Chemiresistive Gas Sensors: Materials, Mechanisms, and Applications on the Road to Intelligence and Multifunctionality

Advances in chemiresistive gas sensors (CGSs) are driving their evolution toward multifunctionality and intelligence. Nevertheless, it remains crucial to track the latest developments and clarify the key contributions of materials and structural engineering in enabling these capabilities. First, this review describes the key performance metrics of CGSs and summarizes the characteristics and transduction mechanisms of representative sensing materials, including metal-oxide semiconductors (MOSs), carbon nanomaterials (CNs), conducting polymers (CPs), MXenes, two-dimensional transition-metal dichalcogenides (2D TMDs), and other emerging materials. Next, major performance-enhancement strategies are discussed in response to the intrinsic limitations of CGSs, covering nanostructure and morphology engineering, heterostructure construction, chemical doping and surface functionalization, and composite/hybrid engineering, as well as humidity interference and corresponding mitigation approaches. Further, advances in applications spanning environmental, medical, industrial, and food-related scenarios are surveyed, with a focus on material selection and performance evaluation. Building on these developments, the latest progress in advanced CGSs is highlighted, particularly wearable sensing, self-powered operation, machine-learning (ML)-assisted pattern recognition, and integration with wireless communication systems. Finally, the major challenges currently facing the field are identified, and perspectives on future research trends are provided.