Browsing by Author "Baker, Priscilla G.L."
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Item Composite poly(dimethoxyaniline) electrochemical nanobiosensor for glufosinate and glyphosate herbicides(University of the Western Cape, 2008) Songa, Everlyne Apiyo; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of ScienceIn this thesis, I present a simple, sensitive and low cost electrochemical nanobiosensor for quantitative determination of the herbicides glufosinate, glyphosate and its metabolite aminomethylphosphonic acid (AMPA). Firstly, the nanostructured poly(2,5-dimethoxyaniline) (PDMA) materials were synthesized on gold electrode by the electrochemical "template"method using poly(4-styrenesulfonic acid) (PSS) as the dopant and structure-directing molecule. Fourier transform infrared (FTIR) spectroscopy, UV-Vis Spectroscopy, Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) studies inferred successful doping of the nanostructured PDMA film by PSS and that the template PSS directed the synthesis of both nanotubes and nanoparticles of PDMA with diameters less than 100 nm.Item Cytochrome C biosensor for the determination of trace level arsenic and cyanide compounds(University of the Western Cape, 2011) Fuku, Xolile Godfrey; Baker, Priscilla G.L.; Iwuoha, Emmanuel; Dept. of Chemistry; Faculty of ScienceIn this work, an electrochemical method based on a cyt c biosensor has been developed, for the detection of selected arsenic and cyanide compounds. Boron Doped Diamond (BDD) electrode was used as a transducer, onto which cyt c was immobilised and used for direct determination of Prussian blue, potassium cyanide and arsenic trioxide by inhibition mechanism. The sensitivity as calculated from cyclic voltammetry (CV) and square wave voltammetry (SWV), for each analyte in phosphate buffer (pH= 7) was found to be (1.087- 4.488 ×10-9 M) and the detection limits ranging from 0.0043- 9.1 μM. These values represent a big improvement over the current Environmental Protection Agency (EPA) and World Health Organisation (WHO) guidelines.Item Development of electrochemical sensors containing bimerallic silver and gold nanoparticles(University of the Western Cape, 2010) Mailu, Stephen Nzioki; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of SciencePolyaromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants that have been shown to be teratogenic, mutagenic and carcinogenic and pose serious threats to the health of aquatic and human life. Several methods have been developed for their determination such as immunoassay, gas chromatography and high performance liquid chromatography (HPLC) in combination with fluorescence or absorbance detection. However, these methods are known to manifest underlying disadvantages such as complicated pretreatment, high costs and time consuming processes. In this work, a simple, less time consuming electrochemical method in the form of an electrochemical sensor has been developed for the detection of PAHs. The sensor was fabricated by the deposition of silver-gold (1:3) alloy nanoparticles (Ag-AuNPs) on ultrathin overoxidized polypyrrole (PPyox) film which formed a PPyox/Ag-AuNPs composite on glassy carbon electrode (PPyox/Ag-AuNPs/GCE). The silver-gold alloy nanoparticles deposited to form the composite were chemically prepared by simultaneous reduction of silver nitrate (AgNO3) and chloroauric acid (HAuCl4) using sodium citrate and characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the alloy nanoparticles. Transmission electron microscopy showed that the synthesized nanoparticles were in the range of 20-50 nm. The properties of the composite formed upon deposition of the nanoparticles on the PPyox film were investigated by electrochemical methods. The PPyox/Ag-AuNPs/GCE sensor showed strong catalytic activity towards the oxidation of anthracene, phenanthrene and pyrene, and was able to simultaneously detect anthracene and phenanthrene in a binary mixture of the two. The catalytic peak currents obtained from square wave voltammetry increased linearly with anthracene, phenanthrene and pyrene concentrations in the range of 3.0 x 10-6 to 3.56 x 10-4 M,3.3 x 10-5 to 2.83 x 10-4 M, 3.3 x 10-5 to 1.66 x 10-4 M and with detection limits of 0.169 μM, 1.59 μM and 2.70 μM, respectively. The PPyox/Ag-AuNPs/GCE sensor is simple, has antifouling properties and is less time consuming with a response time of 4 s.Item The development of l-phenylalanine biosensor using boron-doped diamond (bdd) electrode modified with poly aniline-polyvinyl sulphonate composite film(University of the Western Cape, 2010) Mangombo, Zelo; Baker, Priscilla G.L.The aim of this project was to develop a biosensor on a modified boron-doped