Metal oxide semiconductor gas sensors in clinical diagnosis and environmental monitoring

Environmental pollution is the main issue in most countries due to industrialization and fossil fuel burning. Pollution affects the quality of air and the fertility of the soil, which causes infections in the respiratory system and affects our immune system through food. Wherefore the environment has to be monitored to regulate its quality as these hazardous gases affect human health and marine life. Another vital requirement in today's medical science is the diagnosis of disease at the earliest through a noninvasive process. These tasks are accomplished by gas sensors that detect noxious gases in the surroundings and are also used in the medical field to diagnose diseases by breathing analysis. Metal oxide semiconductors are extensively used in gas sensors due to their high sensitivity and compatibility but selectivity and high operating temperature are their main drawbacks. This review overviews the major metal oxide semiconductors, the sensing mechanism of chemiresistive metal oxide semiconductor-based gas sensors, and various approaches that have been carried out to overcome their limitations. In this paper, we have reviewed the detection of acetone and ammonia which act as a biomarker for some diseases, and the detection of harmful gases such as alcohol and carbon monoxide using gas sensors developed on metal oxide semiconducting materials for a safe living environment.