Fast and Sensitive Ionogel Capacitive Sensing of Acetic Acid at Room Temperature for Early Plant Salt Stress Detection

Acetic acid has been identified as an early biomarker of salt stress in plants, enabling precise monitoring of plant health and timely detection of stress. However, its rapid and selective detection at room temperature remains challenging. Herein, we report an ionogel capacitive chemical sensor based on a polydimethylsiloxane (PDMS) matrix incorporating the ionic liquid 1-butyl-3-vinylimidazolium tetrafluoroborate ([VBIM][BF4]). The resulting ionogel sensor exhibits high selectivity toward acetic acid over common volatile organic compounds, originating from solvent effects and electrostatic interactions between acetic acid molecules and the ionic liquid, as revealed by density functional theory (DFT) calculations. Owing to these interactions, the sensor achieves a rapid response time of approximately 6 s at room temperature, and the practical limit of detection is as low as 500 ppb. In addition, the sensor shows excellent long-term stability and mechanical flexibility. The sensor maintains stable sensing performance after 180 days of storage at room temperature and can be integrated with a wireless monitoring system. Furthermore, the sensor detects the acetic acid released by salt-stressed plants, highlighting its potential as an early-warning platform for agricultural stress monitoring.