Investigation of electrode-free, room temperature, flexible NH3 sensors with high stability and sensitivity using MXene@PANI-MWCNTs ink.

Detecting ammonia (NH3) is crucial for both the atmospheric environment and human health. However, developing low-cost, high-sensitivity, and flexible sensors for NH3 is a significant challenge. Herein, we report a flexible, electrode-free NH3 sensor based on an ink of polyaniline-covered MXene and multi-walled carbon nanotubes (MXene@PANI-MWCNTs), which was developed on cotton fabric using a dispensing print method. After optimizing the MXene@PANI-MWCNTs concentration, the number of sensor arms and the printed layers, the sensor exhibited a high response in the range of 0.5-25 ppm and can detect as low as 0.5 ppm NH3 at 40% relative humidity (RH), room temperature (25°C). The response values were significantly higher than those for other interfering gases including H2, CO, H2S, and NO2. Furthermore, the sensor demonstrated excellent mechanical stability, with its response dropping by only 3.7% after 1000 bending cycles. When covered with expanded polytetrafluoroethylene (e-PTFE) film, the sensor showed stable performance in the ranging of 30%-90% RH at 25°C. Additionally, MXene@PANI-MWCNTs ink was printed on masks to detect NH3 levels in breath, offering potential for medical diagnostics and personal health monitoring.