Browsing by Author "Jijana, Abongile Nwabisa"

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    Development of electrochemical ZnSe Quantam dots biosensors for low-level detection of 17β-Estradiol estrogenic endocrine disrupting compound
    (University of the Western Cape, 2010) Jijana, Abongile Nwabisa; Iwuoha, Emmanuel; Dept. of Chemistry; Faculty of Science
    The main thesis hub was on development of two electrochemical biosensors for the determination of 17β-estradiol-estradiol: an estrogenic endocrine disrupting compound. Endocronology have significantly shown that the endocrine disruptors contribute tremendously to health problems encountered by living species today, problems such as breast cancer, reproductive abnormalities, a decline in male population most significant to aquatic vertebrates, reduced fertility and other infinite abnormalities recurring in the reproductive system of mostly male species. The first biosensor developed for the detection of 17β-estradiol-estradiol endocrine disrupting compound; consisted of an electro-active polymeric 3-mercaptoprorionic acid capped zinc selenide quantum dots cross linked to horseradish peroxidase (HRP) enzyme as a bio-recognition element. The second biosensor developed was comprised of cysteamine self assembled to gold electrode, with 3-mercaptopropionic acid capped zinc selenide quantum dots cross linked to cytochrome P450-3A4 (CYP3A4) enzyme in the presence of 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride and succinimide.
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    Polyaniline entrapped water-dispersible 3mpa-znse quantum dots and their application for the development of an enzymatic electrochemical nanobiosensor for the detection of 17β-estradiol, an endocrine-disrupting compound
    (SpringerLink, 2023) Jijana, Abongile Nwabisa
    17β-estradiol is used as a growth and fertility stimulant in the agronomic sector to induce fertility and manipulate reproductive characteristics in animals. However, unintended or unregulated distribution and exposure to even significant low levels of 17β-estradiol estrogen have detrimental health implication that can lead to reproductive abnormalities and even cancer. This could have severe effect on the ecosystem imbalance, food safety, to such a degree that its health impact necessitates rapid methods to probe for its prevalence and occurrence in the environment. Herein a simple, robust, sensitive and once-off use electrochemical biosensor to detect 17β-estradiol is developed, using 3-mercaptopropionic acid capped zinc selenide quantum dots trapped within the polyaniline (PANI) framework structure. The biosensor’s interaction with the substrate was based on the capability of the hemeprotein, horseradish peroxidase (HRP) enzyme (i.e., baroreceptor) to alternatively catalyze phenolic alcohols. The biosensor displayed a significantly low limit of detection limit (LOD) of value 0.2 × 10−6 M towards 17β-estradiol. The Mechaelis-Menten constant (Km) with the magnitude of 0.64 × 10−6 M was obtained; this indicates an outstanding affinity of the biosensing films towards 17β-estradiol. Subsequently, the developed biosensor was able to accurately and efficiently measure successive concentrations of 17β-estradiol from 0.2 × 10 to 4 × 10−6 M. The fabricated biosensor showed good selectivity towards 17β-estradiol compared to the other estrogenic endocrine-disrupting compounds such as estrone (E1), ethnylstradiol (EE2), and estriol (E3). The biosensor was capable of detecting 17β-estradiol in spiked tap water samples with good recoveries, thus affirming its potential to be applied for real electro-analysis of 17β-estradiol in treated wastewater.
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    Quantum dot sensitized estrogen receptor alpha-recombinant protein electrochemical biosensor for 17-beta estradiol
    (University of the Western Cape, 2016) Jijana, Abongile Nwabisa; Iwuoha, Emmanuel; Baker, Priscilla G.L.
    Estrogens play an extraordinary role in the endocrine system regulation through the stimulation and regulation of endocrine pathways. 17β-estradiol is one of the final metabolites in estrogen regulation by hydroxylase enzymes that are well recognized for their metabolic role in hormone fragmentation and dissociation, through hydroxylation reactions that reversibly convert a series of androgens to estrogens (i.e. or one estrogen to the other). However, the 17β-estradiol hormone has been classified as one of the estrogenic endocrine disrupting compounds {i.e. EDC (s)} that show significant adverse effects in the estrogen pathways of male and female animal species. Estrogen receptor alpha (ER-α) is significantly activated by 17β-estradiol, which is a steroid hormone. A biosensor system for the determination of 17β-estradiol was developed based on the highly selective and specific physiological substrate level activation of the ER-α biomolecule by the (17β-estradiol) compound. The chemically-tuned tin selenide quantum dots capped with 3-mercaptopropionic acid were produced at room temperature and employed to capture the ER-α micro-molecule onto the electrode surfaces. These quantum dots possessed average particle size (APS) diameters between 4.6 ± 0.6 nm and an indirect band gap energy (Eg) of 3.14 eV. Surface modification on the quantum dots permitted the formation of efficient amide bonds between the capping molecules of the quantum dots and the estrogen receptor-alpha. The tin selenide quantum dots platform enhanced the surface bio-reactivity of the receptorsensor film. The receptorsensor’s sensitivity towards 17β-estradiol was 5.9 μA/μM associated with a response time (tResponse) of less than 1.2 s. The formal potential, Ep˚ˈ, of the receptorsensor-substrate complex was 149 mV. A detection limit (DL) of 1.9 nM was obtained for the electrochemical biosensing methodology. 17β-estradiol–receptorsensor response kinetics were also evaluated, where a dissociation rate (kd) of 7.6 μM/s, a 50 % inhibition concentration (IC50) value of 3.4 nM and a binding efficiency (Bmax) of 7 nM were obtained. Effective measure of 17β-estradiol concentrations as low as 3.8 nM present in surface waters have been reported to induce feminisation in male aquatic species. The receptorsensor’s dynamic linear range (DLR) nevertheless showed capability of screening a minimum of 0.2 nM to a maximum of 8 nM of the 17β-estradiol concentrations. Furthermore, during the estrogen replacement therapy (ERT), 17β-estradiol concentration levels are monitored at frequent phases, wherein 17β-estradiol concentrations from as low as 0.37 nM are recovered in the serum (i.e. this value was also evaluated to be within the receptorsensor’s-DLR), determining its future capability to be developed for; clinical-diagnosis screening of the 17β-estradiol.