Browsing by Author "Nxusani, Ezo"

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    Novel 3-mercaptopropionic acid capped iridium selenide quantum dots modified electrochemical immunosensor for the detection of fish toxin, nodularin
    (University of the Western Cape, 2012) Nxusani, Ezo; Iwuoha, Emmanuel; Baker, Priscilla
    A novel 3-mercaptopropionic acid capped iridium selenide quantum dots based label free impedimetric immunosensor was successfully constructed. The 3-mercaptopropionic acid capped iridium selenide quantum dots synthesized were studied using HRTEM, revealing the formation of very small sizes, of about 3 nm. The optical Uv-Vis absorption wavelength of the quantum dots is blue-shifted, a phenomenon explained by the effective mass approximation (EMA) for semiconducting materials with sizes below 10 nm. Using cyclic voltammetry it is noted that the quantum dots have interesting electro-catalytical properties. The immunosensor proved to be sensitive towards nodularin, with a very low detection limit of 0.009 ng/mL and is significantly lower than the recent anti-nodularin ELISA kit developed by (Zhou et al., 2011) which has a detection limit of 0.16 ng/mL.Also the dection limit of the immunosensor is below the South African guideline value for microcystin-LR (0-0.8) μg/L (DWAF; 1996). The calibration curve of the 3MPA-GaSe nanocrystal based biosensor was successfully constructed, which exhibited a trend described by Michaelis-Menten, a typical behaviour of enzymatic biosensors. The detection limit of the biosensor is 0.004 nM and is significantly lower than the action limit of 17beta-estradiol, (1.47 x 10-10 M).
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    Synthesis and analysis of Novel Platinum group Metal Chalcogenide Metal Quantum Dot and Electrochemical Markers
    (University of the Western Cape, 2018) Nxusani, Ezo; Iwuoha, Emmanuel I
    Although cadmium and lead chalcogenide quantum dot have excellent optical and photoluminescent properties that are highly favorable for biological applications, there still exists increasing concerns due to the toxicity of these metals. We, therefore, report the synthesis of new aqueous soluble IrSe quantum dot at room temperature utilizing a bottom-up wet chemistry approach. NaHSe and H2IrCl6 were utilized as the Se and Ir source, respectively. High-resolution transmission electron microscopy reveals that the synthesized 3MPA-IrSe Qd are 3 nm in diameter. The characteristics and properties of the IrSe Qd are investigated utilizing, Selected Area electron diffraction, ATR- Fourier Transform Infra-Red Spectroscopy, Energy Dispersive X-ray spectroscopy, Photoluminescence, Cyclic Voltammetry and chronocoulometry. A 3 fold increase in the optical band gap of IrSe quantum dot in comparison to reported bulk IrSe is observed consistent with the effective mass approximation theory for semiconductor materials of particles sizes < 10 nm. The PL emission of the IrSe quantum dot is at 519 nm. Their electro-activity is studied on gold electrodes and exhibit reduction and oxidation at - 107 mV and +641 mV, with lowered reductive potentials. The synthesized quantum dot are suitable for low energy requiring electrochemical applications such as biological sensors and candidates for further investigation as photoluminescent biological labels.