Respiratory illness demands pragmatic clinical monitoring and diagnosis to curb numerous fatal diseases in all aged groups. Due to the complicated instrumentation, long amplification periods, and restricted number of simultaneous detections, present clinically available multiplex diagnostic technologies are difficult to deploy the onsite diagnostic platforms. The futuristic assessment of medical diagnosis eases the respiratory monitoring using exhaled breath, due to the simple and comfort non-invasive detecting techniques. Carbon dioxide (CO₂) stands as a promising biomarker and has been identified in exhaled breath samples that distinguish different respiratory issues. State-of-the-art CO₂ gas sensing strategies are recognized with the growth of modern telecommunication technologies for real-time respiratory illness monitoring and diagnosis using exhaled breath. The presented article reviews the existing CO₂ gas sensors and their developments towards medical applications. With that, the advancement of infrared (IR) CO₂ gas sensors with distinguished light and sensing properties in detecting respiratory disorders are overviewed. The development of optimal CO₂ gas sensing strategy incorporated with Internet of Things (IoT) technology is over-reviewed. The hurdles encountered in the existing research and future preference with real-time CO₂ monitoring and diagnosing respiratory disorders with the advancement attained in IR sensing technology and IoT networking are highlighted.
