Sol-gel processing routes for encapsulation of double stranded DNA in solid porous silica hosts have been established. The encapsulation was carried out in two steps: hydrolysis of a silica-forming alkoxide-based sol was followed by condensation/gelation to a solid form upon addition of a buffer solution containing DNA molecules. The effects of gelation chemistry and DNA amount on chemical and microstructural properties of resultant silica matrices and on DNA encapsulation efficiency were investigated. The analytical characterization was performed by UV-vis spectroscopy, 29Si nuclear magnetic resonance spectroscopy and by nitrogen adsorption studies. It was demonstrated that DNA incorporation had a pH-dependent catalytic effect on gelation kinetics and promoted silica network completion. In addition, the scale of porosity and the average pore size of the resultant silica increased with gelation pH and also with DNA-buffer solution in the starting sol-gel formulation. The chemistry-derived pore size variation controls the DNA encapsulation efficiency in the silica matrices and the DNA holding capacity strongly depends on the scale of the porosity attained. The selective adsorption of ethidium bromide- a DNA-intercalative reagent molecule- on DNA-silica gels confirmed that the DNA molecules remained entrapped within the silica host in their native state without any deterioration. Besides pure silica, amine-functionalized hybrid silica hosts were also formed by sol-gel. The hybrid gels were found not to be suitable for DNA encapsulation, as these matrices dissolve in aqueous environment due to incomplete silica network formation. The DNA-doped silica hosts may provide promising matrices for development of biosensors, bioreactors and bioassay platforms.

Titanium dioxide (TiO2), a semiconductor, has been used in many areas like heterogeneous photocatalysis. In the present study, the effect of hydrothermal treatment conditions and the use of carbon nanotubes on the photocatalytic activity of sol-gel synthesized titanium dioxide were examined. The anatase particles were transformed into layered trititanate particles with either nanotube or nanoplate structure by hydrothermal treatment under the alkaline conditions. Post hydrothermal treatment under neutral conditions was also applied and mesoporous particles were transformed into nanostructured, highly crystalline and ordered anatase particles. Photocatalytic activities of hydrothermally treated samples were determined against Escherichia coli under solar irradiation. Results showed that hydrothermal treatment under alkaline conditions improved the photocatalytic activity. However, although being highly crystalline, after post treatment, a limited activity was obtained because of dehydration of active (101) face of anatase. Nevertheless, TiO2&amp / #8217 / s initial inactivation constant rose from 0.6 to 2.9 hr-1 after regeneration of active sites in aqueous medium under solar irradiation. In order to enhance the surface area and improve activity, multi-walled carbon nanotubes were utilized during the synthesis of TiO2. The effect of calcination conditions and presence of sodium, iron and cobalt on the photocatalytic activity were also studied. For these samples, photocatalytic activities were tested with methylene blue solution under UV irradiation. It was observed that the utilization of CNTs enhanced both the surface area and the activity. Compositions with highest CNT content had better activities for their ability to delay charge recombination. While pure TiO2&amp / #8216 / s initial decomposition constant was 0.8 hr-1, with sodium doping the best value of 1.9 hr-1 was achieved.

The aim of this study was to investigate the viability of patterning by immobilization, photocatalytic removal, and re-immobilization steps of the enzyme on photocatalytically active thin films for biosensor fabrication purposes. For this aim, TiO2-SiO2-Au sol-gel colloids were synthesized and deposited on glass substrates as thin films by dip coating. Cysteamine linker was assembled on gold nanoparticles to functionalize thin films with amine groups for immobilization of model enzyme invertase. Effect of immobilization temperature, enzyme concentration of the immobilization solution and immobilization period on invertase immobilization were investigated. The immobilized invertase activity was found independent from the immobilization temperature in the range tested (4oC-room temperature). The optimum enzyme concentration and period for immobilization was determined as 10&micro / g/ml and 12 hours respectively. The resulting invertase immobilized thin films showed high storage stability retaining more that 50% of their initial activity after 9 weeks of storage. Photocatalytic enzyme removal and re-immobilization studies were carried out by irradiating the invertase immobilized thin films with blacklight. Upon 30 minutes of irradiation, immobilized invertase was completely and irreversibly inactivated. Initial immobilized invertase activity (before the irradiation) was attained when invertase was re-immobilized on thin films that were irradiated for 5 hours. Thus it was inferred that with sufficient exposure, enzymes can be completely removed from the surfaces which makes the re-immobilization possible. The possibility of enzyme removal with photocatalytic activity and re-immobilization can pave the way to new patterning techniques to produce multi-enzyme electrode arrays.

