Electrical characterization of functionalized platinum electrodes and ISFET sensors for metal ion detection M. Ben Ali a,b, * , T. Homri c , Y. Korpan d , A. Abdelgani b , M. Ali Maaref b , L. Liu e , N. Jaffrezic-Renault e , C. Martelet e a Institut Supe ´rieur des Sciences Applique ´es et de la Technologie, 4003 Sousse, Tunisia b Laboratoire de Physique des Semiconducteurs et Capteurs, IPEST la Marsa, 2070 Tunis, Tunisia c Laboratoire de synthe `se organique et catalyse homoge `ne, Faculte ´ des Sciences de Monastir, 5000 Monastir, Tunisia d Institute of Molecular Biology and Genetics NAS, 150 Zabolotnogo str., 03143-UA, Kyiv-143, Ukraine e CEGELY, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, 69134 Ecully Cedex, France Available online 29 November 2005 Abstract This paper reports the application of functionalized platinum (Pt) electrodes and ChemFETs sensors for metal ion detection. The sensitive part of the sensors consists in a film of ethyl 2-thienylglyoxalate (ETGO) deposited by a spin-coating process. Electrochemical impedance spectroscopy was used to investigate the electrical properties of functionalized Pt electrodes. The optimized working conditions of the sensors have been studied with regard to the sensitivity performances, in particular, the polarization was adjusted to  0.85 V/ESC in order to neglect the Warburg effects at low frequencies. The functionalized Pt electrodes have shown a good sensitivity towards Cu(II) ions, whereas low response towards Ca(II) ions was observed. The ETGO/ISFET devices have shown good sensitivity (14 mV/decade) and linear responses over at least two decades of Cu(II) activity compared to (0.5 mV/decade) for Ca(II) ions. D 2005 Elsevier B.V. All rights reserved. Keywords: Platinum electrode; ChemFET; Impedance spectroscopy; Copper ion detection 1. Introduction The determination of heavy metals in the environment is of great interest since their dangerous effects on the ecosystem and human health depend on concentrations and relative toxicities. Copper is known as a necessary oligoelement for life, but on another side, is highly toxic to organisms as algae, fungi, bacteria or viruses [1]. Copper is suspected to cause infant liver damages. Drinking water can be a potential source for heavy copper intake. Sensing systems based on functionalized semiconductors and metallic electrodes transducers are quite attractive for the development of ion-sensitive sensors in aqueous solutions due to high sensitivity and selectivity, furthermore they are easy to be used [2–5]. Ion sensitive sensors are composed of a sensitive part including a specific ionophore deposited on a transducer. Several approaches can be used for the functionalization of these transducing surfaces. The sensing molecules can be fixed on conductive or insulating surfaces mainly through three methods: – Physisorption of the sublimated ionophore [6,7]; – Inclusion of the ionophore in the sensing membrane obtained by sol-gel processes [8]; – Chemisorption of the ionophore film obtained by spin- coating and dip-coating techniques followed by solvent evaporation [9]. The first two methods lead to good adhesion properties and thus to a promising way for preparation of ion-sensitive membranes [8]. In previous works [10–13], a large variety of organic sensing ionophores and polymeric compounds as sensitive membranes for ion detection were used. In particular, receptors 0928-4931/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.msec.2005.10.066 * Corresponding author. Institut Supe ´rieur des Sciences Applique ´es et de Technologie de Sousse, Ibn Khaldoun 4003 Sousse, Tunisie. Tel.: +216 73332656; fax: +216 73332658. E-mail address: mounirbenali@yahoo.fr (M. Ben Ali). Materials Science and Engineering C 26 (2006) 149 – 153 www.elsevier.com/locate/msec