Talanta 65 (2005) 888–894 Modification of carbon ceramic electrode prepared with sol–gel technique by a thin film of chlorogenic acid: application to amperometric detection of NADH Abdollah Salimi ∗ , Rahman Hallaj, Mohammad Ghadermazi a Department of Chemistry, Faculty of Science, Kurdistan University, P.O. Box 416, Sanandaj, Iran Received 16 March 2004; received in revised form 21 July 2004; accepted 12 August 2004 Available online 25 September 2004 Abstract The carbon ceramic electrode prepared with sol–gel technique is modified by a thin film of chlorogenic acid (CGA). By immersing the carbon ceramic electrode in aqueous solution of chlorogenic acid at less than 2 s a thin film of chlorogenic acid adsorbed strongly and irreversibly on the surface of electrode. The cyclic voltammetry of the resulting modified CCE prepared at optimum conditions shows a well-defined stable reversible redox couple due to hydroquinone/quinone system in both acidic and basic solutions. The modified electrode showed excellent electrocatalytic activity toward NADH oxidation and it also showed a high analytical performance for amperometric detection of NADH. The catalytic rate constant of the modified carbon ceramic electrode for the oxidation of NADH is determined by cyclic voltammetry measurement. Under the optimised conditions the calibration curve is linear in the concentration range 1–120 m. The detection limit (S/N = 3) and sensitivity are 0.2 M and 25 nA M -1 .The results of six successive measurement-regeneration cycles show relative standard deviations of 2.5% for electrolyte solution containing 1mM NADH, indicating that the electrode renewal gives a good reproducible and antifouling surface. The advantages of this amperometric detector are: high sensitivity, excellent catalytic activity, short response time t < 2 s, remarkable long-term stability, simplicity of preparation at short time and good reproducibility. © 2004 Elsevier B.V. All rights reserved. Keywords: Carbon ceramic electrode; Sol–gel; Chlorogenic acid; NADH; Amperometry 1. Introduction Sol–gel technology has been used to prepare inorganic and organic–inorganic composite films through the hydrol- ysis and condensation of metal alkoxides, most notably the silicon alkoxides [1–3]. These materials are now being devel- oped for use in chromatographic separations [4,5], full cells [6] and as supports for optical sensors [7,8]. Considerable re- search efforts are constantly being devoted to development of chemical sensors and biosensors based on sol–gel technology [9–13]. Due to the inert low temperature process, the sol–gel method provides an attractive way for the immobilization of heat-sensitive biological entitles (enzyme, protein and anti- ∗ Corresponding author. Tel.: +98 8716624862; fax: +98 8716660066. E-mail address: absalimi@yahoo.com (A. Salimi). body). This class of sol–gel silicate matrix possesses chemi- cal inertness, physical rigidity, negligible swelling in aqueous solutions, tenable porosity, high photochemical and thermal stability and optical transparency. These attractive features have led to an intensive research in the optical and electro- chemical sensors and biosensors. Sol–gel electrochemistry has been rapidly developed over the last 5 years and has become an area of active research [11,14–16]. The sol–gel technique is a new, simple and renewable method for the preparation of the modified electrodes and solid electrolytes [11]. Since the pioneering work of Lev’s group [17,18] on ce- ramic carbon composite electrodes (CCEs) much effort has been devoted to the fabrication of chemically modified CCEs and using them as sensor for amperometric and voltammet- ric detection of analytes. The chemical modifications of inert substrate electrodes with redox active thin films offer signif- 0039-9140/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2004.08.010