The aim of this study was to immobilize the redox enzyme laccase over TiO2-SiO2-Au thin film coated ITO glass substrates in order to prepare electrochemically active surfaces for biosensor applications. Colloidal TiO2-SiO2-Au solution was synthesized by sol-gel route and thin film was deposited onto the substrates by dipcoating method. The cysteamine was utilized as a linker for immobilization of enzyme covalently through gold active sites. Preliminary studies were conducted by using invertase as model enzyme and Pyrex glasses as substrates. The effect of immobilization parameters such as immobilization temperature, concentration of enzyme deposition solution, immobilization time for laccase were examined. Leakage studies were conducted and storage stability of immobilized laccase was determined. Highest laccase activity was achieved when immobilization was performed with 50 &micro / g/ml solution at 4&deg / C for 2 hours. Laccase activity decreased after 4 hours of impregnation in enzyme solution. Laccase leakage was observed in the first usage of substrates and 55% activity decrease was determined in the subsequent use which might be attributed to the presence of uncovalently adsorbed enzyme on the fresh samples. In air and in buffer storage stabilities were also tested. It was found that the activity of samples almost vanished after 6 days regardless of storage conditions. Both enzymes had more activity on ITO substrate.

The aim of this study is to produce maghemite nanoparticles by using different production methods. To achieve this purpose Sol-Gel Processing and Microwave Synthesis methods were employed. Suitable characterization techniques like XRD, TEM, BET, and VSM were performed to control the properties of the synthesized particles whether they are suitable for certain applications. In the sol-gel part of the study two different routes were employed to obtain maghemite nanoparticles. In the first route TEOS (tetraethoxysilane) was used as the precursor. Approximate particle sizes of these samples lie between 12.0-23.4 nm. From the magnetization measurements saturation magnetization (Ms) values are obtained between 4-12 emu/g. In the second route of the sol-gel method ethylene glycol and diethylene glycol were used as starting materials. Ms value was found as 28 emu/g for the ethylene glycol sample as the highest magnetization value due to having the highest amount of maghemite phase. The superparamagnetic behavior observed in these samples was tried to explain by curve fitting. Langevin and tangent hyperbolic functions were used to fit the magnetization curves. From the XRD study particle sizes of these samples lie in the 4.0-48.5 nm range and these results are consistent with the size distributions obtained from the TEM study. In the last part of the study microwave method was used to produce maghemite nanoparticles. Most of the samples contain maghemite and hematite phases together and particle sizes were between 3-30 nm. Ms values of these microwave samples were lower than that of the sol-gel samples with a value about 3.0 emu/g. Keywords: Maghemite, nanoparticle, superparamagnetism, sol-gel, microwave

Propylene oxide (PO) is an important raw material for the chemical industry, which is produced commercially by the chlorohydrin process and hydroperoxide process. However the deficiencies in these processes have given rise to considerable interest in the development of a direct route to PO that does not produce by-products or coproducts. The development of novel, active and selective catalysts for gas phase oxidation of propylene using molecular oxygen were studied via testing a large number of catalysts by high-throughput screening method over combinatorially prepared different catalytic system in this study. v The promoted and un-promoted silver (Ag), copper (Cu), manganese (Mn) mono and bimetallic catalytic system over high and low surface area silica, alumina, titanium oxide and titanium-silicate supports were prepared by single step sol-gel method and by incipient wetness method. The study to determine the most effective catalyst and promoter in the epoxidation reaction with different reaction conditions, showed that potassium (K)- promoted Cu metal supported over high surface area silica favored the PO production at a high reaction temperature (350 &deg / C) and oxygen rich atmosphere (C3H6/O2=1.0). The catalyst showed high and low propylene oxide productivity was investigated by some of the characterization techniques. The highlydispersed copper particle over silica support was determined by XRD, TEM and XPS techniques. The only change between promoted and un-promoted catalyst was found out in the temperature dependence of propylene consumption and PO production rate. It was inferred that potassium (K) only neutralizes the acid sites of silica.

