Saudi Cultural Missions Theses & Dissertations
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Item Restricted Development of An Electrochemical Immunosensor for Environmental Monitoring of Polychlorinated Biphenyls (PCBs) in Soil Environment(Saudi Digital Library, 2023-04-24) Alsefri, Samia; Maguire, AnitaPolychlorinated biphenyls, PCBs are a type of chemical contaminant known as persistent organic pollutants (POPs). They consist of biphenyl molecules covalently bonded with one to ten chlorine atoms. PCBs pose a threat to ecosystems and food safety due to their high toxicity, long-term stability, poor degradation, and bioaccumulation. The current methods, although sensitive, have their limitations, for example, time-consuming, laborious, and costly. Further, the instrumentation cannot be used for on-site analysis. The aim of this research is to develop a novel electrochemical method that will be capable of providing a direct, portable, cost-effective, and easy method for analysing and monitoring PCBs in the environment. For the first time, a self-assembled monolayer was used to modify an electrode as a method for fabricating a transducer for detection of PCBs by using a gold electrode, it was modified with 11- mercaptoundecanoic acid (11-MUA), and the activation of the carboxylic acid terminal was performed by cross-linking 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hyrodsuccinmide (NHS). The electrochemical behaviour of the electrode was investigated by CV (Cyclic Voltammetry), LSV (Linear Sweep Voltammetry) and EIS (Electrochemical Impedance Spectroscopy) using a ferrocyanide/ferricyanide redox pair. It was found that the indirect competitive assay showed the best performance for Aroclor1254 detection, with a commercial Polyclonal chicken antibody (IgY) specific to PCB was used as primary antibody. The limit of detection was found at 0.20 ng/ml using bare gold electrode. However, the sensitivity of the sensor was increased after the electrode surface modification was found at 0.09 ng/ml. A novel electrochemical immunosensor method showed a good performance with a 3-fold decrease in sensitivity achieved after the surface modification. The electrode coated with coating conjugate was found stable for more than 25 days at 4 ˚C. In conclusion, this Ph.D. thesis demonstrates that the integration of electrochemical techniques with immunoassay methods can achieve detection limits as low as required for in-situ and real-time analysis of soil samples. It was found that the electrochemical immunosensor method showed better results compared to ELISA and that was verified with GC-MS. The usage of this a novel electrochemical immunosensor as a complement to the electrochemical studies not only enhanced the quality of the research but also contributed to the construction and improvement of immunosensors. As a result, they represent an accurate and a new robust method that can be applied to microsensors and microfluidic systems for the effective control and prevention of PCBs in the environment.8 0Item Restricted Reusable electrochemical impedance spectroscopy biosensor for the detection of cortisol in sweat: Introducing novel techniques suitable for future affective wearable devices and emotional stress.(2023) Zamkah, Abdulaziz; Sherratt, Simon; Andrews, SimonSkin conductivity is used in emotion and stress-detecting systems based on physiology (sweat). However, these technologies do not detect sweat biomarkers or utilize sweat's biological information. Stress-induced volatile organic compounds (VOCs) cannot be detected using these methods. This study explores biomarkers of human emotional stress and identifies key indicators for wearable sensors in affective systems. Crime, health, the economy, and quality of life are all affected by emotional stress. Blood cortisol testing, electroencephalography, and physiological parameter techniques are the gold standards for stress measurement; nevertheless, they are expensive, inconvenient, and impractical for wearable real-time stress monitoring, such as a smartwatch, due to their single-use design. Instead, sweat cortisol was found as the critical stress biomarker for wearable affective system sensors in this study. Modern sensor research aims to create synthetic receptors with similar selectivity and sensitivity to natural antibody-antigen behaviour. This molecular recognition could lead to selective, sensitive sensors that can identify and monitor targets noninvasively when paired with modern methods for monitoring recognition element modifications. Molecularly imprinted polymers, MIPs, are synthetic antibody-antigen systems. They selectively bind their production molecule using a "lock and key" method. MIPs may offer biological receptor specificity and selectivity with environmental durability and low cost. The current study explores the feasibility of using MIPs technology to detect cortisol in sweat for real-time monitoring of emotional stress episodes. A conceptual approach is given to make MIPs sensors more usable for monitoring cortisol sweat in wearable devices. As seen in the reviewed literature, cortisol and MIPs are under-researched biomarkers and their biosensors from the reviewed literature. Experiments employing electrochemical impedance spectroscopy techniques on a capacitance MIP confirmed this theory. It successfully detects cortisol within the physiological range as the higher response is recorded for a greater concentration. The literature also shows that no MIP biosensor is reusable in portable electronics. This work used a function generator simulation to evaluate the hypothesis that the target extraction technique employed Abstract Abdulaziz Zamkah 2023 Page iii during the MIPS fabrication step is repeatable and suitable for employment in wearables.21 0