Full Paper DNA Biosensor Based on Carbon Paste Electrodes Modified by Polymer Multilayer AndreaK.Ioannou, a AnastasiaA.Pantazaki, b StellaTH.Girousi, a Marie-Claude Millot, c ClaireVidal-Madjar, c AnastasiosN.Voulgaropoulos a * a Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, 54124Thessaloniki, Greece b Laboratory of Biochemistry, Department of Chemistry, Aristotle University of Thessaloniki, 54124Thessaloniki, Greece c Laboratoire de Recherche sur les Polyme `res, CNRS-Universite ´ Paris 12, 2-8 rue Henri Dunant, 94320 Thiais, France *e-mail: voulgaro@chem.auth.gr Received: October 21, 2005 Accepted: December 5, 2005 Abstract An electrochemical DNA biosensor was developed by DNA immobilization at the electrode surface and its electrochemical behavior was studied in relation with different materials added in the paste. The aim was to study new materials for the development of new electrode surfaces, to be applied in the study of DNA – drug interactions. New electrochemical sensing materials using polymer multilayers were reported for the adsorption of DNA. These materials were prepared by mixing a polymer ion exchanger and graphite powder. The mixture was then used to render the modified carbon paste electrode (CPE), on the surface of which the dsDNA was adsorbed and studied by differential pulse voltammetry (DP voltammetry). The signal of guanine oxidation peak of DNA was followed. This modified biosensor was applied for the study of the interaction between DNA and the known intercalators Ethidium Bromide (EB) and Acridine Orange (AO). The established biosensor exhibited an improvement of its sensitivity and repeatability compared with the conventional CPE DNA biosensor. Keywords: DNA biosensor, Guanine, Polymers, Voltammetry, Electroanalysis DOI: 10.1002/elan.200503421 1. Introduction Different analytical methods are developed for the detec- tion of DNA damage and/or its interactions with various molecules, including fluorescence [1–4], surface plasmon resonance [5, 6], quartz crystal microbalance [7, 8], and electrochemistry. Applications of electrochemical tech- niques in DNA biosensor technology nowadays represent a dynamically developing field (reviewed in [9–16]). The advantagesoftheelectrochemicaltechniquesare:relatively lowcost,lowpowerrequirementsandportabilityofelectro- analytical devices. These devices, working as DNA hybrid- ization or DNA damage sensors, are available for routine medicaldiagnosisandforenvironmentalanalysis.Screening of the environment (water, air, food, workplace, etc.) for DNA damaging pollutants, monitoring of the level of oxidative DNA damage, together with detection of muta- tions in selected human genes (e.g., tumor suppressor p53 [17]), belong to important steps in prevention and early diagnosis of serious diseases, including cancer. Several reviews are available on electrochemical biosensors for DNA hybridization [9–11, 13, 16] and on applications of DNA modified electrodes as sensors for the detection of drugs or potential DNA-damaging agents [9–11, 13–15]. Inadditiontotheconventionalmethodsbasedonentrap- ment and adsorption of the biomolecule, many other procedures (cross-linking, covalent binding, molecular self-assembly) and new interfaces such as carbon paste polymer or copolymer films, screen-printed films and bulk- modified sol–gel matrices, have been developed to immo- bilize biomolecules [18–23]. Each method has its own advantages and disadvantages in terms of sensitivity, repeatability, cost, and keeping the activity of the biomo- lecule. However, the stable immobilization of macromolec- ular biomolecules on conductive microsurfaces with com- pleteretentionoftheirbiologicalrecognitionpropertiesisa crucial problem for the commercial development of mini- aturized biosensors. Effectively, most of the conventional procedures of biomolecule immobilization such as cross- linking, covalent binding and entrapment in gels or mem- branessufferfromalowreproducibilityandapoorspatially controlled deposition [24]. Rapid growth in biomaterials, especially the availability andapplicationofawiderangeofpolymersandcopolymers associated with new sensing techniques have led to remark- ableinnovationinthedesignandconstructionofbiosensors, significant improvements in sensor response and the emer- gence of new types of biosensors. Carbon-based materials suchasgraphite,carbonblackandcarbonfiberarealsoused to construct the conductive phase. These materials have a high chemical inertness and provide a wide range of anode working potentials with low electrical resistivity. They also 456 Electroanalysis 18, 2006, No.5, 456–464 # 2006 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim