No description available.

Electron transport in purple bacteria was studied using combination of absorption spectroscopy and induced bacteriochlorophyll fluorescence in whole cells in vivo. Focus is placed on relations between fluorescence yield, the state of the electron transport chain and the membrane potential. A laboratory-built absorption spectrophotometer-fluorimeter is described.

DNA-modified surfaces have been widely studied for microarray and biosensor applications, in particular sequence-specific detection of DNA, for which electrochemical and optical signs can be produced. Variations in the organization and surface density of adsorbed DNA are known to affect the sensitivity and reliability of assays performed using such surfaces, however most measurements of such surfaces to date have little to no spatial resolution, limiting the information that can be gathered regarding the heterogeneity of the organization of adsorbed DNA molecules. We have applied in situ epi-fluorescence microscopic imaging in conjunction with electrochemical measurements to fluorescently labelled thiolate DNA, adsorbed on polycrystalline gold electrodes with a mercaptohexanol (MCH) passive layer. Spatially resolved information on the organization of adsorbed DNA on the surface is gathered within an area measuring 520by 730micrometres with a 0.96 micrometre resolution. The technique has enabled us to investigate "hotspots" (regions of anomalously bright fluorescence) and regional variation in fluorescence; since molecular fluorescence is quenched as a function of distance from the metal substrate, potential modulation with consequent DNA reorientation or layer specificity of the adsorption. Furthermore, an alternative means to the conventional preparation of thiolate-DNA / MCH monolayers has been developed. In this new method, a gold substrate passivated with MCH is subsequently immersed in an aqueous solution of 5'hexylthiol modified DNA. Through a ligand exchange process, DNA is immobilized forming a mixed MCH / DNA monolayer. Samples prepared via the new method display fewer hotspots and improved fluorescence switching of the DNA during electromodulation for samples made with single stranded (ss) DNA and with double stranded (ds) DNA. Measurement of the DNA surface concentration using ruthenium (III) hexaammine chloride with cyclic voltammetry for self assembled monolayers (SAMs) prepared via the new method are on the order of 1% of the maximum grafting density obtainable for both ssDNA and dsDNA by conventional methods. / Science, Faculty of / Chemistry, Department of / Graduate

The aim of the research was to use the principles of immunoassays and fluorescence spectroscopy to detect the presence of 4-amino-N-(4,5- dimethyl-2-pyrimidinyl)benzenesulfonamide, commonly known as sulfamethazine, in food.

Class of 2015 Abstract / Objectives: To develop an assay to permit the identification of compounds that can inhibit the interaction between GIT1 and the amino-terminal SH3 domain (SH3-N) of GRB2. Methods: The GIT1 protein was expressed in Sf9 insect cells and purified using Talon resin beads. The SH3-N domain of GRB2 was expressed in the E. coli strain, BL21(DE3)pLysS, and purified using glutathione resin beads. The SH3-N domain was fluorescently tagged on cysteine 32 using Cyanine 3 maleimide. The fluorescence of the assay was measured by using a plate reader with excitation wavelength of 555 nm and emission wavelength of 570 nm. Results: The GIT1 protein was expressed in Sf9 cells and purified using the Talon beads. The SH3-N domain of GRB2 was expressed in BL21 cells and purified from the glutathione resin beads. The SH3-N domain was cleaved from GST by using thrombin, which was engineered into the GST fusion protein and were fluorescently labeled using Cyanine 3 maleimide. Conclusions: The fluorescence polarization assay that will detect the interaction between GIT1 and the SH3-N domain of GRB2 is still under development, but it has progressed towards completion since both components of the assay are in hand.

No description available.

No description available.

The fluorescence and absorption spectra of anthracene in the near ultra-violet were investigated in n-heptane, fluorene, biphenyl and n-hexane matrices at low temperature. The assignment of the excited electronic state as ‘Biu was confirmed. In the ground electronic state eight Qg and five b₃g, and in the 'Bᵢᵥ upper electronic state seven Qg and five b₃g fundamentals were assigned. It was deduced that the potential surfaces of the 'Ag and the 'Bᵢᵥ states were similar in shape as there was an approximate agreement between the values of corresponding fundamental vibrations in the two electronic states. The potential surfaces were unusually harmonic for a polyatomic molecule, at least along the normal co-ordinates available to this study. No evidence for the presence of anharmonicity was found in even the highest overtone (the third) measured, although several possible examples of Fermi resonance between vibrational modes were observed both in fluorescence and in absorption. The Fermi resonances were assigned primarily on the basis of intensity transfer between lines rather than line shifts. The presence of a weaker long-axis polarized transition ( 'B₂ᵥ- 'Ag ) in anthracene predicted by theory was not detected. The lowest energy electronic transition in fluorene was found to be polarized along the long axis of this molecule. / Science, Faculty of / Chemistry, Department of / Graduate

Evidence that recoilless emission and absorption exist may be shown by an experiment in which the source gamma rays are allowed to pass through a suitable absorber to a detector.

Please read the abstract (summary) in the section 00front of this document. / Thesis (PhD)--University of Pretoria, 2011. / Food Science / unrestricted