O 2 plasma-functionalized SWCNTs and PEDOT/PSS composite film assembled by dielectrophoresis for ultrasensitive trimethylamine gas sensor Xishan Guo, * a Jinming Jian, a Liwei Lin, b Hanyu Zhu a and Songming Zhu a A novel gas sensor based on composite films of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) and single-walled carbon nanotubes (SWCNTs) was fabricated for the detection of fishy trimethylamine (TMA) vapor. The SWCNTs were functionalized by O 2 plasma treatment to improve their solubility in the polymeric matrix, and alternative current dielectrophoresis was utilized for the first time to assemble the PEDOT/PSS–SWCNTs composite film to enhance the response to TMA molecules. The high resolution transmission electron microscopy (HR-TEM) images showed that the SWCNTs maintained their bulk structure after O 2 plasma functionalization. The scanning electron microscopy (SEM) images of the composite film showed that the oxidized SWCNTs were orderly arranged and uniformly dispersed into the polymer by dielectrophoresis. Compositional analyses of SWCNTs by X-ray photoelectron spectroscopy (XPS) suggested that O 2 plasma functionalization could remove amorphous carbon from the nanotube surface and introduce more hydrophilic oxygen-containing groups, leading to the improvement of SWCNTs solubility in the polymeric matrix. Gas sensitivities of the composite films largely relied on the treatment conditions. Compared to the raw or acid-treated SWCNTs-doped composite films, the film doped with SWCNTs modified by O 2 plasma at 30 W for 3 min exhibited the most sensitive and stable response characteristics to ppb-level TMA gas. 1 Introduction The combination of conducting polymers (CPs) having extended delocalised p-orbitals along the polymer backbone and single-walled carbon nanotubes (SWCNTs) with unique symmetric all-carbon structures, endows the conjugated systems (CPs–SWCNTs) with large surface areas for gas absorption and the ability to effectively transport the charge carriers which are generated in the interactions between gas molecules and sensing lms. 1–3 Hence, gas sensors based on the CPs–SWCNTs composite lms show sensitive responses to various gas species, in addition to other advantages such as good processability, high efficiency, and low power con- sumption. 4,5 In recent years, poly(3,4-ethylenedioxythiophene)/ poly(styrenesulfonate) (PEDOT/PSS) has been considered as a promising candidate for combination with nanotubes owing to its outstanding properties of high conductivity, chemical stability under ambient conditions, unique gas sensing response to polar gas molecules, and the surfactant- like nature for carbon nanotubes. 6–10 However, the weak solubility and random dispersion of SWCNTs in the polymeric matrix are still the main obstacles to the CPs–SWCNTs composites. 11 The solubility of SWCNTs is largely reduced by the self- agglomeration of nanotubes and the weak bonding to poly- mers. 12 Because of large specic surface areas, the inevitable self-agglomeration of SWCNTs leads to weak dispersion. The inactive outside layer of amorphous carbon on the intrinsic SWCNTs surface results in weak interfacial bonding between the nanotubes and the polymers. 13 Typically, these situations can be overcome by oxidative functionalization of nanotubes through attaching various oxygen-containing groups on the nanotube surfaces. 14,15 In addition, oxidizing treatments can alter the density of states of the nanotubes and improve the work function, leading to variation of the electronic properties of SWCNT bundles. 16,17 Compared with the conventional oxidative modication by strong acids which will detrimentally damage the structures of SWCNTs, the gentle and non-polluting O 2 plasma treatment could maintain the bulk properties of the nanotubes without much structural destruction. 18,19 It has been reported that O 2 plasma modication of CNTs strengthened the bonding between the nanotubes and polyaniline, and enhanced the response of the composite lm to NH 3 gas. 13 On the other hand, improving the random dispersion of CNTs in the polymer matrix has recently received much atten- tion, since the mechanical and electrical properties of polymer– CNTs composites are directly linked to the alignment of carbon a Department of Biosystems Engineering, Zhejiang University, Hangzhou 310058, China. E-mail: guoxs@zju.edu.cn; Fax: +86 571 8898 2373; Tel: +86 571 8898 2373 b Berkeley Sensor and Actuator Center, University of California at Berkeley, CA 94720- 1774, USA Cite this: Analyst, 2013, 138, 5265 Received 15th November 2012 Accepted 3rd June 2013 DOI: 10.1039/c3an36690a www.rsc.org/analyst This journal is ª The Royal Society of Chemistry 2013 Analyst, 2013, 138, 5265–5273 | 5265 Analyst PAPER Published on 03 June 2013. Downloaded by Zhejiang University on 02/10/2014 08:07:36. View Article Online View Journal | View Issue