Atomic sulfur-bonded titanium carbide nanosheets for flexible piezoresistive sensor in monitoring sleep apnea syndrome

Flexible piezoresistive sensors have attracted great attention for the real-time monitoring of sleep apnea syndrome (SAS) through respiratory airflow. Although two-dimensional ultrathin Ti₃C₂ is regarded as a promising piezoresistive material, its poor structural compressibility and antioxidation limit its practical applications. Here, an innovative atomic sulfur-bonded strategy is proposed to fabricate large-sized, crumpled, and antioxidative Ti₃C₂/Na₂S (TS) flakes for preparing flexible piezoresistive sensors. The fundamental mechanism is rooted in the synergistic effect of lateral boundary assembly of Ti₃C₂ nanosheets into large flakes (∼7 μm), lattice distortion to induce crumpled structures, and edge passivation by S²⁻ ions to mitigate oxidation (105 days). The crumpled microstructure provides abundant voids for enhanced compressibility and contact site variability, resulting in a 5-fold sensitivity improvement over the Ti₃C₂ sensor and an ultralow detection limit of 0.2 Pa. We demonstrate the practical application of highly sensitive and stable piezoresistive sensors integrated into a respiratory monitoring system for SAS detection.