Multiscale Structural Engineering of a Wearable Gas Sensor for Simulated Breath Ammonia Monitoring Under High‐Humidity Conditions

ABSTRACT Wearable gas sensors capable of monitoring volatile biomarkers in exhaled breath offer a promising approach for non‐invasive health monitoring. However, existing wearable sensors are hindered by insufficient sensitivity, limited selectivity, and pronounced humidity interference under breath‐relevant conditions. Herein, we developed a multiscale‐engineered wearable NH 3 sensor based on a flexible polyvinylidene fluoride (PVDF)/PANI‐PSS/SnO 2 /YSZ (yttria‐stabilized zirconia) nanofiber network. At the nanoscale, a crystalline‐amorphous PANI/SnO 2 heterointerface enhances signal transduction efficiency, thereby improving sensing sensitivity. At the molecular level, PSS functionalization introduces abundant acidic sites that promote NH 3 chemisorption, thus enhancing selectivity and sensitivity. At the macroscale, the YSZ nanofiber network functions as a strain‐tolerant substrate, while the hydrophobic PVDF encapsulation suppresses humidity interference, together ensuring mechanically flexible and stable sensing performance. Notably, the gas sensor exhibits a theoretical detection limit of 18.5 ppb and maintains stable NH 3 sensing performance under high‐humidity conditions (≥85% RH) and in the presence of interfering gases. Furthermore, the wearable sensor was integrated into a portable wireless sensing platform, enabling simulated breath NH 3 measurements to be transmitted to a mobile terminal for real‐time visualization. This work establishes a generalizable multiscale design strategy for exhaled breath gas sensing, advancing wearable platforms for continuous non‐invasive health monitoring.