Repository logo
 

Theses and dissertations (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/6

Browse

Has files: YesSubject: search.filters.subject.Chemical detectors

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Development of an electrochemical immunosensor for the detection of steviol glycosides by experimental and computational methods
    (2020-04) Hloma, Phathisanani; Bisetty, Krishna; Sabela, M. I.; Kanchi, S.
    An electrochemical immunosensor employs antibodies as a capture and detection mechanism to produce an electrical charge for the quantitative analysis of target molecules. The current analytical methods for the separation and detection of stevia glycosides can be tedious in terms of sample preparation and the lack of selectivity. However, electrochemical immunosensors provide selective, sensitive and costeffective detection routes for these widely consumed sweeteners. In this study, the author developed an electrochemical immunosensor for the detection and quantification of steviol glycosides, a non-nutritive sweetener widely employed in the food and beverage industries. Most of the artificial sweeteners are low-calorie sweeteners recommended for health-related illnesses. The stability of these sweeteners at even high temperatures has increased their applications in foodstuffs widely. Constant exposure to these sweeteners is somehow associated with health complications, as some are cancer-causing agents. Although there are no reports on stevia glycosides as a health risk sweetener, its widespread use in the food industry needs to be regulated. Herein, the developed immunosensor was achieved by fabricating the platinum electrodes with graphene oxide (GO) assimilated in Zinc Oxide nanoparticles (ZnONPs) with multiwalled carbon nanotubes (MWCNTs) and immobilized with the human sweet receptor subunit T1R2. The electrochemical detection of the natural sweetening compound, Rebaudioside A (Reb A) was evaluated qualitatively and quantitatively using cyclic and differential pulse voltammetry, respectively under optimised conditions in pH 11 borate buffer from -0.4 V to 0.8 V vs Ag/AgCl. The GO/MWCNT/ZnONPs nanocomposite was characterized using High-resolution Transmission Electron microscope (HR-TEM), Thermogravimetric Analysis (TGA), Attenuated Total Reflection Mode Fourier transform infrared (ATR-FTIR) and UV-VIS spectroscopy characterization techniques. Also, asymmetric flow-field-flow fractionation and centrifugal flow-field-flow fractionation equipped with a UV-vis and multi-angle angle light scattering detectors were used to separate and characterize the size distribution of the synthesised ZnO nanostructures. The field flow fractionation (FFF) is one of the efficient separation techniques known, and centrifugal flow fieldflow fractionation separates different particle sized nanoparticles by density, thus determining size variation within the synthesised batch. The results obtained using FFF were compared and validated with the conventional characterisation techniques described above. Computational studies were used to supplement experimental results using docking and adsorption methods. Adsorption studies were carried out to better understand the mechanistic aspects between T1R2, the nanocomposite used to modify the platinum working electrode, and the analyte Reb A. Docking studies between the T1R2 receptor and the steviol glycosides were used to explore the interaction and mechanism of the immunosensor detection. The results of this study may contribute to the development of an immunosensor that can potentially be used to quantify steviol glycosides in the food and beverage industry
  • Thumbnail Image
    Item
    Fabrication of sensors for the sensitive electrochemical detection of anti-tuberculosis drugs
    (2018) Chokkareddy, Rajasekhar; Redhi, Gan G.; Kumar, Bhajanthri Natesh
    In this work, electrochemical biosensors have been developed and quantified the pyrazinamide, isoniazid, rifampicin, ethambutol and streptomycin drugs in various pharmaceutical samples. Electrochemical methods are versatile and powerfull analytical technique of immense value in the area of pharmaceutical analyses. In addition, due to the similarity in the biological and electrochemical reactions, it can be expected that the reduction-oxidation mechanisms occur at the electrode surface. The biologically stimulated molecules can be examined by electroanalysis and they are also outstanding tools for the detection of pharmaceutical complexes in various matrices. Although in the case of a biosensors, the analyte interacts with bioreceptor and the resultant output is measured by a specifically designed transducer. Additionally, a reliable highly sensitive and novel biosensor was developed by using a glassy carbon electrode modified with various nanomaterials. Hence horseradish peroxidase (HRP) - Multiwalled carbon nanotubes (MWCNTs)-Titanium oxide nanoparticles (TiO2NPs) fabricated glassy carbon electrode (GCE) were used for the determination of isoniazid. Similarly, copper oxide nanoparticles (CuONPs)-MWCNTs immobilized with Cytochrome c (Cyt c) on glassy carbon electrode were established for the detection of pyrazinamide. Furthermore, iron oxide nanoparticles (Fe3O4NPs) and MWCNTs composite were immobilized with Coenzyme q (Coen- q) on glassy carbon electrode for the detection of rifampicin. In addition, Cyt c immobilized with ZnONPs and MWCNTs on glassy carbon electrode for the determination of streptomycin. Finally, the glassy carbon electrode fabricated with zinc oxide nanoparticles (ZnONPs) and reduced graphene oxide (RGO) nano composite, was further immobilized with HRP to enhance the electrochemical performance of the modified electrode for the determination of ethambutol. Electrochemical behaviour of these first line anti TB drugs to the developed biosensors were examined by using cyclic voltammetry and differential pulse voltammetry under the optimum experimental conditions such as scan rates, pH, accumulation potential, pulse amplitude, accumulation time, voltage step time, voltage step and deposition time respectively. The prepared biosensors and nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermo gravimetry (TGA) and x-ray diffraction (XRD). It was observed that electrochemical methods provided good and effective techniques for the determination of isoniazid, pyrazinamide, rifampicin, ethambutol and streptomycin. Compared to the other analytical methods, the limit of detection and limit of quantifications were found to be 0.0335 μM and 0.1118 μM for isoniazid, 0.0038 μM and 0.0129 μM for pyrazinamide, 0.032 µM, and 0.413 µM for rifampicin, 0.0214 μM and 0.6713 μM for ethambutol, and 0.0028 μM and 0.5628 μM for streptomycin respectively.
  • Thumbnail Image
    Item
    Evaluation of bacteriological techniques, sensory evaluation, gas chromatography, and electronic nose technology for the early detection of Alicyclobacillus acidoterrestris in fruit juices
    (2007) Harrichandparsad, Zeenat
    Alicyclobacillus acidoterrestris is a spore-forming spoilage micro-organism found in fruit juices whose spores are not destroyed by typical pasteurisation. Once its spores outgrow and multiply in finished juice products, they produce two volatile taint compounds namely guaiacol and 2,6-dibromophenol. In the food industry margins for errors are small and monitoring of products to avert such errors is crucial. Conventional microbiological monitoring is one such technique for spoilage micro-organisms another being automated systems which can detect taints. Both these categories were evaluated in this study with the electronic nose and gas chromatograph being the specific automated systems being assessed. Sensory evaluation was also assessed as a diagnostic tool in the detection of taints. Isolation and identification of what was thought to be A. acidoterrestris was a laborious and expensive exercise which eventually proved inconclusive. A pure culture was purchased and juices were then inoculated with two levels of A. acidoterrestris spores and incubated. Juices from each level of inoculation were evaluated at different time intervals via the above-mentioned monitoring techniques. Of the three media assessed in the microbiological method, Bacillus acidoterrestris medium (BAM) was found to be the most effective for enumerating A. acidoterrestris followed by K-medium (KM) then Orange Serum Agar (OSA). While BAM was still indicating the presence of A. acidoterrestris KM and OSA were not (counts of <10cfu/g). This illustrated that this micro-organism could be easily overlooked if KM or OSA were being used to enumerate them. Considering that many workers actually do use KM and OSA as their media of choice in enumerating A. acidoterrestris (perhaps because BAM is very tedious to prepare) the cause for concern is a real one. Assessment of the resultant taints via sensory evaluation after inoculation and incubation reveals the inability of many panellists to detect taints at levels (as assessed by GC) far above their documented threshold values. While GC is an extremely useful and powerful tool, the level of expertise and skill required to use such an instrument cannot be overlooked nor can the expense involved. With regard to the electronic nose assessment for the presence of the volatile taint compounds, an important finding was that the electronic nose indicated significant differences between test and control samples when panellists performing sensory evaluation did not. This also correlated to an interval when enumeration on OSA illustrated no A. acidoterrestris after several days of inoculation and incubation and BAM and KM did. Without implying that the electronic nose has no drawbacks, it has proved, in this instance to be a simple and easy piece of equipment to use. It can be used to detect taints produced under simulated spoilage conditions at reduced analysis times, levels of expertise, cost and energy.