Genomagnetic assay based on label-free electrochemical detection using magneto-composite electrodes

A very sensitive genomagnetic assay based on a label-free electrochemical detection of the DNA target by using graphite-epoxy composite (GEC) and magneto-GEC electrodes as electrochemical transducers has been developed. The assay is based on the capture of DNA target on streptavidin magnetic beads by its hybridization with biotinylated inosine-substituted probe and its electrochemical detection achieved by the measurement of the signal coming from the guanine oxidation of the DNA target. The genomagnetic assay involves the following steps: the immobilization of biotinylated inosine-substituted capture probe onto streptavidin coated magnetic beads following by hybridization with its target DNA or in the presence of non-complementary (NC) DNA. Two different genomagnetic strategies have been developed for the selective electrochemical detection of DNA target. Firstly, an alkaline treatment was performed in order to dissociate DNA hybrids from the magnetic beads, followed by the voltammetric measurement of guanine oxidation signal using GEC electrode as an electrochemical transducer. In order to simplify the genomagnetic procedure, in the second strategy the magnetic separation was directly achieved by using a novel magneto-electrochemical transducer based on GEC electrode containing a small magnet (m-GEC). The genomagnetic assay based on label-free electrochemical detection was developed for the specific detection of a sequence related with Salmonella spp. with a target concentration of 20 mu g/mL in 20 min of hybridization time. The main features related with these genomagnetic assays, such as detection limit and the reproducibility, are discussed and compared with other genomagnetic assays. (c) 2005 Elsevier B.V. All rights reserved.