Collective human biological signal-based identification and authentication in access control environments
- Van der Haar, Dustin Terence
- Authors: Van der Haar, Dustin Terence
- Date: 2014-10-13
- Subjects: Computers - Access control , Biometric identification , Biosensors
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/364585 , uj:12604 , http://hdl.handle.net/10210/12392
- Description: Ph.D. (Computer Science) , The introduction of new portable sensors that monitor physiological systems in the human body has allowed quality of life and medical diagnostic applications to be taken directly to the user, without the constraints of physical space or inconvenience. The potential of these sensors in the domain of authentication and identi cation is becoming more feasible each day and current research in these biometric systems show a great deal of promise. Novel biometric systems are being introduced that use biological signals (also known as biosignals) in the human body captured by these sensors (such as brain waves or heart rate) as the core unique attribute. The study builds on the proliferation of these sensors and proposes an interoperable model called CoBI, which allows individual or multi-factor authentication and identi cation to take place. The model provides a platform for any viable biosignal that can be used for the purposes of identi cation and authentication, by providing pluggable sensor and signal processing components. These components can then convert biosignals into a common format, a feature vector consisting of estimated autoregressive (AR) coe cients. Once they are in a common format they can then be merged together to form a consolidated feature vector using feature fusion. This consolidated feature vector can then be persisted during enrolment or passed further for matching using classi cation techniques, such as K-Nearest Neighbour. The results, from the comprehensive benchmark performed (called BAMBI) on an implemented version of the model (called CaNViS), have shown that biological signals that contain cardiac and neurological components (ie. from an electrocardiogram (ECG) and electroencephalogram (EEG), respectively) can be captured, processed, consolidated and classi ed using the CoBI model successfully. By utilising the correct AR model order during feature estimation for the cardiac and neurological components, along with the appropriate classi er for matching, the biometric system yields nominal results for authentication and identi cation in access control environments.
- Full Text:
- Authors: Van der Haar, Dustin Terence
- Date: 2014-10-13
- Subjects: Computers - Access control , Biometric identification , Biosensors
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/364585 , uj:12604 , http://hdl.handle.net/10210/12392
- Description: Ph.D. (Computer Science) , The introduction of new portable sensors that monitor physiological systems in the human body has allowed quality of life and medical diagnostic applications to be taken directly to the user, without the constraints of physical space or inconvenience. The potential of these sensors in the domain of authentication and identi cation is becoming more feasible each day and current research in these biometric systems show a great deal of promise. Novel biometric systems are being introduced that use biological signals (also known as biosignals) in the human body captured by these sensors (such as brain waves or heart rate) as the core unique attribute. The study builds on the proliferation of these sensors and proposes an interoperable model called CoBI, which allows individual or multi-factor authentication and identi cation to take place. The model provides a platform for any viable biosignal that can be used for the purposes of identi cation and authentication, by providing pluggable sensor and signal processing components. These components can then convert biosignals into a common format, a feature vector consisting of estimated autoregressive (AR) coe cients. Once they are in a common format they can then be merged together to form a consolidated feature vector using feature fusion. This consolidated feature vector can then be persisted during enrolment or passed further for matching using classi cation techniques, such as K-Nearest Neighbour. The results, from the comprehensive benchmark performed (called BAMBI) on an implemented version of the model (called CaNViS), have shown that biological signals that contain cardiac and neurological components (ie. from an electrocardiogram (ECG) and electroencephalogram (EEG), respectively) can be captured, processed, consolidated and classi ed using the CoBI model successfully. By utilising the correct AR model order during feature estimation for the cardiac and neurological components, along with the appropriate classi er for matching, the biometric system yields nominal results for authentication and identi cation in access control environments.
