Flexible Chemiresistive Cyclohexanone Sensors Based on Single-Walled Carbon Nanotube-Polymer Composites

We report a chemiresistive cyclohexanone sensor on a flexible substrate based on single-walled carbon nanotubes (SWCNTs) functionalized with thiourea (TU) derivatives. A wrapper polymer containing both 4-vinylpyridine (4VP) groups and azide groups (P(4VP-VBAz)) was employed to obtain a homogeneous SWCNT dispersion via noncovalent functionalization of SWCNTs. The P(4VP-VBAz)-SWCNT composite dispersion was then spray-coated onto an organosilanized flexible poly(ethylene terephthalate) (PET) film to achieve immobilizing quaternization between the pyridyl groups from the polymer and the functional PET substrate, thereby surface anchoring SWCNTs. Subsequent surface functionalization was performed to incorporate a TU selector into the composites, resulting in P(Q4VP-VBTU)-SWCNT, for the detection of cyclohexanone via hydrogen bonding interactions. An increase in conductance was observed as a result of the hydrogen-bonded complex with cyclohexanone resulting in a higher hole density and/or mobility in SWCNTs. As a result, a sensor device fabricated with P(Q4VP-VBTU)-SWCNT composites exhibited chemiresistive responses (ΔG/G₀) of 7.9 ± 0.6% in N₂ (RH 0.1%) and 4.7 ± 0.4% in air (RH 5%), respectively, upon exposure to 200 ppm cyclohexanone. Selective cyclohexanone detection was achieved with minor responses (ΔG/G₀ < 1.4% at 500 ppm) toward interfering volatile organic compounds (VOC). analytes. We demonstrate a robust sensing platform using the polymer-SWCNT composites on a flexible PET substrate for potential application in wearable sensors.