Ternary Heterojunction-Reinforced Room-Temperature Flexible NH ₃ Sensor with Enhanced Sensitivity and Ultralow Detection Limit

The development of flexible ammonia (NH₃) sensors with high sensitivity, selectivity, and stability at room temperature is of great importance for continuous and accurate monitoring applications. In this study, we present a high-performance, room-temperature flexible NH₃ sensing chip based on a dual heterojunction enhancement mechanism. The device is fabricated on a flexible polyethylene terephthalate substrate with Au interdigitated electrodes, and utilizes PPy/(001) TiO₂/MXene (PTM) ternary nanocomposites with 3D nanostructures, synthesized via hydrothermal treatment and in situ polymerization, as the active sensing layer. The construction of dual heterointerfaces, including PPy/(001) TiO₂ and PPy/MXene, significantly enhances the sensor's performance. Operating at room temperature, the sensing chip exhibits outstanding characteristics, including a high response of 164.42% to 10 ppm of NH₃, an ultralow detection limit of 5 ppb, and a rapid response time. Moreover, the PTM-based sensor demonstrates excellent selectivity, long-term stability, and mechanical durability, with only a 1.9% decline in response after 500 bending cycles. Notably, it retains high detection sensitivity even under high-humidity conditions. Owing to these superior properties, the PTM-based sensor chip was successfully applied for real-time NH₃ monitoring during food spoilage and for distinguishing NH₃ concentrations in exhaled breath among healthy individuals, gastric ulcer patients, and end-stage renal disease patients. These findings highlight the strong potential of this sensor for applications in food safety monitoring and noninvasive medical diagnostics.