ORIGINAL PAPER Andrea Kelley Æ Brian Angolia Æ Isam Marawi Electrocatalytic activity of poly(3-methylthiophene) electrodes Received: 14 September 2004 / Revised: 8 April 2005 / Accepted: 25 May 2005 / Published online: 19 July 2005 Ó Springer-Verlag 2005 Abstract Poly 3-methylthiophene (P3MT) modified electrodes have shown an improvement for detecting catecholamines when compared to classical ones. Past work with this polymer electrode suggested the possible presence of ‘‘active sites,’’ which are believed to be the polymer’s center of electrocatalytic activity. The inter- action of 1,5-anthroquinone-disolfonic acid (1,5-AQDS) at the P3MT electrode showed a nonreversible behavior resulting in the blocking of ‘‘the active sites,’’ suggesting the specific electcatalytical activity of this polymer is limited to catechol and similar compounds. In order to improve catecholamine detection, two methods of elec- tropolymerization for P3MT were compared under similar conditions; (1) a constant potential for a specific length of time, and (2) potential cycling. It was found that cycling provided a more sensitive CV, i.e. increased number of active sites. Under a controlled pH study (pH range 2–9), the polymer electrode maintained its supe- rior performance, manifested as lower DE and higher i, toward catechol over the traditional electrodes. Two different supporting electrolytes were used, sulfate and phosphate, and it was found that in neutral or basic solutions containing phosphate, the oxidation and reduction potentials of catechol shifted to lower values. Solutions containing sulfate exhibited no shift in the oxidation potential at any pH value. Keywords Poly-3-methylthiophene Æ Conducting polymer electrode Æ Supporting electrolytes Æ Cyclic voltammetry Æ Anthraquinone Æ Catecholamine Introduction Cyclic voltammetry (CV) studies of catecholamines (a class of neurotransmitters) at poly(3-methylthiophene) (P3MT) modified electrodes showed unusual character- istics and properties compared to commonly used elec- trodes, such as Pt, Au, glassy carbon, and chemically modified electrodes [1–6]. P3MT exhibited improved electrochemical reversibility, sensitivity, and selectivity toward catechol(s), nicotineamide adenine dinucleotide (NADH), and other molecules of biological importance over the traditional electrode materials [6]. Further, the polymer is easily deposited on the substrate surface and is found to be chemically and mechanically stable. P3MT has been shown to eliminate the issues of adsorption fouling and passivation of electrode surface by large molecules or oxidative products that are so often encountered when using conventional electrodes in biological fluids. Wang and Li [7] reported that vol- tammograms of 2·10 4 M chlorophenol showed com- plete fouling of the working glassy carbon electrode within four cycles. However, when P3MT was used, a highly reproducible current peak was observed with no surface fouling after repeated cycles. They also reported improved catecholamine detection under flow injection and liquid chromatography conditions [7]. Other stud- ies, based on diffusion coefficient measurements, have suggested that the electron transfer reaction of the cat- echol(s), NADH and ascorbic acid at P3MT film elec- trodes takes place at the organic surface/solution interface [8, 9]. Past research has shown that the electroactivity of the polymer can be changed when an electrochemically active molecule is incorporated into its matrix structure [10, 11]. Galal et al. [10] reported that when P3MT was polymerized in the presence of a ferrocene moiety, the activity of the polymer was enhanced, but the general structure of the polymer remained unchanged. They explained this behavior in terms of a lack of com- plexation of the ferrocene with the polymer backbone, A. Kelley Æ B. Angolia Æ I. Marawi (&) Chemistry Department, Xavier University, 3800 Victory Parkway, Cincinnati, OH, 45207-4221, USA E-mail: Marawi@xavier.edu Tel.: +1-513-7452064 Fax: +1-513-7453695 J Solid State Electrochem (2006) 10: 397–404 DOI 10.1007/s10008-005-0032-8