CO Sensor Bull. Korean Chem. Soc. 2013, Vol. 34, No. 8 2291 http://dx.doi.org/10.5012/bkcs.2013.34.8.2291 Carbon Monoxide Sensor Based on a B2HDDT-doped PEDOT:PSS Layer R. Memarzadeh, †,#,a Hui-Bog Noh, #,a S. Javadpour, †,* F. Panahi, ‡ A. Feizpour, § and Yoon-Bo Shim #,* † Department of Materials Science & Engineering, Shiraz University, Shiraz, Iran. * E-mail: sirus.javadpour@gmail.com ‡ Department of Chemistry, College of Sciences, Shiraz University, Shiraz, Iran § Department of Chemistry and the Photonics Center, Boston University, Boston, Massachusetts 02215, U.S.A. # Department of Chemistry and Institute of BioPhysio Sensor Technology, Pusan National University, Busan 609-735, Korea * E-mail: ybshim@pusan.ac.kr Received April 24, 2013, Accepted May 7, 2013 An efficient carbon monoxide (CO) sensor was developed based on poly(3,4-ethylenedioxy)thiophene- poly(styrenesulfonate) (PEDOT:PSS) modified with a new pyrimidine-fused heterocyclic compound, bis(2- hydroxyphenyl)dihydropyrido[2,3-d:6,5-d]dipyrimidine-tetraone (B2HDDT). B2HDDT remains stable in the polymer matrix through interactions with functional groups of the polymer. It created prominent sites that captured CO gas, and the experimental parameters, including the amount of doped B2HDDT in the PEDOT:PSS film, were optimized. The sensor probe was also examined to verify its reliability for detecting CO in the presence of atmospheric gases in a discriminating manner. NMR, AFM, and FT-IR spectra were obtained to evaluate the structure and morphology of the B2HDDT-doped PEDOT:PSS (PEDOT:PSS/ B2HDDT) film. The content of 35 vol % B2HDDT (7.0 mM) in PEDOT:PSS provided the largest response factor (ΔR/Ro) for the CO gas. The sensor response was reproducible, with a relative standard deviation < 5% (n = 5). The detection limit was determined to be 0.44 ± 0.05 vol %. Key Words : PEDOT:PSS, Gas sensor, Carbon monoxide, Conductive polymer Introduction Carbon monoxide (CO) is an odorless and colorless gas, which makes it a well-known silent killer. Monitoring of the CO concentration in air is therefore necessary. The conv- entional materials used for CO sensors are semiconducting metal oxides, solid electrolytes, and ionic membranes. In addition to these materials, conducting polymers have been used for this application. 1 Until now, polyanilines, poly- pyrroles, polythiophenes, and their derivatives have been successfully used for CO sensing. They have the advantages of low cost, low temperature requirements, and ease of fabrication compared with other materials used to detect CO. Moreover, conducting polymers have other desirable proper- ties, such as piezoresistivity, spectral sensitivity (an increase in resistance under irradiation by photons of different wave- lengths), and thermistors properties. 2 Among the conducting polymers, poly(3,4-ethylenedi- oxy)thiophene (PEDOT) composite is one of the materials used for sensor fabrication. Dispersion of PEDOT and poly- (styrenesulfonate) (PSS) in water has been used in diverse sensor applications in recent years. 3 In addition, PEDOT: PSS has also been doped with other compounds, such as dimethyl sulfoxide, tetrahydrofuran (THF), sorbitol, 2-nitro- ethanol, methyl sulfoxide, polyethylene glycol, and ethylene glycol, to increase its conductivity (100-fold in some cases), which can change the sensing properties of the polymers. 4 This strategy has also been utilized to great benefit in the biomedical field for biosensing and drug delivery appli- cations. 5 A PEDOT:PSS/nanotube composite has been used in a controlled drug release system. 6 PEDOT:PSS/Au nano- composites and inkjet-printed PEDOT:PSS have been used as new transducers with enzyme immobilization in ampero- metric glucose biosensors. 7 PEDOT:PSS has recently attract- ed significant attention for its applications in gas sensors: PEDOT:PSS nanocomposites, PEDOT:PSS/Pd and PEDOT: PSS/polyvinylpyrrolidone, were used as sensors for chemical vapors (ethanol, methanol, THF, and acetone) and NO and NH 3 gases. 8 The inclusion of dopant molecules into a con- ductive polymer is beneficial to sensor performance. For example, a metal complex and morphline were used as dopants for detection of CO. 9 Thus, we have investigated new dopant molecules to enhance sensor performance. In the present study, an efficient PEDOT:PSS-based CO sensor was studied through modification of PEDOT:PSS with a new pyrimidine-fused heterocyclic compound, bis(2- hydroxyphenyl)dihydropyrido[2,3-d:6,5-d]dipyrimidine-tetra- one (B2HDDT). This doping molecular dopant contains numerous functional groups that produce hydrogen bonds with target molecules and with the polymer matrix. 10 There- fore, this compound can be used as a dopant in PEDOT:PSS to improve the properties of the polymer for CO detection. Hence, B2HDDT-doped PEDOT:PSS was investigated for its ability to detect CO in the atmosphere. Experimental Materials and Interdigitate Electrodes. Chemicals were a These authors contributed equally to this work.