Talanta 72 (2007) 532–538 Synthesis and characterization of p-toluenesulfonate incorporated poly(3,4-ethylenedioxythiophene) Yinghong Xiao a,b,c , Chang Ming Li a,b,∗ , Shucong Yu a , Qin Zhou a,b , Vee. S. Lee d , Shabbir. M. Moochhala d a School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore b Center for Advanced Bionanosystems, Nanyang Technological University, Singapore 637457, Singapore c School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210014, China d Defence Medical & Environmental Research Institute, DSO National Laboratories, Singapore 117510, Singapore Received 30 October 2006; received in revised form 8 November 2006; accepted 8 November 2006 Available online 8 December 2006 Abstract Poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, was electrochemically synthesized with p-toluenesulfonate (TSNa) as a dopant on gold surface. The electrochemical properties of the polymer were studied by impedance spectroscopy and cyclic voltammetry (CV). It was found that the impedance magnitude of the electrode significantly decreased over a wide range of frequency from 10 0 to 10 4 Hz after the polymer deposition. The CV demonstrated enhanced reversibility of the PEDOT film. The surface morphology was investigated by scanning electronic microscope (SEM) and atomic force microscope (AFM). Due to the effect of TSNa structure, nano-fungus was observed. Polymerization time was optimized and 30 min deposition resulted in the highest charge capacity, showing the highest electroactive surface area, possibly due to its porous structured polymer. Moreover, the high specific surface area could be favorable for cell attachment. The stability of PEDOT in glutathione (GSH), a common biologically relevant reducing agent, was studied with polypyrrole (PPy) as a baseline. It showed that the former had much better stability than the latter and it could be an excellent candidate for potential applications of in vivo neural devices. © 2006 Elsevier B.V. All rights reserved. Keywords: PEDOT; Electrochemical properties; Surface morphology; Stability against reducing agents 1. Introduction Since the highly conductive polyacetylene was discovered in the late 1970s [1], conducting polymers have been inten- sively studied and successfully used in various areas such as sensors and actuators [2–4], batteries [5], antistatic coatings for photographic films [6], processing of electronic circuit boards [7]. Conducting polymers show interesting chemical and physical properties derived from their unique conjugated -electron system [8]. Amongst these polymers, polypyrrole (PPy) is often chosen for biological applications due to its ease of preparation, good conductivity and biocompatibility [9–11]. PPy was applied to modify implantable devices for neural recording and drug delivery [12,13]. However, applications of ∗ Corresponding author. Tel.: +65 67904485; fax: +65 67911761. E-mail address: ecmli@ntu.edu.sg (C.M. Li). PPy suffer from its instability in biological environment due to its structural disorder. Oxidized PPy is particularly unstable in biologically relevant reducing agents such as dithiothreitol (DTT) and glutathione (GSH). It is apparently disadvantageous to PPy modified electrodes which are implanted in brain tissues for long term use. Thiophene is difficult to polymerize electrochemically due to its high oxidation potential in aqueous media [14]. Recently a derivative of polythiophene, poly(3,4- ethylenedioxythiophene) (PEDOT), which could be easily electrochemically synthesized has aroused great interest of material scientists. PEDOT has been classified as a low band gap conducting polymer. The 3,4-dioxy substitution pattern blocks the possibility of -( ′ ) coupling normally presented in PPy (Scheme 1, left), which can result in a more regiochemically defined material (Scheme 1, right), adds electron density to the aromatic heterocycle, and reduces the monomer oxidation potential. Its high thermal stability has been reported [15]. Addi- tionally, the decrease of the polymer reduction potential would 0039-9140/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2006.11.017