- Full Text:
Development of an electrochemical cholesterol biosensor based on poly (propylene imine) dendrimer- quantum dots nanocomposite
- Authors: Mokwebo, Kefilwe Vanessa
- Date: 2018
- Subjects: Electrochemical sensors , Biosensors , Quantum dots , Nanostructured materials , Dendrimers in medicine , Cholesterol - Physiological effect
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/279597 , uj:30029
- Description: M.Sc. (Nanoscience) , Abstract: One of the parameters that cause cardiovascular diseases (CVDs) is high level of cholesterol in the blood. Therefore, monitoring of cholesterol level is of great importance, especially to elderly people and people with high risk of such diseases. This work explores the applicability of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) in developing a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The as-synthesized mercaptopropionic acid (MPA) capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), powdered X-ray diffraction (XRD), fourier transform infrared (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima red-shifted as the reaction time and shell growth increased. The increase in PL intensities shows proper passivation of the QDs surface with PL quantum yield (PLQY) of 33.8 %, 69.2 % and 57 %, for CdTe, CdTe/CdSe and CdTe/CdSe/ZnSe QDs respectively. The XRD patterns of all the as-synthesized QDs consist of three diffraction peaks corresponding to (111), (220) and (311) cubic zinc blended structures. The estimated particle size of CdTe/CdSe/ZnSe QDs from XRD and TEM are 4.32 and 4.08 nm, respectively while the EDX confirmed the presence of corresponding elements. For biosensor design, PPI dendrimer was electrochemically deposited on glassy carbon electrode (GCE) and characterized using cyclic voltammetry (CV) and impedance spectroscopy (EIS) in both phosphate buffer solution (PBS) and ferricyanide solution ([Fe(CN)6]-3/-4) This was followed by drop-drying the QDs on the electrode to form GCE/PPI/QDs. Finally, cholesterol oxidase (ChOx) was drop-dried on the GCE/PPI/QDs electrode to produce GCE/PPI/QDs/ChOx-based electrochemical cholesterol biosensor. Scanning electron microscopy (SEM) was used to characterize screen printed carbon electrode (SPCE) as it was modified with different materials and was able to capture the nano-globular morphology of PPI dendrimer. The GCE/PPI/QDs/ChOx based cholesterol biosensor was able to detect cholesterol in the range 0.1-10 mM with a...
- Full Text:
- Authors: Mokwebo, Kefilwe Vanessa
- Date: 2018
- Subjects: Electrochemical sensors , Biosensors , Quantum dots , Nanostructured materials , Dendrimers in medicine , Cholesterol - Physiological effect
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/279597 , uj:30029
- Description: M.Sc. (Nanoscience) , Abstract: One of the parameters that cause cardiovascular diseases (CVDs) is high level of cholesterol in the blood. Therefore, monitoring of cholesterol level is of great importance, especially to elderly people and people with high risk of such diseases. This work explores the applicability of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) in developing a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The as-synthesized mercaptopropionic acid (MPA) capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), powdered X-ray diffraction (XRD), fourier transform infrared (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima red-shifted as the reaction time and shell growth increased. The increase in PL intensities shows proper passivation of the QDs surface with PL quantum yield (PLQY) of 33.8 %, 69.2 % and 57 %, for CdTe, CdTe/CdSe and CdTe/CdSe/ZnSe QDs respectively. The XRD patterns of all the as-synthesized QDs consist of three diffraction peaks corresponding to (111), (220) and (311) cubic zinc blended structures. The estimated particle size of CdTe/CdSe/ZnSe QDs from XRD and TEM are 4.32 and 4.08 nm, respectively while the EDX confirmed the presence of corresponding elements. For biosensor design, PPI dendrimer was electrochemically deposited on glassy carbon electrode (GCE) and characterized using cyclic voltammetry (CV) and impedance spectroscopy (EIS) in both phosphate buffer solution (PBS) and ferricyanide solution ([Fe(CN)6]-3/-4) This was followed by drop-drying the QDs on the electrode to form GCE/PPI/QDs. Finally, cholesterol oxidase (ChOx) was drop-dried on the GCE/PPI/QDs electrode to produce GCE/PPI/QDs/ChOx-based electrochemical cholesterol biosensor. Scanning electron microscopy (SEM) was used to characterize screen printed carbon electrode (SPCE) as it was modified with different materials and was able to capture the nano-globular morphology of PPI dendrimer. The GCE/PPI/QDs/ChOx based cholesterol biosensor was able to detect cholesterol in the range 0.1-10 mM with a...