Metal coordinated polymer nanocomposites have gained great attention due to their superior characteristics. Polymethylmethacyrlate (PMMA) is the most commonly used polymer since it is easily processed. In this study, modified TiO2 nanoparticles prepared by insitu and exsitu methods were embedded into PMMA in order to improve its thermal stability and the effects of TiO2 nanoparticles on thermal characteristics of PMMA were investigated by direct pyrolysis mass spectrometry. The insitu method which is a sol gel method, TiO2/SiO2 nanoparticles were synthesized by mixing titanium(IV) tetraisopropoxide, TTIP, with silane coupling agent, 3-(3-methoxysilyl)methylmetacrylate, MSMA in absolute ethanol. In exsitu method, TiO2 powder was directly mixed with silane coupling reagent. TiO2/SiO2 nanoparticles were embedded into the PMMA by direct mixing resulting in exsitu and insitu TiO2/SiO2/PMMA nanocomposites. The synthesized TiO2/SiO2/PMMA nanocomposites were characterized by TEM, ATR-FT-IR and analyzed for the investigation of their reaction mechanism and thermal characteristics by pyrolysis mass spectroscopy. iv TEM images confirmed the formation of TiO2/SiO2 nanoparticles and TiO2/SiO2/PMMA nanocomposites and indicated that the average particle size of TiO2/SiO2 nanoparticles was around 6 nm whereas average particle size of SiO2/TiO2/PMMA nanocomposites were around 25 nm. The increase in the size of nanoparticles is associated with incorporation of TiO2/SiO2 nanoparticles into PMMA matrix. ATR-FTIR spectrum of 5% TiO2/SiO2/PMMA nanocomposites showed the formation of TiO2/SiO2 nanopartciles clearly. Pyrolysis mass spectrometry analysis revealed that incorporation of TiO2/SiO2 nano- particles into PMMA resulted in higher thermal stability only for low weight percentage insitu TiO2/SiO2/PMMA. At high weight percentages a decrease in thermal stability was detected. On the other hand, in case of exsitu TiO2/SiO2/PMMA, contrary to our expectations a decrease in thermal stability was detected. The decrease in thermal stability was attributed to evolution of methacrylic acid during thermal degradation of silane groups.

Indium tin oxide (ITO) thin films have been used as transparent electrodes in many technological applications such as display panels, solar cells, touch screens and electrochromic devices. Commercial grade ITO thin films are usually deposited by sputtering. Solution-based coating methods, such as sol-gel however, can be simple and economic alternative method for obtaining oxide films and also ITO. In this thesis, &ldquo / ITO sols&rdquo / and &ldquo / ITO nanoparticle-incorporated hybrid ITO coating sols&rdquo / were prepared using indium chloride (InCl3

Ion-sensitive field effect transistors (ISFET's) have many advantages than the conventional ion selective electrode. Small size, fast response and compatible with conventional IC technologies were the most important advantages. The general structure of ISFET was the same with MOSFET, but the main difference is that the metal gate in MOSFET was replaced by reference electrode/electrolyte/insulator(ionic sensor membrane) structure in ISFET. The insulator surface will suffer the change of potential as the is sample immersed into electrolyte, by which, we can measure the pH or other ionic concentration. In this thesis the amorphous lead titanate (a-PbTiO3) thin film was prepared by sol-gel method to be the sensor gate of ISFET. The lead titanate thin films were deposited on SiO2(1000Å)/p-Si substrates, and the EIS structure was obtained. The flat-band voltage(£GVBF) can be shifted by C-V measurement. The optimum conditions were found that the firing temperature was about 4000C and thin film thickness was about 0.5

The thin film deposition system using ultrasonic nebulization was adopted in this study. SnCl4.5H2O, SbCl3, and TaCl5 were used as solutes. Ethanol was used as the solvent. Solutions of different Sn4+ concentration, Sb concentration (Sb/Sn atomic ratio) in Sn, and Ta concentration (Ta/Sn atomic ratio) in Sn were mixed. The mist was generated from a solution by the agitation of an ultrasonic device operating at about 1.65MHz. The mist was carried to the heated substrate (corning 7059 glass) by the flow of nitrogen gas so that it was decomposed by heat. SnO2-x films were deposited on the substrate due to the pyrolysis reaction. The experiment included six series: Sn4+ concentration series, Sb-doping series, temperature series, Ta-doping series, aging time series and nebulization rate series. SnO2-x films were analyzed by XRD, UV-Visible, SEM, and Hall-measurement. The optimum deposition conditions were obtained through analyses of these six series. The film deposition rate of nonaged solution was faster than aged solution. When the nebulization rate of solution was 1.6 ml/min, the resistivity of undoped SnO2 film obtained with the substrate kept at 450 oC is 2.364¡Ñ10-2£[-cm and the maximum transmittance of the visible light is 78.7%. When Sb/Sn atomic ratio in the solution was 2%, the resistivity of Sb doped SnO2 film obtained with the substrate kept at 525 oC is 2.77¡Ñ10-3£[-cm and the maximum transmittance of the visible light is 71% . When Ta/Sn atomic ratio in the solution was 0.1%, the resistivity of Ta doped SnO2 film obtained with the substrate kept at 450 oC is 3.917¡Ñ10-2£[-cm and the maximum transmittance of the visible light is 85% In this study, the electro-optical properties of Sb and Ta doped SnO2 thin films derived from an ultrasonic nebulization process were reported and discussed carefully through film characterizations.