An electrochemical urea biosensor on a carbon nanofiber-poly (amidoamine) dendrimer supramolecular-platform
- Authors: Blessie, Wessel
- Date: 2020
- Subjects: Supramolecular electrochemistry , Nanomedicine , Polymeric composites , Carbon composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/473889 , uj:42696
- Description: Abstract: The concentration of urea in serum or urine in human body should be in moderate levels (3.3–6.7 mM). The elevation of urea above the normal level indicates gastrointestinal bleeding, obstruction of the urinary tract, burns, shock, or renal failure. The decline in the concentration of urea below moderate levels causes cachexia, hepatic failure, and nephritic syndrome. The increase/decrease in the concentration of urea poses health risks. Thus, it is essential to determine the urea concentration for early diagnosis of kidney related disease. In this mini-dissertation, we report a novel amperometric urea biosensor based on the immobilisation of urease enzyme on carbon nanofiber-generation 3 polyamidoamine dendrimer immobilisation layer on a glassy carbon electrode (GCE). Electrospun polyacrylonitrile (PAN) based carbon nanofibers were obtained with an average diameter of 132 nm through stabilization, electrospinning, and carbonization of polyacrylonitrile (PAN) polymer. The structure and the morphology of the PAN carbon nanofibers were studied by High Resolution Transmission Electron Microscope (HR-TEM) and Field Emission Scanning Electron Microscope (FE-SEM)... , M.Sc. (Nanoscience)
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- Authors: Blessie, Wessel
- Date: 2020
- Subjects: Supramolecular electrochemistry , Nanomedicine , Polymeric composites , Carbon composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/473889 , uj:42696
- Description: Abstract: The concentration of urea in serum or urine in human body should be in moderate levels (3.3–6.7 mM). The elevation of urea above the normal level indicates gastrointestinal bleeding, obstruction of the urinary tract, burns, shock, or renal failure. The decline in the concentration of urea below moderate levels causes cachexia, hepatic failure, and nephritic syndrome. The increase/decrease in the concentration of urea poses health risks. Thus, it is essential to determine the urea concentration for early diagnosis of kidney related disease. In this mini-dissertation, we report a novel amperometric urea biosensor based on the immobilisation of urease enzyme on carbon nanofiber-generation 3 polyamidoamine dendrimer immobilisation layer on a glassy carbon electrode (GCE). Electrospun polyacrylonitrile (PAN) based carbon nanofibers were obtained with an average diameter of 132 nm through stabilization, electrospinning, and carbonization of polyacrylonitrile (PAN) polymer. The structure and the morphology of the PAN carbon nanofibers were studied by High Resolution Transmission Electron Microscope (HR-TEM) and Field Emission Scanning Electron Microscope (FE-SEM)... , M.Sc. (Nanoscience)
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Electrochemical detection of arsenic and selenium on modified carbon based nanocomposite electrodes
- Authors: Idris, Azeez Olayiwola
- Date: 2016
- Subjects: Nanostructured materials , Electrodes, Carbon , Electrochemical analysis , Organic water pollutants , Carbon composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/124946 , uj:20978
- Description: Abstract: This study explores the applications of nanomaterial modified on glassy carbon electrode (GCE) in the electroanalysis of arsenic and selenium ions in water. GCE was modified with gold nanoparticles and reduced graphene oxide. Gold nanoparticle (AuNPs) modified GCE (GCE-AuNPs) was prepared by electrochemical deposition of gold from 5 mM of HAuCl4 solutions by cycling the potential from -400 mV to 1100 mV for 10 cycles at a scan rate of 50 mVs-1. GCEAuNPs was electrochemically investigated using redox probes which are [Fe (CN) 6]3-/4- and Ru (NH3)62+/3+. