Ternary Heterojunction-Reinforced Room-Temperature Flexible NH3 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.