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

Detecting ammonia (NH 3 ) is crucial for both the atmospheric environment and human health. However, developing low-cost, high-sensitivity, and flexible sensors for NH 3 is a significant challenge. Herein, we report a flexible, electrode-free NH 3 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 NH 3 at 40% relative humidity (RH), room temperature (25°C). The response values were significantly higher than those for other interfering gases including H 2 , CO, H 2 S, and NO 2 . 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 NH 3 levels in breath, offering potential for medical diagnostics and personal health monitoring.