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical determination of selenium by square wave anodic stripping voltammetry (SWASV) using GCE-AuNPs was carried out under the optimised conditions: pH 1, deposition potential of -100 mV, deposition time of 60 s and 0.1 M H2SO4 as supporting electrolyte. A detection limit of 0.64 μg L-1 was obtained. Cu and Cd were the only significant interferences observed for the electrochemical detection of selenium. Attempt was also made to sense selenium in tap water, concentration of 8.86 (± 0.34) ppb Se, was calculated for the tap water. The electrochemical method was validated with ICP-OES. Furthermore, arsenic was detected on GCE-AuNPs by SWASV. The sensing of arsenic was also optimised at different analytical conditions and a detection limit of 0.75 μgL-1 was obtained. Cu, Cd and Hg were the major interferences in arsenic sensing. Ammonia, EDTA and G3 PPI were used as ligands to mask the interference effect of copper on arsenic sensing in the bid to remove interference. Graphene oxide was synthesised by using Hummer`s methods and was further reduced to reduced graphene oxide using ascorbic acid. The reduced graphene oxide was used to modify GCE, the modification of GCE with rGO-GCE resulted in an increase in the electroactive surface area of the electrode which led to enhance the redox peak of [Fe(CN)6]3-/4- in comparison to the bare GCE. SWASV was used to detect Se (IV) in water at the following optimum conditions: 0.1 M HNO3 as supporting electrolyte, deposition potential of -100 mV and pre-concentration time of 240 s. The rGO-GCE sensor was able to detect Se (IV) to the limit of 2.2 ppb and was not susceptible to many interfering cations except Cu (II) and Cd (II). , M.Sc. (Chemistry)
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- Authors: Idris, Azeez Olayiwola
- Date: 2016
- Subjects: Nanostructured materials , Electrodes, Carbon , Electrochemical analysis , Organic water pollutants , Carbon composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/124946 , uj:20978
- Description: Abstract: This study explores the applications of nanomaterial modified on glassy carbon electrode (GCE) in the electroanalysis of arsenic and selenium ions in water. GCE was modified with gold nanoparticles and reduced graphene oxide. Gold nanoparticle (AuNPs) modified GCE (GCE-AuNPs) was prepared by electrochemical deposition of gold from 5 mM of HAuCl4 solutions by cycling the potential from -400 mV to 1100 mV for 10 cycles at a scan rate of 50 mVs-1. GCEAuNPs was electrochemically investigated using redox probes which are [Fe (CN) 6]3-/4- and Ru (NH3)62+/3+. The current and the reversibility of the redox probes were enhanced in the presence of modifiers. The electrochemical determination of selenium by square wave anodic stripping voltammetry (SWASV) using GCE-AuNPs was carried out under the optimised conditions: pH 1, deposition potential of -100 mV, deposition time of 60 s and 0.1 M H2SO4 as supporting electrolyte. A detection limit of 0.64 μg L-1 was obtained. Cu and Cd were the only significant interferences observed for the electrochemical detection of selenium. Attempt was also made to sense selenium in tap water, concentration of 8.86 (± 0.34) ppb Se, was calculated for the tap water. The electrochemical method was validated with ICP-OES. Furthermore, arsenic was detected on GCE-AuNPs by SWASV. The sensing of arsenic was also optimised at different analytical conditions and a detection limit of 0.75 μgL-1 was obtained. Cu, Cd and Hg were the major interferences in arsenic sensing. Ammonia, EDTA and G3 PPI were used as ligands to mask the interference effect of copper on arsenic sensing in the bid to remove interference. Graphene oxide was synthesised by using Hummer`s methods and was further reduced to reduced graphene oxide using ascorbic acid. The reduced graphene oxide was used to modify GCE, the modification of GCE with rGO-GCE resulted in an increase in the electroactive surface area of the electrode which led to enhance the redox peak of [Fe(CN)6]3-/4- in comparison to the bare GCE. SWASV was used to detect Se (IV) in water at the following optimum conditions: 0.1 M HNO3 as supporting electrolyte, deposition potential of -100 mV and pre-concentration time of 240 s. The rGO-GCE sensor was able to detect Se (IV) to the limit of 2.2 ppb and was not susceptible to many interfering cations except Cu (II) and Cd (II). , M.Sc. (Chemistry)
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Synthesis and characterization of polymer and carbonaceous nanocomposites and their application in hydrostatic pressure sensing
- Authors: Mofokeng, Lethula Excellent
- Date: 2017
- Subjects: Carbon composites , Nanocomposites (Materials) , Nanostructured materials , Polymeric composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/244052 , uj:25235
