Sensors and Actuators B 185 (2013) 478–487 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journal h om epage: www.elsevier.com/ locate/snb A solid-state sensor based on tris(2,2 ′ -bipyridyl)ruthenium(II)/poly(4-aminodiphenylamine) modified electrode: Characterization and applications Emad A. Khudaish a,∗ , Mohammed M. Al-Hinaai a , Salim H. Al-Harthi b a Sultan Qaboos University, College of Science, Department of Chemistry, PO Box 36, PC 123, Muscat, Oman b Sultan Qaboos University, College of Science, Department of Physics, PO Box 36, PC 123, Muscat, Oman a r t i c l e i n f o Article history: Received 2 February 2013 Received in revised form 1 May 2013 Accepted 6 May 2013 Available online xxx Keywords: Electropolymerization 4-Aminodiphenylamine Tris(2,2 ′ -bipyridyl)ruthenium(II) Heavy metals a b s t r a c t A solid-state sensor based on poly(4-aminodiphenylamine) film deposited at glassy carbon electrode doped with tris(2,2 ′ -bipyridyl)Ru(II) complex (Padpa/Ru/GCE) was constructed electrochemically. The surface morphology of the film modified electrode was characterized using electrochemical and surface scanning techniques. A redox property represented by [Ru(bpy) 3 ] 3+/2+ couple immobilized at the Padpa moiety was characterized using typical voltammetric techniques. The XPS data demonstrated the exist- ence of ( N ) bonding responsible for polymer formation while the degree of polymerization is reduced by the presence of components containing chloride ions, specifically ( NH 3 + Cl - ) which is expected to rule the linkage of Padpa with Ru-complexes. The AFM image reveals a broken and fused Padpa/Ru fiber structure compared to a relatively uniform Padpa film. Parameters such as electron transfer coefficient, surface concentration, roughness and energy dissipation were estimated. Primarily, the modified elec- trode was applied as an environmental sensor for the simultaneous determination of Zn 2+ , Cd 2+ , Pb 2+ and Cu 2+ ions in water samples. The detection limits for these metal ions were dropped to 122.5, 21.7, 9.8 and 28.0 ppb, respectively. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Heavy metals are natural components of the Earth’s crust char- acterized by their relatively high density and at certain levels are hazardous for aquatic ecosystem and human health [1,2]. Owing to the huge developments of industry, waste contains heavy metals have been increased sharply regardless of different methods of treatment employed to reduce their waste disposal [3]. However, the levels of toxic metals disposed into water bodies are still rising, mainly in aqueous effluents discharged into ground and sea waters [4]. Consequently, the determination of potential toxic metals in environmental samples becomes one of main important issues in extensive researches. Several analytical methods such as atomic absorption spectrometry [5], inductively coupled plasma with mass spectrometry [6] as well as electrochemistry [7], have been devel- oped for these purposes. Desirable characteristics of a portable metal analyzer include efficiency, reproducibility and precision, robustness, simply to fabricate and operate with minimal regen- eration of sensors [8–11]. The development of electrochemical methods, namely the stripping voltammetry, for detecting heavy ∗ Corresponding author. Tel.: +968 2414 1474; fax: +968 2414 1469. E-mail address: ejoudi@squ.edu.om (E.A. Khudaish). metals has attracted considerable attention due to its potential high sensitivity and reproducibility for measurements of many danger- ous pollutants [12]. For this task, many efforts were devoted to modify the surface sensing materials by attachment of organic or inorganic substances including a mercury film [13,14], bismuth film [15,16], antimony film [17], self assembled monolayer (SAM) and conducting polymers (CP) [18–20]. Mercury electrodes (drop or film coated) are unique surfaces for quantification of heavy metals due to their high reproducibility and remarkable low detection limits. Although they are attrac- tive adsorption and catalytic surfaces but their applications for environmental monitoring were declined due to environmental impact. Therefore, intensive researches were directed and focused in construction of chemically modified electrodes (CME) for several applications including environmental monitoring. Due to their interesting electrical and optical properties, conducting polymers have concerned much interest recently in the development of sensors [21,22]. For example polyani- line modified quartz crystal electrode was used to determined Cr(VI) [23], poly(3-methylthiophene) modified gold electrode was applied to detect Hg(II) [11], polypyrrole membranes were deposited on glassy carbon to determined silver [9], and poly(3,4- ethylenedioxythiophene) modified electrode was used to detect five heavy metals [19]. Also, the polythiophene modified glassy 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.05.017