Molecular wires as a new class of binders in carbon composite electrodes Afsaneh Safavi * , Norouz Maleki, Fatemeh Honarasa, Fariba Tajabadi Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran article info Article history: Received 13 January 2009 Received in revised form 6 March 2009 Accepted 17 March 2009 Available online 26 March 2009 Keywords: Carbon Molecular wire Diphenylacetylene Composite electrode abstract A new carbon composite electrode based on the use of a molecular wire as the binder is introduced. The composite electrode consists of graphite and diphenylacetylene (a molecular wire). The behavior of the electrode towards different categories of compounds such as FeðCNÞ 3=4 6 , Fe 3þ=2þ aq , dopamine, catechol, uric acid (UA) and ascorbic acid (AA) were tested. This novel electrode has conductivity similar to glassy carbon electrode (GCE). It shows large potential window, low background current and well defined vol- tammograms for the compounds tested. Another attractive feature of this electrode is its very high sta- bility in aqueous solutions. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Carbon paste electrodes (CPEs), due to their unique advantages, including chemical inertness, low cost, renewability, stable re- sponse, low background current and ease of modification have been used in many sensing and detection applications [1,2]. But CPEs suffer from several disadvantages such as low consistency and reproducibility as compared to the bare solid electrodes [3,4]. By modifying the electrode, the performance and stability can be improved. This is done by immobilizing the modifier on the surface of the electrode [5] or incorporation of the modifier into the bulk of the CPE [4]. Many efforts have been made to promote the performance of CPEs by alteration of the kind of binders. But the use of a conduct- ing binder has rarely been investigated [6]. Recently we introduced and characterized the electrochemical behavior of a new type of carbon composite electrode called carbon ionic liquid electrode (CILE) in which an ionic liquid, n-octyl pyridinium hexafluorophos- phate, has been used as a binder [6–9]. Classes of molecular entities that conduct electrical currents are called molecular wires (MWs). Phenyleneacetylene oligomers which have wire-like properties [10] are promising materials for a wide variety of applications in molecular electronic devices due to their ideal conductivity [11,12]. Diphenylacetylene (DPA) is the smallest conjugated oligomer and can be used as a conducting binder in CPEs. Very few reports have been published on using MW in carbon based electrodes [13,14]. Because of the lack of knowledge on the behavior of carbon pastes with electronic conductor binders, we studied the electro- chemical characteristics of a MW based carbon composite elec- trode. The results showed that the carbon MW electrode (CMWE) is very stable and shows satisfactory voltammetric characteristics. 2. Experimental Graphite powder (particle size <100 lm) and diphenylethane were from Fluka. Paraffin oil and DPA and other chemicals were obtained from Merck. Solutions with a concentration of 1 mM of AA, dopamine, cate- chol all in phosphate buffered saline(PBS) pH 7.0 solutions, 5 mM Fe 2+ in 0.1 M H 2 SO 4 (from Fe(NH 4 ) 2 (SO 4 ) 2  6H 2 O) and 1 mM FeðCNÞ 3=4 6 in 0.5 M KCl solution (from K 3 Fe(CN) 6 and K 4 Fe(CN) 6 ) were prepared. 1 mM UA was prepared by dissolving the solid in a small volume of 0.1 M NaOH solution and diluting to the desired concentration. Ultrapure water (q > 18 MX cm) was used for pre- paring all solutions. CPE and CMWE were prepared by hand-mixing a 70:30 (w/w) graphite powder to paraffin oil and graphite powder to DPA with different ratios (w/w), respectively. In the case of CMWE, the com- posite should be heated to a temperature higher than the melting point of DPA (m.p. = 62.5 °C). It was then left to cool to room tem- perature. A new surface was obtained by smoothing the electrode onto a weighing paper. An Autolab (Eco Chemie) electrochemical system equipped with GPES and FRA software was used. CPE, CMWE and GCE (all with 1.8-mm diameter) were used as working electrodes. The reference electrode was an Ag/AgCl/KCl (3 M) electrode while Pt was used as a counter electrode. Electrochemical impedance spectroscopy (EIS) 1388-2481/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2009.03.019 * Corresponding author. Tel.: +98 711 6137351; fax: +98 711 2286008. E-mail address: safavi@chem.susc.ac.ir (A. Safavi). Electrochemistry Communications 11 (2009) 1113–1115 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom