ANALYSIS AND OPTIMIZATION OF COLORIMETRIC NANOSENSORS FOR RAPID DETECTION OF MICROBES IN WATER

Access to safe water is a basic human right recognized by the United Nations General Assembly in 2010 (WHO, 2020). However, a least 2.2 billion people globally still are without safely managed water services meaning they use a drinking water source that can be contaminated with faeces (WHO, 2020). With such a pressing global health issue, it is clear that improvement to water systems is important and required in the Agenda 2030 Sustainable Development Goals (SDGs). However, to improve water systems and prove they are safe water sources, water quality testing must occur. A solution to this issue is the development of rapid detection sensors for pathogens in water. The first chapter of this thesis aims to create an informed list of rapid detection sensors that should be focused on for future development. This is achieved by using multicriteria decision analysis techniques based on using two consecutive processes. The first is the Analytic Hierarchy Process (AHP), which was used to develop weightings for criteria being measured for different sensor alternatives. The second process is the Technique of Order Preference Similarity to the Ideal Solution (TOPSIS), which was used to perform the ranking of the sensors being reviewed based on the weighted criteria. The outcome of the multicriteria decision analysis was identifying the top 5 rapid detection nanosensors for future development. They can be further improved to include field scale applications while also achieving lower detection limits and shorter detection times. The cost for these sensors could possibly be reduced by changing the nanoparticles that the sensor is composed of. Through improved methods, the goal of creating a cost effective, rapid-detection nanosensor for bacteria (e.g., Shiga-toxin producing E. coli) in drinking water can be achieved by prioritization of research on these promising nanosensors. The second chapter of the thesis focuses on optimizing a gold nanosensor developed in 2015 by Raweewab T. and Rawiwan L, hereafter called the “Original Method.” The goal was to reduce the cost and improve the reusability of their indirect colorimetric gold nanosensor without compromising the simplicity of the detection platform. With a reusable and more cost-effective sensor, field applications for water quality testing in water system projects in impoverished areas can be more obtainable. The nanoparticle itself was the target of optimization in this study. The hypothesis was that the polyethylenimine (PEI) coating on the gold nanoparticle surface is the governing factor of how the sensor functions, meaning the core nanomaterial does not affect the function of the sensor. In this study, the results showed that sensor still maintained its function after replacing the PEI coated gold nanoparticle used in the Original Method with PEI coated silver nanoparticles. These findings indicated that with further development and future research, it will be possible to use less expensive nanoparticles for making the nanosensor. It will also be possible to make this sensor reusable through the development of PEI coated magnetite nanoparticles. Their magnetic quality could allow for recovering the nanosensors from the test media, then re-conditioned and used again