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Theses and dissertations (Applied Sciences)

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    Fabrication of electrochemical biosensors for the determination of phenolic compounds by experimental and computational methods
    (2018) Kunene, Kwanele Winterose; Bisetty, Krishna; Kanchi, Suvardhan
    The polyphenolic compounds of interest, bisphenol A (BPA) and its analogue bisphenol S (BPS) used in the plastic industry to manufacture baby bottles and beverage containers, were used in this study. They are generally used in the manufacture of polycarbonates, epoxy resins and unsaturated polystyrene resins. There is a growing concern in the public and scientific community about these organic compounds due to their endocrine disrupting activity and negative toxic impact on the wildlife. This has encouraged scientists to embark on research to find a sensitive and selective technique that will adequately determine these compounds even in trace amounts. The experimental research strategy adopted in this work was supported by computational methods. This work was conducted in two stages; Firstly, a sensitive EC biosensor was developed using a carbon screen printed electrode fabricated with the combination of silver doped zinc oxide nanoparticles with multiwalled carbon nanotubes (MWCNTs) and laccase enzyme. The EC behaviour of BPA towards the fabricated biosensor was investigated using cyclic voltammetry and differential pulse voltammetry under optimum experimental conditions. Secondly, a novel and selective PEC sensor was developed for the first time to detect BPS based on the vertically aligned ZnO nanorods (ZnO NRs) with a molecularly imprinted polypyrrole (PPy). Amperometric, cyclic voltammetry and impedance spectroscopy were used for the investigation of the photo induced electrochemical behaviour of BPS. Different characterisation techniques such as ultra-violet visible spectroscopy, fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, photoluminescence, Raman spectroscopy, grazing incidence X-ray diffraction and diffuse reflectance were used to characterize the synthesized nanostructures. Results revealed that the fabricated EC and PEC sensors exhibited good catalytic activity towards the determination of BPA and BPS respectively, in samples extracted from plastic water bottles. For the EC method, a low detection limit of 0.08 μM for BPA in a linear range 0.5 to 2.99 µM was detected. However, in the case of BPS, a highly selective PEC method was attained linearly ranging from 2.5 to 12.5 µM with a much higher limit of detection of 0.7 μM. Experimental results were further supported computationally for a better understanding of the optical properties of ZnO NRs-polypyrrole complex. Computational results were in good agreement with experimental results.