Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
Browse
2 results
Search Results
Doctoral Thesis Dna Adsorption on Silica, Alumina and Hydroxyapatite and Imaging of Dna by Atomic Force Microscopy(Izmir Institute of Technology, 2013) Yetgin, Senem; Balköse, Devrim; Balköse, DevrimThe scope of the study is to investigate calf thymus DNA adsorption process on solid powders such as silica, alumina and hydroxyapatite (HAP) to improve DNA solid phase extraction efficiency and to visiulize DNA adsorption by atomic force microscopy (AFM). The equilibrium and kinetics of the DNA adsorption were investigated in batch adsorption on a commercial silica gel and a synthesized silica aerogel, commercial alumina and HAP powders from aqueous DNA solution. Commercial DNA extraction kit adsorbents were also characterized and used for adsorption. Adsorbed DNA was imaged in ambient air on flat surfaces of mica, silica and alumina wafers and HAP particles coated glass surfaces and a HAP pellet surface by AFM. Effects of ambient air, nitrogen flow and freeze drying methods on DNA morphology on the releted surfaces were also investigated. Adsorption of DNA on silica, alumina and HAP increased with the decrease of pH from 9.0 to 2.0. Enhancements of the adsorption capacities of adsorbents were obtained with the addition of MgCl2. It was found that the Van der Waals and the hydrogen bonds rather than the surface charge were the cause of the adsorption. The adsorption isotherms of DNA on silica, alumina and HAP were fitted to Langmuir model in pH range 2-9. The adsorption kinetics obeyed pseudo second order model. The sharpest image of DNA by AFM was obtained by freeze drying method on alumina surface. Dispersed DNA in water was adsorbed on the surfaces not as single molecules but as supercoils consisting of many molecules.Doctoral Thesis Estimation of the Surface Charge Distribution of Solids in Liquids by Using Atomic Force Microscopy(Izmir Institute of Technology, 2011) Yelken Özek, Gülnihal; Polat, MehmetColloidal systems are widely encountered in minerals, ceramics, environment, biology, pharmaceuticals and cosmetics industries. These systems consist of micronsized particulates dispersed in a solvent. Homogeneity, dispersibility, stability of colloidal systems determines the economy and success of the final product in these applications. Control and manipulation of these properties depend on detailed analysis of the interactions among the particles. Electrophoretic potential measurements or colloidal titration methods are widely employed to characterize the charging of colloidal systems. However these methods only yield average charging information, not the charge distribution on the surface. Atomic Force Microscope (AFM) allows topographic surface analysis at nanometer level resolutions. Though it is widely used to obtain derived information AFM directly measures the forces between the tip and the surface atoms. The objective of the present work is to assess the applicability of AFM to surface charge mapping, i.e., the detection of positive or negative charged regions on metal oxide surfaces. Hence, well defined tips were prepared and allowed to interact with well defined oxide surfaces under different pH conditions. The influence of solution ion concentration and pH on the forces measured was also investigated. These measured force-distance curves were analyzed using a new solution of the one dimensional Poisson-Boltzmann equation to isolate the electrical double layer force, hence the surface charge on each measurement point. The new solution in question provides analytical expressions for all charging conditions which are amenable to such analysis.Repetitive force measurements on a predefined grid on the solid surface ultimately yield the charge distribution of the surface. Such an analysis procedure is new and advances the charge measurements on solids in solution to a new level.