Full Paper Electrochemical Biosensing of DNA Immobilized Poly(Vinylferrocenium) Modified Electrode Filiz Kuralay , a Arzum Erdem, b * Serdar Abacı, a * Haluk Özyçrük, a Attila Yıldız a a Department of Chemistry, Faculty of Science, Hacettepe University, 06532 Beytepe-Ankara, Turkey b Department of Analytical Chemistry, Faculty of Pharmacy, Ege University, 35100 Bornova-Izmir, Turkey *e-mail: arzum.erdem@ege.edu.tr; sabaci@hacettepe.edu.tr Received: July 2, 2008 Accepted: September 18, 2008 Abstract The polymer, poly(vinylferrocenium) (PVF þ ) modified electrode was developed as the first time herein for the improved electrochemical sensing of DNA based on the oxidation signals of polymer and guanine. The morphologies of polymer film and DNA immobilized polymer film were examined using scanning electron microscope (SEM). The electrochemical behavior of polymer modified electrode was investigated by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in the absence/presence of DNA. Experimental parameters, such as the polymeric film thickness, the DNA immobilization time, the concentration of buffer solution, pH and DNA concentration were examined in order to obtain more sensitive and selective electrochemical signals. After optimization studies, DNA hybridization was also investigated. Keywords: Poly(vinylferrocenium) modified electrodes, Electrochemical DNA biosensor, Poly(vinylferrocene), Polymer, Guanine DOI: 10.1002/elan.200804361 1. Introduction DNA is the largest, naturally occuring, well defined molecule, that plays an important role in the life process [1]. Studies on the binding mechanism of some molecules with DNA have been identified as one of the key topics during the past few decades [2 – 5]. Electrochemical devices have received considerable attention in the development of DNA biosensors [6, 7]. The electrochemistry of DNA is irreversible and occurs at highly negative and positive potentials. Therefore, a derivative should be useful as a DNA probe that undergoes reversible electrode reactions at less-extreme potentials [8]. The electrochemical detection of binding of small molecules to DNA and generally DNA damage has been described in earlier reports [9 – 12]. The modification of nanoparticles with nucleic acids and their applications has attracted considerable attention in electro- chemistry [13]. The use of electroactive polymers as the transduction element of hybridization has been recently described in the literature. The characterization of poly(5-hydroxy-1,4- naphthoquinone) (juglone)-co-5-hydroxy-3-thioacetic acid-1,4-naphthoquinone) used for direct electrochemical detection of DNA hybridization has been reported by Piro et al. [14]. Pyrolytic graphite electrodes with adsorbed poly(4-vinylpyridine) (PVP) and attached Ru(bpy) 2þ 2 have facilitated reusable DNA biosensors [15]. Arora et al. reported DNA biosensor based on electrochemically de- posited polyaniline to detect complementary target, using oxidation of guanine and methylene blue [16]. Polypyrrole (PP) is one of the extensively used conducting polymers in design of bioanalytical sensors [17 – 21]. Poly-l-lysine/sin- gle-walled carbon nanotubes and electrochemically fabri- cated polyaniline nanowire-modified electrode has been also used for electrochemical DNA biosensor [22, 23]. Au nanoparticles (Au-NPs)-based protocol for DNA hybrid- ization detection based on assembly of alternating DNA and poly(dimethyldiallylammonium chloride) (PDDA) multi- layer films by electrostatic adsorption has been studied [24]. Positively charged chitosan (CS) and negatively charged DNA were alternately adsorbed on the surface of pyrolytic graphite electrodes [25]. The polyethyleneimine-copper(II) complex that could bind to DNA molecules mainly by electrostatic attraction were prepared by Kumar et al. [26]. Poly(vinylferrocenium) (PVF þ ) is a redox type polymer containing the ferrocene centers that are covalently bound to insoluble polymer skeleton. The polymer can be depos- ited onto the electrode surface by the electrooxidation of the reduced form poly(vinylferrocene) (PVF) by resulting a less soluble polymer [27, 28]. After the electrostatic immobili- zation of negatively charged biomolecules onto the polymer modified platinum (Pt) electrode effectively, it has been found that this polymer modified electrode can be used as a biosensor in order to monitor different molecules [28 – 38]. It is known that the PVF is a homegenous compact film whereas PVF þ is inhomogeneous film in which pores and pinholes exist [39, 40]. 2563 Electroanalysis 20, 2008, No. 23, 2563 – 2570  2008 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim