Faculty of Applied Sciences
Permanent URI for this communityhttp://ir-dev.dut.ac.za/handle/10321/5
Browse
2 results
Search Results
Item Development of electrochemical biosensors for sweeteners using engineered nanomaterials supported by computational modelling(2024-05) Hloma, Phathisanani; Bisetty, Krishna; Sabela, Myalowenkosi Innocent; Uwaya, Gloria EbubeElectrochemical immunosensors are a powerful tool in analytical applications. The current methods for the isolation and detection of artificial and natural sweeteners suffer from challenges in sample preparation and a lack of specificity. However, electrochemical immunosensors offer a sensitive, economical, and selective analytical solution to analyse these commonly used sweeteners, such as aspartame. The author of this work developed electrochemical immunosensors for the food and beverage industries to use in the detection and measurement of aspartame, a non-nutritive sweetener, and rebaudioside A, a natural sweetener. Most artificial sweeteners are low-calorie options that are suggested for ailments linked to health. These sweeteners' ability to remain stable at even high temperatures has greatly expanded the range of meals that can use them. Aspartame and rebaudioside A have not been linked to any health risks, although regulation is still necessary because of their extensive use in the food industry. The developed immunosensors for the detection of aspartame and rebaudioside A were achieved and presented as three case studies in this study. In the first case study, the immunosensor was achieved by fabricating green synthesized PVP capped silver nanoparticles (PVP-AgNPs) with functionalized multi-walled carbon nanotubes (fMWCNTs) and immobilizing the human sweet tase receptor T1R2 in a glassy carbon electrode (GCE), resulting in GCE/PVP-AgNPs/fMWCNTs/T1R2. The electrochemical assessment of aspartame was achieved using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV), respectively, under optimum pH 8 in a 0.1 M phosphate buffer with reference to the Ag/AgCl reference electrode. The electro-oxidation of ASP was noticed by a well-defined oxidation peak potential at 1.4 V. The immunosensor sensor showed a linear dynamic range of 2.89 to 27.61 μM (R 2 = 0.9170) based on differential pulse voltammetry, with limits of detection (LOD) and quantification (LOQ) (S/N = 3) of 0.40 μM and 1.34 μM, respectively. The second case study focused on the indirect electrochemical detection of rebaudioside A in the presence of ferro/ferricyanide as a redox probe. The immunosensor was developed by fabricating GCE with zeolitic imidazolate framework-67 (ZIF-67) in combination with fMWCNTs and the immobilization of the T1R2 receptor. The qualitative and quantitative analysis of rebaudioside A was done using CV, EIS, and DPV utilizing a 5 mM [Fe (CN)6] 3-/-4 redox probe. The stable electrode had an exponential dynamic range of 0.9901 µM to 8.2569 µM (R2 = 0.9996). The LOD and LOQ were computed to be 1.10 µM and 3.33 µM, respectively. This case study also used Patch Dock and PyRx to better understand the interactions between Reb A and T1R2. The final case study employed a platinum electrode (PtE) as the working electrode (WE) for the electrochemical immunosensing of aspartame. The modification of PtE involved the utilization of a nanocomposite consisting of PVP-AgNPs and reduced graphene oxide (rGO), with T1R2 immobilized. The electrochemical detection of aspartame was achieved under optimized conditions at pH 8 in a 0.1 M phosphate buffer, utilizing CV, EIS, and DPV as electrochemical tools. The PVP-AgNPs/rGO/T1R2 was used to fabricate Pt and the electrode performed well with a linear increase in oxidation peak currents as aspartame concentrations were increased from 2.38 µM to 25.78 µM (0.9529). The LOD and LOQ were calculated to be 5.85 µM and 17.73 µM, respectively. The synthesized nanoparticles and nanocomposites (PVP-AgNPs/fMWCNTs, ZIF 67/fMWCNTs, and PVP-AgNPs/rGO) were characterized using conventional techniques such as UV-Vis spectroscopy, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), field flow fractionation (FFF), single particle inductively coupled plasma mass spectrometry (sp-ICPMS), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). In addition to the experimental results, computational chemistry methods were undertaken. These included adsorption assessments, density functional theory (DFT), and molecular docking techniques. These techniques were all aimed at achieving a deeper molecular-level understanding of the interactions among the analytes (Aspartame and Reb A), T1R2, and the nanocomposites employed in the modification of the working electrodes (GCE and Pt-E)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