Date of Award

August 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Wayne Seames

Abstract

There is a continuous release of various pollutants such as NOx, CH4, CO, NH3 and various volatile organic compounds (VOCs) from industrial emissions, automobile exhausts, and household waste causing many health and environmental issues such as acid rain, global warming, and ozone layer depletion. To minimize and control these issues there is a huge demand for monitoring/sensing units that can detect low (ppt-ppm level) concentrations of these air pollutants quickly and efficiently. In addition to air pollution monitoring, there is an emerging field of exhaled breath analysis for use as noninvasive, quick and portable health diagnosis methods. Electronic nose (E-Nose) technology is one class of exhaled breath analyzers. The goal is to measure a characteristic profile of exhaled VOCs resulting from cellular metabolism associated with various diseases, such as viral infections and to match the measured profile to baseline profiles in order to predict the presence of a specific disease. Artificial intelligence (AI) technology can be utilized to assist in profile matching. For both ambient monitoring and exhaled breath analysis, gas sensors can sample and detect target molecular information which can be translated into the information needed for AI algorithms to predict, prepare, and respond to unexpected future events related to our health and the environment. The goal of the work documented herein, is to expand and improve the breadth of knowledge associated with exiting sensor technology. The research results summarized in this dissertation are organized into two chapters, chapter II and chapter III, which focus on initial research for developing unique nanomaterial-based chemiresistive sensors. These can be used to detect the concentration of various gases and VOCs in the environment. (chapter II) and for medical diagnosis, e.g. human breath analysis (chapter III) with enhanced sensitivity, selectivity, power consumption and reduced response and recovery time. Chapter II, “Development of a Nitric Oxide Detector” covers research efforts for the development of novel nanomaterials based on gold functionalized carbon nanotubes and their implementation to make a chemiresistive sensing devices. These sensors can detect as low as 10 ppb nitric oxide in both air and nitrogen environments over a wide relative humidity range (0–97%). These novel material-based sensors have exceeded the sensitivity and working humidity range offered by currently available sensors without requiring humidity control, thus making them an ideal choice for applications where high humidity is inevitable such as NO mapping in deep ocean environments and NO measurements in human breath as a biomarker for lung disease. Preliminary results demonstrate that this sensor’s approach is feasible. Given its widespread potential applications ranging from automobile industries to medical diagnosis there is scope for commercialization. Chapter III, “Development of an E-Nose for COVID-19 Detection” details a development of nanosensor-based E-Nose prototypes similar to a human olfactory system, allowing for the conduction of on-site, rapid screening for COVID-19 infection by measuring the pattern of sensor responses to VOCs in exhaled human breath. The E-Nose device consists of 64 unique sensing materials. About 20 of the 64 materials responded significantly to individual COVID-19 biomarkers. By identifying various combinations of VOCs, the E-Nose can determine if the sensor profile corresponds to heathy breath emissions or to typical COVID breath emissions at parts-per-billion (ppb) levels. These sensor elements also showed repeatability of 0.02% and reproducibility of 1.2%. Preliminary clinical testing at Stanford Medicine with 63 participants showed an accuracy of 79% in discriminating COV+ and COV- human breath using a linear support-vector machine (SVM) model. Previous studies for COVID-19 detection using exhaled breath used bulky benchtop spectrometry instruments which required time-consuming breath sample preparation and trained operators making these applications not attractive for use in real-time screening. The E-Nose prototype developed in this research can provide a total screening time of less than 2 minutes which is compatible with the wide-scale screening in busy public places. The current 64 nanosensing materials showed response to a wide range of VOCs belonging to various groups of chemicals such as alcohols, easters, aldehydes, alkanes, aromatics, ketones etc., which makes them capable for the detection of other VOCs biomarkers for other potential applications in industrial, environmental, residential, food, military and medical fields. Sensitive and selective sensing materials, good repeatability and reproducibility, quick response and recovery time, small hand-held size, low power consumption and a swappable sensor head all make this technology attractive for commercialization.

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