- Full Text:
DNA hybridisation sensors for product authentication and tracing : state of the art and challenges
- Hlongwane, Gloria Ntombenhle, Dodoo-Arhin, David, Wamwangi, Daniel, Daramola, Michael Olawale, Moothi, Kapil, Iyuke, Sunny Esayegbemu
- Authors: Hlongwane, Gloria Ntombenhle , Dodoo-Arhin, David , Wamwangi, Daniel , Daramola, Michael Olawale , Moothi, Kapil , Iyuke, Sunny Esayegbemu
- Date: 2019
- Subjects: DNA hybridisation , Biosensors , Electrochemical detection
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/403766 , uj:33847 , Citation: Hlongwane, G.N. et al. 2019. DNA hybridisation sensors for product authentication and tracing : state of the art and challenges. South African Journal of Chemical Engineering 27 (2019) 16–34
- Description: Abstract: The wide use of biotechnology applications in bioprocesses such as the food and beverages industry, pharmaceuticals, and medical diagnostics has led to not only the invention of innovative products but also resulted in consumer and environmental concerns over the safety of biotechnology-derived products. Controlling and monitoring the quality and reliability of biotechnology-derived products is a challenge. Current tracking and tracing systems such as barcode labels and radio frequency identification systems track the location of products from primary manufactures and/or producers throughout globalised distribution channels. However, when it comes to product authentication and tracing, simply knowing the location of the product in the supply chain is not sufficient. DNA hybridisation sensors allows for a holistic approach into product authentication and tracing in that they enable the attribution of active ingredients in biotechnology-derived products to their source. In this article, the state-of-the-art of DNA hybridisation sensors, with a focus on the application of graphene as the backbone, for product authentication and tracing is reviewed. Candidate DNA biocompatible materials, properties and transduction schemes that enable detection of DNA are covered in the discussion. Limitations and challenges of the use of DNA biosensing technologies in real-life environmental, biomedical and industrial fields as opposed to clean-cut laboratory conditions are also enumerated. By considering experimental research versus reality, this article outlines and highlights research needed to overcome commercialisation barriers faced by DNA biosensing technologies. In addition, the content is thought-provoking to facilitate development of cutting edge research activities in the field.
- Full Text:
- Authors: Hlongwane, Gloria Ntombenhle , Dodoo-Arhin, David , Wamwangi, Daniel , Daramola, Michael Olawale , Moothi, Kapil , Iyuke, Sunny Esayegbemu
- Date: 2019
- Subjects: DNA hybridisation , Biosensors , Electrochemical detection
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/403766 , uj:33847 , Citation: Hlongwane, G.N. et al. 2019. DNA hybridisation sensors for product authentication and tracing : state of the art and challenges. South African Journal of Chemical Engineering 27 (2019) 16–34
- Description: Abstract: The wide use of biotechnology applications in bioprocesses such as the food and beverages industry, pharmaceuticals, and medical diagnostics has led to not only the invention of innovative products but also resulted in consumer and environmental concerns over the safety of biotechnology-derived products. Controlling and monitoring the quality and reliability of biotechnology-derived products is a challenge. Current tracking and tracing systems such as barcode labels and radio frequency identification systems track the location of products from primary manufactures and/or producers throughout globalised distribution channels. However, when it comes to product authentication and tracing, simply knowing the location of the product in the supply chain is not sufficient. DNA hybridisation sensors allows for a holistic approach into product authentication and tracing in that they enable the attribution of active ingredients in biotechnology-derived products to their source. In this article, the state-of-the-art of DNA hybridisation sensors, with a focus on the application of graphene as the backbone, for product authentication and tracing is reviewed. Candidate DNA biocompatible materials, properties and transduction schemes that enable detection of DNA are covered in the discussion. Limitations and challenges of the use of DNA biosensing technologies in real-life environmental, biomedical and industrial fields as opposed to clean-cut laboratory conditions are also enumerated. By considering experimental research versus reality, this article outlines and highlights research needed to overcome commercialisation barriers faced by DNA biosensing technologies. In addition, the content is thought-provoking to facilitate development of cutting edge research activities in the field.
