Intermolecular Interaction-Assisted Selective Sensing Using an MXene-Based Chemoresistive Sensor

MXene, a family of two-dimensional (2D) layered materials, finds potential applications in gas sensors; however, sensors fabricated with pristine MXene generally suffer from poor selectivity. Herein, we demonstrate tunable selectivity in MXene-based sensors by modifying the surface functionality of MXene layers with 4-bromotriphenylamine (TPA) and 11-mercaptoundecanoic acid (MUA). The intermolecular interactions between analyte molecules and the functionalized MXene surface enable a tunable and selective response to hydrogen bond-rich molecules: MUA-MXene shows preferential sensitivity to methanol, whereas TPA-MXene exhibits an enhanced response to ammonia. Surface functionalization simultaneously improves both the response sensitivity and response time. Furthermore, our results reveal that surface-absorbed water plays a critical role in maintaining a stable gas response, particularly interflake water molecules that facilitate hydrogen bonding between MXene channels and gas molecules. We also developed a stretchable MXene-based ammonia sensor by integrating elastic substrates, stretchable electrodes, and TPA-MXene film. This sensor demonstrates remarkable and stable performance in detecting ammonia (100 to 1000 ppm of NH₃ at 80% relative humidity) under mechanical strain, maintaining functionality under 40% parallel strain and 20% perpendicular strain over a two-month period. The robustness suggests potential applications in breath analysis.