| Summary: | Multi-walled carbon nanotubes (MWCNTs) were grown on a stainless-steel foil by thermal chemical vapor deposition (CVD) process. The MWCNTs were functionalized with carboxylic groups (COOH) on their surfaces by using oxidation and acid (3:1 H<sub>2</sub>SO<sub>4</sub>/HNO<sub>3</sub>) treatments for improving the solubility property of them in the solvent. The functionalized MWCNTs (<i>f</i>-MWCNTs) were conducted to prepare the solution by continuous stir in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), dimethyl sulfoxide (DMSO), ethylene glycol (EG) and Triton X-100. The solution was deposited onto a bendable substrate such as polyethylene terephthalate (PET) with a fabricated silver interdigitated electrode for application in a room-temperature gas sensor. A homemade-doctor blade coater, an UNO R3 Arduino board and a L298N motor driver are presented as a suitable system for screen printing the solution onto the gas-sensing substrates. The different contents of <i>f</i>-MWCNTs embedded in PEDOT:PSS were compared in the gas response to ammonia (NH<sub>3</sub>), ethanol (C<sub>2</sub>H<sub>5</sub>OH), benzene (C<sub>6</sub>H<sub>6</sub>), and acetone (C<sub>3</sub>H<sub>6</sub>O) vapors. The results demonstrate that the 3.0% <i>v</i>/<i>v</i> of <i>f</i>-MWCNT solution dissolved in 87.8% <i>v/v</i> of PEDOT:PSS, 5.4% <i>v</i>/<i>v</i> of DMSO, 3.6% <i>v</i>/<i>v</i> of EG and 0.2% <i>v</i>/<i>v</i> of Triton X-100 shows the highest response to 80 ppm NH<sub>3</sub>. Finally, the reduction in the NH<sub>3</sub> response under heavy substrate-bending is also discussed.
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