- Full Text:
Fabrication and electrochemical characterization of highly efficient hierarchically assembled hybrid two-dimensional nanointerfaces for electrochemical biosensing and bioelectronics
- Authors: Kumari, Renu
- Date: 2018
- Subjects: Biosensors , Nanostructured materials , Bioelectrochemistry
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/401096 , uj:33504
- Description: Abstract : Two dimensional (2D) materials have provided a new era to biosensors research. Biosensors are functional biodevices which include the integration of biology with electronics. The integration of 2D materials with other nanomaterials has transformed the understanding of the biological and electronics world and has paved a way for the design and fabrication of novel 2D nanointerfaces. The use of 2D nanointerfaces has given great success to biosensors and bioelectronics field which ultimately impacts on biomedical diagnosis and sensing applications. The superior properties of 2D materials such as large surface area, ease of hybridization, good biocompatibility, and high electron transfer properties make them ideal interface materials for the design and fabrication of bioelectronic devices including biosensors. The thesis focused on the fabrication of 2D nanointerfaces by combining two 2D hybrid materials and then nanostructuring with metal nanoparticles for better electron transfer within the interface which is followed by immobilization of enzyme as a bio-recognition element for biosensing purposes. The conjugation of the 2D hybrid nanointerface materials was achieved through the self-assembly technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used in the study for characterization of the 2D hybrid nanointerface structures and chronoamperometry studies were employed to investigate the electrobiocatalytic properties of the 2D hybrid nanointerfaces structures. Structural characterization was done by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques for morphological details of 2D hybrid nanointerfaces structures. The fabrication of bioelectrodes was achieved by using the conjugated 2D hybrid nanointerface materials. ix There are three different segments in this research study. All of these different segments involved the use of 2D materials for bioelectronics purposes. The first phase involved the fabrication of smart hierarchically self-assembled 2D electrobiocatalytic interface system based on the combination of gold nanoparticles (AuNPs) doped graphene oxide (GO)-molybdenum disulfide (MoS2) layered nanohybrid, conjugated with poly (N-isopropylacrylamide, PNIPAAm) resulting in GO/AuNPs/MoS2/PNIPAAm interface. The introduction of PNIPAAm improved the stability of the self-assembled GO/AuNPs/MoS2 interface structure. Horseradish peroxidase (HRP) was subsequently immobilized on the GO/AuNPs/MoS2/PNIPAAm interface through electrostatic interactions giving GO/AuNPs/MoS2/PNIPAAm/Peroxidase electrobiocatalytic interface system as a platform for electrobiocatalysis reactions for biosensing applications. Morphological characterization of GO/AuNPs/MoS2/PNIPAAm indicates that this 2D nanointerface structure has a wide surface area for enzyme immobilization due to their flake-like structure. CV showed diffusion-controlled electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using hydrogen peroxide (H2O2) as a model analyte. The fabricated bioelectrode exhibits a wide linear response to the detection of H2O2 from 1.57 to 11.33 mM, with a detection limit of 3.34 mM (S/N=3) and a capacitance of 8.6 F/cm2. The second phase of the study involved the fabrication of hybrid dual 2D-nanohybrid structure through self-assembly combination AuNPs with hybrid 2D materials consisting of boron nitride (BN) and tungsten disulphide (WS2) as a nanointerface system for electrochemical biosensing. HRP was immobilized on the hybrid dual 2Dnanoparticle systems to form a biointerface. Structural characterization showed high crystallinity in the fabricated structure, while morphological characterization confirmed x the high surface to volume area of the hybrid material and the presence of welldispersed AuNPs. Electrochemical characterization also confirmed that the fabricated HRP/BN/WS2/AuNPs/GC bioelectrode exhibited excellent electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using H2O2 as a model analyte. The fabricated bioelectrode exhibited a wide linear range from 0.15 mM to 15.01 mM towards detection of H2O2 with a limit of detection of 3.0 mM (S/N = 3) and a sensitivity of 19.16 μA/mM/cm2. Theoretical studies of the BN/Au/WS2(001) nanohybrid structure was carried out using density functional theory (DFT) calculation for confirming the charge transport mobility and conductivity of the fabricated material. DFT calculations combined with the experimental studies showed that the self-assembled combination of the BN/Au/WS2(001) nanocomposite enhances the performance of the fabricated biosensor due to an introduced new electronic state emanating from the N 2p orbital. The third phase of the study involved the synthesis of acetylene sourced graphene (Gr) by