Wearable and Breathable MXene–Textile Sensor for Breath Ammonia Quantification and Joint Motion Tracking

Flexible sensors are often constructed on polymeric or cellulosic substrates, which tend to compromise breathability for mechanical durability, leading to skin irritation and the limitation of long-term use. Here, we develop a monolithic breathable Ti₃C₂T_<i>x</i>@Spandex textile sensor that creates a continuous, gas-permeable conductive network for sensitive response transduction. Impregnated MXene nanosheets give 5.1% response to 300 ppm of NH₃ with a response time of 14 s under folding deformations, full selectivity against 14 interfering gases, and 4 order of magnitude lower resistance (∼5.7 × 10⁸ Ω) than that of bare Spandex (∼1.5 × 10¹² Ω), yielding a signal-to-noise ratio of 20.5 at room temperature. The continuous conductive pathways survive 100% strain, maintain a water-vapor transmission rate of 1149-1268 g m^-2 day^-1, and resolve joint bending angles via reversible Ti₃C₂T_<i>x</i> nanosheet slippage. This breathable, skin-conformable patch enables point-of-care screening of both renal-exhaled NH₃ and real-time joint kinematics.