanical properties and biocompatibility. It is sterically crosslinked hydrophilic materials of high biocompatibility that can absorb considerable amounts of water and at the same time remain insoluble and retain their structural object, appear to be most talented constituents for drug carrying systems. Due to their tunable size, a large surface area for multivalent bio conjugation, and an internal system for the combination of therapeutics. These distinctive properties offer great possibility for the utilization of nanogels/hydrogels in applications for tissue engineering, biomedical transplants, bio nanotechnology, and drug delivery. The most capable materials are thermo responsive hydrogels, first of all N-isopropyl acrylamide (NİPA) based ones. N-isopropylacrylamide (NİPA) is the most widely studied thermosensitive polymer. It has a Lower Critical Solution Temperature of 32oC. It collapses above the Lower Critical Solution Temperature and expands below the Lower Critical Solution Temperature of the polymer. Due to its well defined and reversible lower critical solution temperature poly (N-isopropylacrylamide) (PNİPA) has been widely studied. PNİPA nanogels and microgels have been synthetized by heterogeneous free radical polymerization methods including inverse microemulsion and, dispersion and miniemulsion. Hydrogel nanocomposites involve the incorporation of nanoparticles with a hydrophilic matrix, which can improve the properties of conventional hydrogel systems.
Lysozyme (N-acetylmuramide glycanhydrolase) is a commercially valuable enzyme for food industry and pharmaceutical applications. It is one of the most important enzymes present in serum and plays a critical role in the enzymatic degradation of biomaterials. Lysozyme is comprised of a single chain of 129 amino acids that, because of hydrophobicity, compacts into an ellipsoidal shape approximately 45Å across. Lysozyme is a protein common to a variety of organisms. The largest concentration of lysozyme is in tears and hen egg albumin is the primary source. Fuertes et al. reported on the immobilization of lysozyme and they showed that lysozyme could be immobilized in core/shell composite containing iron oxide ferrite nanoparticles. Shamim et al.  reported on the adsorption of lysozyme, on thermosensitive poly(N-isopropylacrylamide) coated nanomagnetic Fe3O4 particles. Haynes and Norde reported that adsorbed lysozyme maintains a relatively high internal cohesion on the adsorption of lysozyme and α-lactalbumin on polystyrene and hematite.
In the first part of this thesis, ZnS:Fe3O4 bifunctional nanoparticles prepared via two steps. First, (3-mercaptopropyl) trimethoxysilane (MPS) capped ZnS nanoparticles were synthesized by using solution growth technique. Second, Fe3O4 nanoparticles were synthesized by co-precipitation of Fe+3 and Fe+2 as reaction substrates and NaOH as precipitant, then they were covered with silica by hydrolysis of tetraethyl orthosilicate (TEOS) as the silica source. Separately synthesized MPS capped ZnS fluorescent nanoparticles and SiO2 coated Fe3O4 magnetite nanoparticles were characterized by using UV-Vis Absorption Spectroscopy, Fluorescence Spectroscopy, X-ray analysis, Vibrating Sample Magnetometer and Fourier Transform Infrared Spectroscopy methods. The size of ZnS and Fe3O4 nanoparticles were found 5 nm and 12 nm, respectively. After synthesis and characterization of these two nanostructures, they mixed and stirred at room temperature for 24 hours. It is confirmed by Fourier Transform Infrared Spectroscopy results that the MPS capped ZnS nanoparticles were attached to the surface of the Fe3O4 nanoparticles via Si-O-Si bonds created by the Si-O group of Fe3O4 surface and the trimethoxysilane group of MPS during the stirring process. The final product was separated by an external magnet and washed with several times. The fluorescent-magnetic ZnS:Fe3O4 bifunctional nanoparticles showed that superparamagnetic behaviour and emission light at 380 nm wavelength.
In the second part, Fe3O4:PNİPA composite nano material synthesized, characterized and used for lysozyme adsorption. X-ray analysis, Fourier Transform Infrared Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy measurements show that nanogel-nanorod composite was prepared successfully. Vibrating Sample Magnetometer measurement shows that the Fe3O4 particles in rod shape has superparamagnetic behavior. Scanning Electron Microscopy measurements shows the average of thicknesses of the nano rods was found around 150 nm~200 nm and average particle size of the nano gels was found around 200 nm~300 nm. The Scanning Electron Microscopy measurements images also reveal that the surface of the rods is very smooth. The adsorption kinetic of lysozyme by composite material studied via fluorescence method, and the adsorption reaction rate constant is calculated by using Langmuir-Hinshelwood model. The fluorescence emission spectra were recorded in the range of 310–450 nm upon excitation at 300 nm. Lysozyme molecule emits a broad peak at the maximum emission at 345 nm. This wavelength is selected to follow the changes in the emission intensity, which is decreases in time because of the adsorption of lysozyme molecules by the Fe3O4–nanogel composite material. The experiments performed after every 15 seconds show that maximum adsorption occured in 450 seconds. Fe3O4:PNİPA Nanorods-Nanogel composite was found as a fast catalyst for lysozyme like protein immobilization.