- Description: M.Sc. (Nanoscience) , Abstract: Flexible polymer nanocomposites thin films holds promising applications in electronics and are good candidates for pressure sensing and other technological applications due to their flexibility and other novel properties they exhibits. Carbonaceous nanomaterial polymer nanocomposites were utilized to fabricate pressure sensors via a simple and cost- effective process of non-covalent functionalization. We successfully managed to demonstrate the use of cheap, stable, thermoplastic polymers for producing thin films for pressure sensing applications and applicable also for future electronic devices applications. The use of CNPs gave better resistive and capacitive sensing application with response times ranging from 3 to 11 seconds and operate effective for a wide dynamic range (56 to 190 kPa) for both resistive and capacitive sensing compared to O-MWCNTs. The sensitivities of carbonaceous nanomaterials are dependent on the nature of the polymer, loadings of polymer ratios (1:1, 1:2, 1:3, 2:1, 2:2, 2:3, 3:1, 3:2 and 3:3) and percolation threshold. CNPs/PAN pressure sensor was measured for electrical resistance and capacitance pressure sensing. The CNPs/PAN was the highest sensitivity resistive pressure sensor than any other in relation to O-MWCNTs and rGO – based pressure sensors having 5.12 kPa-1. CNPs/PAN took three second to reach 90% pressure stimuli response time and also it took in three seconds for 90 % recovery time to retain its initial state at Ro under applied pressure with linear range from 56 to 190 kPa. Capacitive sensitivity was 1.33 kPa-1 for CNPs and CA thin film pressure sensor exhibiting linearity with a wide dynamic range and reversible behaviour. When Fe3O4 was incorporated to CNPs and CA, low sensitivities for resistive and capacitive pressure sensing were obtained for CNPs/Fe3O4/CA. Resistive sensitivity was 2.08 x 10-6 kPa-1 and 0.04 kPa-1 for capacitive sensitivities. This implies that, Fe3O4 had a huge impact on the structure, arrangement, uniformity, distribution and conducting channels within the polymer nanocomposites. As for O-MWCNTs and rGO –based pressure sensors, similar reduction in sensitivities due to Fe3O4...
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- Authors: Mofokeng, Lethula Excellent
- Date: 2017
- Subjects: Carbon composites , Nanocomposites (Materials) , Nanostructured materials , Polymeric composites
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/244052 , uj:25235
- Description: M.Sc. (Nanoscience) , Abstract: Flexible polymer nanocomposites thin films holds promising applications in electronics and are good candidates for pressure sensing and other technological applications due to their flexibility and other novel properties they exhibits. Carbonaceous nanomaterial polymer nanocomposites were utilized to fabricate pressure sensors via a simple and cost- effective process of non-covalent functionalization. We successfully managed to demonstrate the use of cheap, stable, thermoplastic polymers for producing thin films for pressure sensing applications and applicable also for future electronic devices applications. The use of CNPs gave better resistive and capacitive sensing application with response times ranging from 3 to 11 seconds and operate effective for a wide dynamic range (56 to 190 kPa) for both resistive and capacitive sensing compared to O-MWCNTs. The sensitivities of carbonaceous nanomaterials are dependent on the nature of the polymer, loadings of polymer ratios (1:1, 1:2, 1:3, 2:1, 2:2, 2:3, 3:1, 3:2 and 3:3) and percolation threshold. CNPs/PAN pressure sensor was measured for electrical resistance and capacitance pressure sensing. The CNPs/PAN was the highest sensitivity resistive pressure sensor than any other in relation to O-MWCNTs and rGO – based pressure sensors having 5.12 kPa-1. CNPs/PAN took three second to reach 90% pressure stimuli response time and also it took in three seconds for 90 % recovery time to retain its initial state at Ro under applied pressure with linear range from 56 to 190 kPa. Capacitive sensitivity was 1.33 kPa-1 for CNPs and CA thin film pressure sensor exhibiting linearity with a wide dynamic range and reversible behaviour. When Fe3O4 was incorporated to CNPs and CA, low sensitivities for resistive and capacitive pressure sensing were obtained for CNPs/Fe3O4/CA. Resistive sensitivity was 2.08 x 10-6 kPa-1 and 0.04 kPa-1 for capacitive sensitivities. This implies that, Fe3O4 had a huge impact on the structure, arrangement, uniformity, distribution and conducting channels within the polymer nanocomposites. As for O-MWCNTs and rGO –based pressure sensors, similar reduction in sensitivities due to Fe3O4...
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