This paper reported an ultrasensitive and label-free electrochemical DNA biosensing platform based on a newly synthesized water-soluble electroactive dye azophloxine-functionalized graphene nanosheets (AP-GNs). Azophloxine can be attached on the graphene surface through synergistic noncovalent chargetransfer and pi-pi stacking interactions with graphene. The attachment of azophloxine on the graphene surface not only acts as a stabilizer for graphene but also as the in situ probe for the electrochemical DNA detection. Under optimum conditions, this biosensor exhibited high sensitivity and low detection limit for detecting DNA. The linear range is from 1.0 x 10(-15) to 1.0 x 10(-11) mol L-1 and the detection limit is 4.0 x 10(-16) mol L-1. Furthermore, this biosensor showed extraordinary capability for single nucleotide polymorphisms (SNPs) assay. The results demonstrate that this AP-GNs based biosensor has potential application in sensitive and selective DNA detection. (C) 2013 Elsevier Ltd. All rights reserved.