Zehra Banu Bahşi

A Novel Label-Free Optical Biosensor Using Synthetic Oligonucleotides from E. coli O157:H7: Elementary Sensitivity Tests

SiO2-TiO2 thin films for use as fiber optic guiding layers of optical DNA biosensors were fabricated by the sol-gel dip coating technique. The chemical structure and the surface morphology of the films were characterized before immobilization. Single probe DNA strands were immobilized on the surface and the porosity of the films before the hybridization process was measured. Refractive index values of the films were measured using a Metricon 2010 prism coupler. On the surface of each film, 12 different spots were taken for measurement and calculation of the mean refractive index values with their standard deviations. The increased refractive index values after the immobilization of single DNA strands indicated that immobilization was successfully achieved. A further refractive index increase after the hybridization with target single DNA strands showed the possibility of detection of the E. coli O157:H7 EDL933 species using strands of 20-mers (5′-TAATATCGGTTGCGGAGGTG -3′) sequence.

DNA Biosensors for E. Coli O157:H7 Detection in Drinking Water Resources Using Sol-Gel Derived Waveguides

SiO2 -TiO2 thin films were fabricated by sol-gel dip coating technique to be used as the fiber optic guiding layers of optical DNA biosensors. The chemical structure of the films was examined by Fourier Transformed Infrared Spectroscopy (FTIR, Bio – Rad Tropical Option for FTS 175 C) and the surface morphology of the films was observed by Scanning Electron Microscopy (SEM, Philips XL 30 SFEG). The probe DNA was immobilized on the surface and the pores of the waveguide films before the hybridization process was carried out. By using Metricon 2010 prism coupler, 12 different spots were determined to be measured. Then the mean refractive index values and their standard deviations were calculated. The increased refractive index values after the DNA immobilization indicated that immobilization was successfully achieved. Further increase after the hybridization with complementary DNA showed the possibility of detection of the E. coli O157:H7 EDL933 species by using 20-mers (5’- TAATATCGGTTGCGGAGGTG-3’) sequence of GeneID: 957271.

Sintering behavior of ZnO: Mn ceramics fabricated from sol-gel derived nanocrystalline powders

Abstract Undoped and Mn doped ZnO ceramics, sintered at 1200 °C, were produced from sol-gel derived nanocrystalline powders calcined at 750 °C. Mn doped powders showed trace amounts of spinel (ZnMn2O4) phase in addition to a dominant zincite phase, while Mn doped ceramics were comprised solely of zincite structure. X-ray mapping of the powders did not reveal any Mn concentrated areas, indicating that the ZnMn2O4 phase was homogeneously distributed with a very small grain size. The grain size of the undoped powders was around 50 nm, and there was a minor increase in the grain size when powders were doped with Mn. Undoped ceramics exhibited grain sizes distributed in the range 2 – 10 μm while Mn doped ceramics displayed slightly smaller grains. Relative densities of the undoped and Mn doped ceramics were measured as 0.695 and 0.950, respectively.

Sol-Gel Fabrication of Lithium Doped Zinc Oxide Thin Films

Li doped zinc oxide thin films were deposited on glass substrates by a sol-gel technique. Acetates of zinc and lithium were used as metal sources. A homogeneous and stable solution was prepared by dissolving acetates in the solution of 2-propanol and ethanolamine. ZnO:Li thin films were obtained after preheating the spin coated films at 250 C for 1 minute after each coating. A post annealing between 450-600 C was applied after the deposition of the last layers. XRD analysis revealed ZnO with zincite structure (Card no: 36-1451) in all films. The thickness of the films was measured as 75 nm per layer. The optical band gap of the films increased as doping concentration of Li increased and decreased as the post-annealing temperature increased.