Development of an Experimental System for Studying Molybdenum-Indium Oxide Based Chemoresistive Sensors in High Humidity Environments

The issue of gas detection represents one of the primary interests within the entire sensor industry. The analysis of gases has a wide range of potential applications, from monitoring atmospheric quality to analysing the exhalations of living beings. Potentially, the composition of breath can provide a general indication of a person's health status. For instance, elevated levels of hydrogen may signal digestive issues, acetone could be an indicator of decompensated diabetes or fasting, and ammonia is one of the markers for problems with the kidneys, liver, lungs, or teeth. The availability of a non-invasive and non-traumatic method for monitoring various components in breath would facilitate patient care, making the procedure much less traumatic. By contrast, current methods for ammonia level monitoring in hospitals involve blood analysis, which is more time-consuming, requires more resources, and consequently increases the cost of the procedure. Easy-to-use, miniature, sensitive, and selective sensors could significantly improve the quality of life for those in need of medical assistance. This dissertation explores the development and optimization of chemoresistive gas sensors based on molybdenum oxide (MoO₃) doped with indium (In) for the possible application for non-invasive analysis of human breath. The research focuses on enhancing sensor sensitivity, selectivity, and stability under varying environmental conditions, including high humidity and elevated temperatures, which are typical challenges in gas sensing. Comprehensive simulations using COMSOL Multiphysics were conducted to design and optimize the gas sensing chamber, ensuring uniform gas distribution and minimizing stagnant zones, thus improving sensor accuracy and response time. The synthesis of MoO₃-based sensors involved various doping concentrations and morphologies to investigate their impact on gas sensing performance. The fabricated with two methods sensors were rigorously tested for their response to ammonia, acetone, and ethanol under controlled conditions. The results demonstrated that In-doped MoO₃ sensors exhibit high sensitivity and selectivity for ammonia, making them promising candidates for medical diagnostics. Overall, this research contributes to the development of advanced gas sensing technologies that could revolutionize non-invasive medical diagnostics, offering a practical and cost-effective alternative to traditional methods. The findings have significant implications for improving patient care, particularly in monitoring and managing chronic conditions through breath analysis.