chemical vapour deposition (CVD) method. Self-assembly method was used to prepare the 2D nanohybrid interfaces, which consist of Gr, WS2, AuNPs and HRP for fabricating electrochemical biosensor for detection of H2O2. The XRD results revealed that Gr/WS2/AuNPs nanohybrid structure has good crystalline nature. CV and electrochemical impedance spectroscopy results showed that due to the incorporation of AuNPs, the redox properties of Gr/WS2/AuNPs/HRP conjugate 2D hybrid structure improved in comparison to Gr/WS2/HRP. The same trend was observed in the chronoamperometric results. The Gr/WS2/AuNPs/HRP/GCE modified bioelectrode exhibited a good electrobiocatalytic performance towards the detection of H2O2 over a relatively wider linear range (0.40 mM to 23 mM), with a higher xi sensitivity (11.07 μA/mM/cm2) than that of Gr/WS2/HRP/GCE modified bioelectrode (9.23 μA/mM/cm2). The results have shown that electrobiocatalytic reactions can be controlled by modifying the nanohybrid interfaces. , D.Phil. (Chemistry
- Full Text:
- Authors: Kumari, Renu
- Date: 2018
- Subjects: Biosensors , Nanostructured materials , Bioelectrochemistry
- Language: English
- Type: Doctoral (Thesis)
- Identifier: http://hdl.handle.net/10210/401096 , uj:33504
- Description: Abstract : Two dimensional (2D) materials have provided a new era to biosensors research. Biosensors are functional biodevices which include the integration of biology with electronics. The integration of 2D materials with other nanomaterials has transformed the understanding of the biological and electronics world and has paved a way for the design and fabrication of novel 2D nanointerfaces. The use of 2D nanointerfaces has given great success to biosensors and bioelectronics field which ultimately impacts on biomedical diagnosis and sensing applications. The superior properties of 2D materials such as large surface area, ease of hybridization, good biocompatibility, and high electron transfer properties make them ideal interface materials for the design and fabrication of bioelectronic devices including biosensors. The thesis focused on the fabrication of 2D nanointerfaces by combining two 2D hybrid materials and then nanostructuring with metal nanoparticles for better electron transfer within the interface which is followed by immobilization of enzyme as a bio-recognition element for biosensing purposes. The conjugation of the 2D hybrid nanointerface materials was achieved through the self-assembly technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used in the study for characterization of the 2D hybrid nanointerface structures and chronoamperometry studies were employed to investigate the electrobiocatalytic properties of the 2D hybrid nanointerfaces structures. Structural characterization was done by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques for morphological details of 2D hybrid nanointerfaces structures. The fabrication of bioelectrodes was achieved by using the conjugated 2D hybrid nanointerface materials. ix There are three different segments in this research study. All of these different segments involved the use of 2D materials for bioelectronics purposes. The first phase involved the fabrication of smart hierarchically self-assembled 2D electrobiocatalytic interface system based on the combination of gold nanoparticles (AuNPs) doped graphene oxide (GO)-molybdenum disulfide (MoS2) layered nanohybrid, conjugated with poly (N-isopropylacrylamide, PNIPAAm) resulting in GO/AuNPs/MoS2/PNIPAAm interface. The introduction of PNIPAAm improved the stability of the self-assembled GO/AuNPs/MoS2 interface structure. Horseradish peroxidase (HRP) was subsequently immobilized on the GO/AuNPs/MoS2/PNIPAAm interface through electrostatic interactions giving GO/AuNPs/MoS2/PNIPAAm/Peroxidase electrobiocatalytic interface system as a platform for electrobiocatalysis reactions for biosensing applications. Morphological characterization of GO/AuNPs/MoS2/PNIPAAm indicates that this 2D nanointerface structure has a wide surface area for enzyme immobilization due to their flake-like structure. CV showed diffusion-controlled electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using hydrogen peroxide (H2O2) as a model analyte. The fabricated bioelectrode exhibits a wide linear response to the detection of H2O2 from 1.57 to 11.33 mM, with a detection limit of 3.34 mM (S/N=3) and a capacitance of 8.6 F/cm2. The second phase of the study involved the fabrication of hybrid dual 2D-nanohybrid structure through self-assembly combination AuNPs with hybrid 2D materials consisting of boron nitride (BN) and tungsten disulphide (WS2) as a nanointerface system for electrochemical biosensing. HRP was immobilized on the hybrid dual 2Dnanoparticle systems to form a biointerface. Structural characterization showed high crystallinity in the fabricated structure, while morphological characterization confirmed x the high surface to volume area of the hybrid material and the presence of welldispersed AuNPs. Electrochemical characterization also confirmed that the fabricated HRP/BN/WS2/AuNPs/GC bioelectrode exhibited