diamond (BDD) platform in order to determine L-phenylalanine (L-Phe) levels in the aqueous media and real samples. A BDD electrode modified with polyaniline (PANI) film doped with polyvinyl sulphonate (PVS), containing in-situ deposited tyrosinase (Tyr) enzyme was studied with special emphasis on the detection of L-phenylalanine (L-Phe). The PANI-PVS film was electrochemically coated on the BDD surface by cyclic voltammetry (CV) at 50 mV s-1 (versus Ag/AgCI). An increase in current density with increasing number of cycles was an indication of the polymer growth. The morphologies of the composite films were characterized by scanning electron microscopy (SEM).Item Development of Schiff base electrochemical sensors for the evaluation of polycyclic aromatic hydrocarbons in aqueous medium(University of the Western Cape, 2017) Ward, Meryck; Baker, Priscilla G.L.; Aubert, Pierre-HenriA novel monomer (N,N'-Bis-(1H-pyrrol-2-ylmethylene)-benzene-1,2-diamine-BPPD) was derived from the condensation reaction between o-phenylenediamine and a pyrrole derivative. The monomer was polymerized electrochemically to produce the new polymer material - polymerized(N,N'-Bis-(1H-pyrrol-2-ylmethylene)-benzene-1,2-diamine) PBPPD. This novel polymer material was deposited at the surface of a screen-printed carbon electrode, as a thin film, in the development of chemical sensors for the detection of polycyclic aromatic hydrocarbons (PAHs). The monomer material was characterized in terms of its optical (spectroscopy) and thermal properties. The polymer material was characterized in terms of its surface morphology and its redox electrochemistry. Fourier transform infrared spectroscopy (FTIR) was used to confirm the azomethine bond formation during the condensation reaction of an aldehyde and primary amine derivative.Item Electrochemical characterization of nanostructured SnO2 and TiO2 for potential application as dielectric materials in sulfonated-polyaniline based supercapacitors(University of the Western Cape, 2010) Ngqongwa, Lundi Vincent; Iwuoha, Emmanuel; Waryo, Tesfaye T.; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of ScienceIn this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).Item Electrochemical determination of phenothrin in fruit juices at graphene oxide-polypyrrole modified glassy carbon electrode(Elsevier, 2018) Tefera, Molla; Tessema, Merid; Admassie, Shimelis; Iwuoha, Emmanuel I.; Waryo, Tesfaye T.; Baker, Priscilla G.L.An electrochemical sensor was developed based on graphen oxide-polypyrrole modified glassy carbon electrode (GO/PPy/GCE) for sensitive determination of phenothrin in fruit samples. GO/PPy/GCE was characterized by scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR), Ultraviolet-Visible spectroscopy (UV–Vis) and Raman spectroscopy. The sensor was also characterized using electrochemical impedance spectroscopy and cyclic voltammetry. Compared to bare GCE, GO/GCE and PPy/GCE, the reduction peak current of phenothrin increased significantly at GO/PPy/GCE, demonstrating that GO/PPy/GCE exhibited electrocatalytic activity towards the reduction of phenothrin. Under the optimal conditions, the sensor showed a linear relationship over the range of 2.5×10−8-2.0×10−5 M with detection limits of 13.8×10−9 M. In addition, the analytical application of the proposed method was carried out by the determination of phenothrin in fruit juice samples.Item Electrolytic determination of phthalates organic pollutants with n nostructured titanium and iron oxides sensors(University of the Western Cape, 2010) Matinise, Nolubabalo; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of ScienceThis work reports the chemical synthesis, characterisation and electrochemical application of titanium dioxide (TiO2) and iron oxide (Fe2O3) nanoparticles in the determination of phthalates. The other part of this work involved electrochemical polymerization of aniline doped with titanium and iron oxide nanoparticles for the sensor platform in the electrolytic determination of phthalates. The TiO2 and Fe2O3 nanoparticles were prepared by sol gel and hydrothermal methods respectively. Particle sizes of 20 nm (TiO2) and 50 nm (Fe2O3) were estimated from transmission electron microscopy (TEM) The other technical methods used in this study for the characterization of the TiO2 and iron oxide Fe2O3 NPs were SEM, XRD and UV- visible spectroscopy. Cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties of the nanoparticles. These electrochemical studies of the nanoparticles were performed with a Fe2O3 or TiO2/nafion/glassy carbon membrane electrode in 0.1 M phosphate buffer (pH 7.0) and 0.1 M lithium perchlorate (pH 6.8) under an aerobic condition.Item Nanoparticulate of