Evolution of breath analysis based on humidity and gas sensors: Potential and challenges

Breath analysis is an attractive strategy that holds tremendous potential to achieve non-implantable physical health management enabled by flexible humidity sensors for breathing behaviors (e.g., continuity, frequency) related to disease monitoring and chemiresistive gas sensors related early disease diagnosis. Compared to other techniques for breath component detection, non-invasive breathing diagnostics based on chemical sensors can offer several advantages like miniaturization, low power consumption, simple structure and cost-saving, which is helpful to enhance the portability of practical tests. Although extensive research has been carried out over the past two decades to improve sensing performances of breath gas sensors, many problems need to be further addressed when it comes to clinical disease diagnosis. Developing integrated gas sensor arrays have become one of the efficient solutions to improve detection accuracy. To get rid of external power supply, various novel sensors combining with self-powered technology are designed to exhibit a desirable development prospect in breath analysis. Thus, this review aims to summarize the latest research advances on wearable humidity-enabled breathing behaviors monitoring and typical biomarker gases-based disease screening, and also provides the prospects of future development from individual sensors to integrated devices and self-powered health monitoring systems.