Metal Oxide Semiconductor Gas Sensors for Breath Analysis: Principles, Selectivity Strategies, and Clinical Perspectives

Noninvasive breath analysis has emerged as a powerful diagnostic approach for early disease detection and personalized health management, as exhaled breath contains a wide range of disease‐specific volatile biomarkers. Among various sensing platforms, metal oxide semiconductor gas sensors have attracted considerable attention owing to their high response, simple device architectures, and excellent compatibility with miniaturized and portable systems. In this review, we focus on the selective detection of clinically relevant breath biomarkers using metal oxide‐based gas sensors and organize recent advances according to key disease‐related gases, including acetone, isoprene, ammonia, hydrogen sulfide, nitric oxide, and hydrogen. For each biomarker, representative material designs and sensor architectures, including catalytic functionalization, compositional control, nanostructure engineering, and filter‐assisted sensing, are discussed in the context of selective and sensitive detection under complex and humid breath environments. We further discuss key challenges for practical breath sensing, including humidity interference, power consumption, and the limitations of single‐biomarker diagnosis. Humidity‐tolerant materials, low‐power miniaturized microelectromechanical systems (MEMS) platforms, machine learning‐assisted analysis, and analytical validation are highlighted as key directions for next‐generation clinically relevant breath sensors.