silver-modified poly (8-anilino-1-naphthalene sulphonic acid) nanobiosensor systems for the determination of Tuberculosis treatment drugs(University of the Western Cape, 2011) Ngece, Rachel Fanelwa; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of ScienceThis study firstly reports the development and characterization of PVP-AgNPs, PANSA and PVPAgNPs/ PANSA nanocomposite on gold. AFM and TEM analyses revealed highly electroactive nanocomposites whose morphogy and properties were essential for the immobilization of CYP2E1. Secondly, the development and characterization of Au/PVPAgNPs/ PANSA/CYP2E1, Au/PVP-AgNPs/PANSA/SA-CYP2E1 and Au/PVPAgNPs/ PANSA/EG-CYP2E1 nanobiosensors are reported. AFM studies displayed globular morphologies with large roughness for the enzyme modified electrodes as opposed to those electrodes without enzymes. Finally, the biotransformation of standard solutions of TB drugs (isoniazid, ethambutol, pyrazinamide and rifampicin) in pH 7.4, 0.1 M phosphate buffer solution is reported. The biotransformations of the TB drugs were successfully studied using cyclic voltammetry (CV), square wave voltammetry (SWV), differential voltammetry (DPV) and steady state amperometry under aerobic conditions. Very good detection limits were obtained for the standard solutions of TB drugs and were found to be in the micromolar range. The detection limit values for the individual TB drugs were 0.55 μM (isoniazid), 0.7 μM (ethambutol), 0.054 μM (pyrazinamide) and 0.05 μM (rifampicin). The detection limit results showed that the nanobiosensors were more sensitive and suitable for the determination of the respective drugs in plasma and serum.Item Nanostructured polyamic acid electrocatalysts for reliable analytical reporting of sulphonamides as contaminants of emerging concern(University of the Western Cape, 2019) Hamnca, Siyabulela; Baker, Priscilla G.L.; Chamier, JessicaPolyamic acid (PAA) nanostructured materials were successfully produced by electrochemical deposition and electrospinning using polyvinlypyrrolidone (PVP) as supporting polymer. Polyamic acid thin film and nanofibers were deposited directly at the surface of a screen-printed carbon electrode (SPCE) as electro-catalysts for reliable analytical reporting of sulphonamide as contaminants of emerging concern by electrochemical techniques. Fourier transform infrared (FTIR) spectroscopy was used to confirm the structural integrity of the PAA electrospun nanofibers compared to the chemical synthesized PAA. Brunauer-Emmett-Teller (BET) was used to determine the surface area of the nanofibers. The surface morphology and surface thickness of the polyamic acid (PAA) nanofibers on the screen-printed electrodes was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Cyclic voltammetry (CV) was used to study redox behavior of the nanostructured PAA modified screen-printed carbon electrodes. Electrochemical parameters surface concentration, diffusion coefficient, formal potential and peak separation were determined. Three sulphonamides were selected based on the United States of protection agency (US EPA) and World Health Organization (WHO) list of emerging contaminants and detected sulphonamides in environmental waters in South Africa and other African regions. The selected sulfonamides were evaluated at the unmodified and modified screen-printed carbon electrodes. The sulphonamides were evaluated in three different supporting electrolytes at pH < 7 and >7 to enhance electrochemical signal reporting. Sulfadiazine (SDZ), sulfamethoxazole (SMX) and sulfamethazine (SMZ) displayed peaks at 0.80 V vs Ag/AgCl in 0.1 M tris-HCl using square wave voltammetry at the unmodified transducer. At the PAA thin film transducer, SDZ, SMX and SMZ displayed well-defined analytical oxidative peaks at 0.77 V 0.82 V and 0.83 V vs Ag/AgCl respectively. The LOD (n=3) for SDZ was found to be 12.14 ųM with a correlation coefficient of 0.9950. The LOD (n=3) for SMX and SMZ was found to 14.59 ųM (R2 =0.9928) and 10.41 ųM (R2 =0.9963). These sulphonamides were also electro-analytical evaluated at the screen-printed carbon PAA nanofiber modified transducer. SDZ, SMX and SMZ produced well-defined analytical signals at 0.79 V, 0.81 V and 0.78 V vs Ag/AgCl respectively. The determined LOD (n=3) for the individual sulphonamides was 8.26 ųM, 16.59 ųM and 8.81 ųM SDZ, SMX and SMZ respectively. The linearity correlation coefficient (R2) was determined to be 0.9977, 0.9956 and 0.9974 respectively. The efficacy of the proposed nanostructured PAA thin film modified screen-printed carbon sensor was evaluated by performing recovery studies for the selected sulphonamides using square wave voltammetry. Tap water was used to simulate