We report here a new strategy to graft both redox and DNA probes on carbon nanotubes to make a label-free DNA sensor. Oxidized single-walled carbon nanotubes are first immobilized on a self-assembled monolayer of cysteamine; then the redox probe, a quinone derivative 3-[(2-aminoethyl)sulfanyl-5-hydroxy-1,4-naphthoquinone], is grafted on the free carboxylic groups of the nanotubes. After that, for DNA probe grafting, new carboxylic sites are generated via an aryl diazonium route. After hybridization with a complementary sequence, the conformational changes of DNA could influence the redox kinetics of quinone, leading to a current increase of the redox signal, detected by square wave voltammetry. The system is selective, as it can discriminate a single mismatched sequence from the complementary one.