excellent electron transfer properties at the interface. The electrobiocatalytic activity of the nanohybrid interface structure was studied using H2O2 as a model analyte. The fabricated bioelectrode exhibited a wide linear range from 0.15 mM to 15.01 mM towards detection of H2O2 with a limit of detection of 3.0 mM (S/N = 3) and a sensitivity of 19.16 μA/mM/cm2. Theoretical studies of the BN/Au/WS2(001) nanohybrid structure was carried out using density functional theory (DFT) calculation for confirming the charge transport mobility and conductivity of the fabricated material. DFT calculations combined with the experimental studies showed that the self-assembled combination of the BN/Au/WS2(001) nanocomposite enhances the performance of the fabricated biosensor due to an introduced new electronic state emanating from the N 2p orbital. The third phase of the study involved the synthesis of acetylene sourced graphene (Gr) by chemical vapour deposition (CVD) method. Self-assembly method was used to prepare the 2D nanohybrid interfaces, which consist of Gr, WS2, AuNPs and HRP for fabricating electrochemical biosensor for detection of H2O2. The XRD results revealed that Gr/WS2/AuNPs nanohybrid structure has good crystalline nature. CV and electrochemical impedance spectroscopy results showed that due to the incorporation of AuNPs, the redox properties of Gr/WS2/AuNPs/HRP conjugate 2D hybrid structure improved in comparison to Gr/WS2/HRP. The same trend was observed in the chronoamperometric results. The Gr/WS2/AuNPs/HRP/GCE modified bioelectrode exhibited a good electrobiocatalytic performance towards the detection of H2O2 over a relatively wider linear range (0.40 mM to 23 mM), with a higher xi sensitivity (11.07 μA/mM/cm2) than that of Gr/WS2/HRP/GCE modified bioelectrode (9.23 μA/mM/cm2). The results have shown that electrobiocatalytic reactions can be controlled by modifying the nanohybrid interfaces. , D.Phil. (Chemistry
- Full Text:
Fluorescent molecular sensors based on photoresponsive modified β-cyclodextrin and crown ethers for detecting organic molecules and metal ions in water
- Authors: Ncube, Phendukani
- Date: 2013-12-09
- Subjects: Fluorescence spectroscopy , Cyclodextrins - Synthesis , Crown ethers - Synthesis , Polymerization , Biosensors
- Type: Thesis
- Identifier: uj:7865 , http://hdl.handle.net/10210/8758
- Description: D.Phil. (Chemistry) , The problem of maintaining good quality of water for domestic use and for aquatic life remains a challenge. Water sources are often contaminated with pollutants from natural sources such as volcanic eruptions and by human activities such as manufacturing industries, mining, water-purification processes, agricultural activities and a vast number of other activities. Water-purification processes used by municipal authorities are designed to remove most of the pollutants but some trace amounts will always remain and have been detected in drinking water and treated waste water reservoirs. These trace amounts pose a threat to human health and the well-being of aquatic life. The detection of these trace amounts of pollutants is often carried out by laboratory-based techniques that require sophisticated, expensive instruments and often require extensive sample preparation and pre-concentration. Simple, quick and in-field detection methods are necessary especially for remote small communities with limited or no access to laboratories. Optical detection systems offer hope as a solution to this problem. In this work newly developed fluorescence-based molecular sensors for the detection of pollutants in water were developed, characterised and tested for their sensing abilities towards organic and inorganic pollutants. The fluorescent probes for organic pollutants were designed based on the host-guest chemistry of the cyclodextrin molecule. Azo dye-modified β-cyclodextrins were synthesised and linked via ethylene glycol and epichlorohydrin to produce the sensors that were then tested for their sensing response towards chlorophenols and small aliphatic chlorinated alkanes which are often formed during the disinfection of water in the purification process. The sensor molecules were characterised by UV-Vis, FT-IR and 1D and 2D NMR spectroscopy. The amount of cyclodextrin in each sensor molecule was quantified using the anthrone method (67%) as well as by 1H-NMR spectroscopy (72%). To demonstrate the host-guest interaction of the sensor molecules, isothermal titration calorimetry (ITC) was used. ITC measurements showed that modifying β-cyclodextrin and using linkers did not alter its host-guest interaction with guest molecules as demonstrated by the stoichiometry, n, stability (or binding or association) constant (K) and thermodynamic parameters of the interaction. The sensor molecule linked via ethylene glycol showed selectivity towards 4- chlorophenol among the chlorophenols investigated and has the potential to be used in a sensor for the detection of 4-chlorophenol. The sensor molecule linked via epichlorohydrin showed sensitivity towards chloroform, a typical disinfection by-product. These experimental