environmental matrix. The recoveries of SDZ with respect to each concentration were 98.84% (RSD 4.98%) to 40.58% (RSD 6.74%). For SMX the recoveries were 154.17% (RSD 11.00%) to 111.03% (RSD 16.80%). The recoveries for SMZ with respect to each concentration were 184% (RSD 8.19%) to 90.26 (RSD 18.26%) indicating the reliability of the analytical results.Item Polyamic acid composites for multiiple sensing applications in complex sample matrices(2013) Hess, Euòdia Hallouise; Baker, Priscilla G.L.; Iwuoha, EmmanuelPolyamic acid-polypyrrole (PAA/PPy) composite films were prepared and characterised for the use as conducting platforms in the design of biosensor systems. The thin films were synthesised by electrochemical method from a solution containing controlled molar ratio of chemically synthesised polyamic acid (PAA) and pyrrole monomer. Homogenous films were obtained incorporating PAA into electropolymerised polypyrrole (PPy) thin film. The concentration of PAA (1.37 × 10-6 M) was kept fixed throughout the composite ratio analysis, whilst the concentration of PPy was varied from 1.9 × 10-3 M to 9.9 × 10-3 M. The PAA/PPy thin films were electrodeposited at a glassy carbon electrode (GCE) and characterised using Fourier Transform Infrared Spectroscopy (FTIR), Raman spectroscopy, Atomic Force microscopy (AFM), Scanning electron microscopy (SEM) and electrochemical (CV, SWV) techniques. The composition that best represented the homogenous incorporation of PAA into PPy matrix was observed at a PAA/PPy ratio of 1: 4.13 × 10-3. This composite was observed to have two sets of coupled peaks with formal potential 99 mV and 567 mV respectively. The De determined from cyclic voltammetry using the anodic peak currents were found to be twice as high (5.82 × 10-4 cm2/s) as the De calculated using the cathodic peak currents (2.60 × 10-4 cm2/s), indicating that the composite favours anodic electron mobility. Surface morphology and spectroscopy data support the formation of a homogenous polymer blend at the synthesis ratio represented by composite 3. For the construction of a biosensor the spectroscopic and electrochemical properties of the enzyme, luciferase and the analytes i.e naphthalene and fluoranthene were evaluated. Fluorescence spectroscopy studies were carried out to characterize the enzyme’s bioluminescence response in PBS at pH 7. Luciferase showed an absorption peak at 340 nm. The bioluminescence properties of the enzyme with the analytes were explored by fluorescence spectroscopy. The emmision peak at 340 nm gradually decreased as the concentration of each analyte was increased respectively.Item 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.Item Sensitive electrochemical determination of ethambutol in pharmaceutical formulation and human urine at nickel nanoparticles/electrochemically reduced graphene oxide modified electrode(Chemical Society of Ethiopia, 2019) Mekassa, Birhanu; Baker, Priscilla G.L.; Chandravanshi, Bhagwan Singh; Tessema, MeridThis paper describes the application of nickel nanoparticles decorated electrochemically reduced graphene oxide modified glassy carbon electrode (NiNPs/ERGO/GCE) for the determination of ethambutol (ETB), an anti-Mycobacterium tuberculosis drug. The modified electrode showed remarkable electrocatalytic properties accompanied with a significant enhancement in the peak current response towards ETB compared to the bare electrode. The results showed that the composite modified electrode played a significant catalytic role due to the synergetic effect of NiNPs and ERGO. The NiNPs/ERGO modified electrode demonstrated excellent square wave voltammetric response towards ETB determination at the NiNPs/ERGO/GCE in the range 0.05‒100 μM. The sensor demonstrated outstanding sensitivity towards ETB determination with limit of detection (LOD) and limit of quantification (LOQ) of 0.023 and 0.075 μM, respectively. The developed sensor was effectively validated for real sample study using drug formulation and urine samples which showed an acceptable recovery (99.6‒109%). The electrode also exhibited good precision (RSD < 1%, n = 20), reproducibility (RSD < 1.9%, n = 3), long-term stability (92% of its initial response after two weeks) and selectivity towards interfering substances in the determination of ethambutol.Item Synthesis and electrochemical modulation of the actuator properties of poly(phenazine-2,3-diimino (pyrrol-2-yl))(University of the Western Cape, 2008) Botha, Shanielle Veronique; Iwuoha, Emmanuel; Baker, Priscilla G.L.; Dept. of Chemistry; Faculty of ScienceThe focus of this study is to synthesize a novel hinged polymer actuator. The linking molecule (hinge) is phenazine with interconnected dipyrrole units.