Ionic-gel-gated CNT-FETs for VOCs sensing: an anion-dominated solvation orthogonal selectivity

The detection of volatile organic compounds (VOCs) and their mixtures is of increasing importance in environmental monitoring and breath analysis-based disease diagnosis. Field-effect transistors (FETs) show potential for VOCs detection due to their inherent signal amplification and high sensitivity. Ionogel, with its unique electric double-layer capacitance and high polarity, offers excellent molecular enrichment for gas sensing. Accordingly, this work reports an ionogel-gated carbon nanotube-FET (IG-CNTFET) that achieves near-orthogonal selective detection of dimethyl methylphosphonate (DMMP) and triethylamine (TEA) by designing distinct ionogel materials as the gate dielectric. The mechanism originates from an anion-dominated interfacial solvation and polarization process. Different anions regulate the local solvation environment and charge distribution of the ionogel, thereby controlling the selective partitioning and interfacial enrichment of gas molecules. Owing to its charge-delocalized and weakly coordinating nature, TFSI - preferentially accommodates highly polar DMMP molecules and promotes their accumulation near the ionogel/CNT interface. In contrast, PF 6 - provides a distinct ionic environment for TEA enrichment, leading to a pronounced negative threshold-voltage shift. These analyte-specific interfacial responses ultimately enable orthogonal gas-sensing behavior. The device exhibits exceptional tunable sensing performance. Adjusting the gate voltage significantly enhances the response signal and selectivity toward the target gases. Notably, the sensor achieves a detection limit as low as 600 ppb for DMMP, and 100 ppb for TEA. In contrast, the sensor shows negligible responses to other common VOCs, such as ethanol, n-hexane, and acetone. This work provides a crucial material design strategy for developing next-generation ionogel-based gas sensors.