results showed that the sensor molecules could be used for quick on-field detection of chlorinated organic compounds in water. Sensor molecules for inorganic pollutants were based on the complex formation of crown ethers with metal ions. The sensor was formed by modifying a dibenzo-18- crown-6 ether molecule with an azo dye. The sensor was then characterised using UV-Vis spectrophotmetry, FT-IR and NMR spectroscopies as well as mass spectrometry and CHNS elemental analysis. The sensor molecule was then subjected to different metal ions and the fluorescence change of the probe observed. Interestingly, the sensor was highly sensitive and selective to mercury (II) and Cu (II) ions in water. Mercury (II) is one of the most hazardous heavy metals among the heavy-metal ions found in environmental waters and its early detection in water sources is important. The synthesised molecular sensor can therefore be incorporated into a simple hand-held gadget with a light source and be used for on-field detection of mercury (II) ions in remote areas.
- Full Text:
- Authors: Ncube, Phendukani
- Date: 2013-12-09
- Subjects: Fluorescence spectroscopy , Cyclodextrins - Synthesis , Crown ethers - Synthesis , Polymerization , Biosensors
- Type: Thesis
- Identifier: uj:7865 , http://hdl.handle.net/10210/8758
- Description: D.Phil. (Chemistry) , The problem of maintaining good quality of water for domestic use and for aquatic life remains a challenge. Water sources are often contaminated with pollutants from natural sources such as volcanic eruptions and by human activities such as manufacturing industries, mining, water-purification processes, agricultural activities and a vast number of other activities. Water-purification processes used by municipal authorities are designed to remove most of the pollutants but some trace amounts will always remain and have been detected in drinking water and treated waste water reservoirs. These trace amounts pose a threat to human health and the well-being of aquatic life. The detection of these trace amounts of pollutants is often carried out by laboratory-based techniques that require sophisticated, expensive instruments and often require extensive sample preparation and pre-concentration. Simple, quick and in-field detection methods are necessary especially for remote small communities with limited or no access to laboratories. Optical detection systems offer hope as a solution to this problem. In this work newly developed fluorescence-based molecular sensors for the detection of pollutants in water were developed, characterised and tested for their sensing abilities towards organic and inorganic pollutants. The fluorescent probes for organic pollutants were designed based on the host-guest chemistry of the cyclodextrin molecule. Azo dye-modified β-cyclodextrins were synthesised and linked via ethylene glycol and epichlorohydrin to produce the sensors that were then tested for their sensing response towards chlorophenols and small aliphatic chlorinated alkanes which are often formed during the disinfection of water in the purification process. The sensor molecules were characterised by UV-Vis, FT-IR and 1D and 2D NMR spectroscopy. The amount of cyclodextrin in each sensor molecule was quantified using the anthrone method (67%) as well as by 1H-NMR spectroscopy (72%). To demonstrate the host-guest interaction of the sensor molecules, isothermal titration calorimetry (ITC) was used. ITC measurements showed that modifying β-cyclodextrin and using linkers did not alter its host-guest interaction with guest molecules as demonstrated by the stoichiometry, n, stability (or binding or association) constant (K) and thermodynamic parameters of the interaction. The sensor molecule linked via ethylene glycol showed selectivity towards 4- chlorophenol among the chlorophenols investigated and has the potential to be used in a sensor for the detection of 4-chlorophenol. The sensor molecule linked via epichlorohydrin showed sensitivity towards chloroform, a typical disinfection by-product. These experimental results showed that the sensor molecules could be used for quick on-field detection of chlorinated organic compounds in water. Sensor molecules for inorganic pollutants were based on the complex formation of crown ethers with metal ions. The sensor was formed by modifying a dibenzo-18- crown-6 ether molecule with an azo dye. The sensor was then characterised using UV-Vis spectrophotmetry, FT-IR and NMR spectroscopies as well as mass spectrometry and CHNS elemental analysis. The sensor molecule was then subjected to different metal ions and the fluorescence change of the probe observed. Interestingly, the sensor was highly sensitive and selective to mercury (II) and Cu (II) ions in water. Mercury (II) is one of the most hazardous heavy metals among the heavy-metal ions found in environmental waters and its early detection in water sources is important. The synthesised molecular sensor can therefore be incorporated into a simple hand-held gadget with a light source and be used for on-field detection of mercury (II) ions in remote areas.
