Rigid carbon composites: a new transducing material for label-free electrochemical genosensing

A rigid carbon-polymer composite material as a transducer for the electrochemical determination of label-free DNA based on differential pulse voltammetry (DPV) is reported. Graphite-epoxy composites (GEC) have an uneven surface allowing DNA, oligonucleotides and free DNA bases to be adsorbed using a simple and fast wet-adsorption procedure. In contrast with other transducers commonly used for electrochemical genosensing, the oxidation potentials are much lower when GEC is used. Free guanine base is oxidized at +0.35 V while adenine oxidation occurs at +0.63 V (vs Ag|AgCl). Cytosine and inosine free bases show no peaks within the experimental potential range. The oxidation of DNA guanine moieties occurs at a potential of +0.55 V while DNA adenine bases are oxidized at +0.85 V. A novel label-free hybridization genosensor using GEC as an electrochemical transducer for the specific detection of a sequence related with Salmonella spp. is also reported. This approach relies on the wet adsorption of the 23-mer inosine-substituted probe. The extent of hybridization onto the GEC surface between the probe and the target has been determined by using the oxidation signal of guanine coming from the target in connection with DPV. DNA hybridization has been determined in a target concentration of 10 mug/ml in 15 min of hybridization time. The hybridization event has also been detected in co-existing salmon testes DNA (stDNA) as interference. The features of this device are discussed and compared with state-of-the-art of label free DNA detection methods. (C) 2003 Elsevier B.V. All rights reserved.