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The development of dendrimer-gold composite based electrochemical immunosensor for the detection of cholera toxin in water
- Authors: Tshikalaha, Portia
- Date: 2014-01-14
- Subjects: Water - Toxicology , Cholera toxins , Biosensors , Dendrimers , Gold , Electrochemical sensors
- Type: Thesis
- Identifier: uj:7895 , http://hdl.handle.net/10210/8787
- Description: M.Tech. (Chemistry) , Please read abstract in the full-text document
- Full Text:
- Authors: Tshikalaha, Portia
- Date: 2014-01-14
- Subjects: Water - Toxicology , Cholera toxins , Biosensors , Dendrimers , Gold , Electrochemical sensors
- Type: Thesis
- Identifier: uj:7895 , http://hdl.handle.net/10210/8787
- Description: M.Tech. (Chemistry) , Please read abstract in the full-text document
- Full Text:
Towards HIV sensing : the development of electrochemical DNA/RNA aptamer biosensors on dendrimer-gold platforms
- Authors: Vivian, John Suru
- Date: 2013-07-30
- Subjects: HIV infections - Diagnosis , Biosensors , Electrochemical sensors , Nanomedicine , Nanostructured materials , Dendrimers , Gold
- Type: Thesis
- Identifier: uj:7716 , http://hdl.handle.net/10210/8580
- Description: M.Sc. (Chemistry) , With the increase in the number of new Human Immunodeficiency Virus (HIV) infection and mortality rate worldwide partly due to diagnostic drawbacks which gives false negatives during the window period, it is imperative to find an alternative method of detection. The need for prompt, bed-side and field applicable analytical devices for biomedical purposes cannot be over emphasized in our fast paced world today. As a contribution to meeting these challenges, this dissertation reports (i) the development of novel electrochemical DNA/RNA aptamer biosensor for HIV sensing and (ii) the development of other DNA sequence specific electrochemical biosensors. These biosensors were based on composite platforms of dendrimer and gold nanoparticles...
- Full Text:
- Authors: Vivian, John Suru
- Date: 2013-07-30
- Subjects: HIV infections - Diagnosis , Biosensors , Electrochemical sensors , Nanomedicine , Nanostructured materials , Dendrimers , Gold
- Type: Thesis
- Identifier: uj:7716 , http://hdl.handle.net/10210/8580
- Description: M.Sc. (Chemistry) , With the increase in the number of new Human Immunodeficiency Virus (HIV) infection and mortality rate worldwide partly due to diagnostic drawbacks which gives false negatives during the window period, it is imperative to find an alternative method of detection. The need for prompt, bed-side and field applicable analytical devices for biomedical purposes cannot be over emphasized in our fast paced world today. As a contribution to meeting these challenges, this dissertation reports (i) the development of novel electrochemical DNA/RNA aptamer biosensor for HIV sensing and (ii) the development of other DNA sequence specific electrochemical biosensors. These biosensors were based on composite platforms of dendrimer and gold nanoparticles...
- Full Text:
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