A novel electrochemical biosensor for sensitive and selective DNA detection was constructed based on polydopamine@graphene composite functionalized with silver nanoparticles (AgNPs-Pdop@Gr). The Pdop@Gr was prepared by simple chemical route and AgNPs further deposited over the Pdop@Gr by mildly stirring to form AgNPs-Pdop@Gr composite films, which was considered as potential sensing platform. DNA labeled at 5' end using 6-mercapto-1-hexhane (HS-ssDNA) was immobilized on AgNPs-Pdop@Gr surface to form ssDNA-S-AgNPs-Pdop@Gr and hybridization sensing was done in phosphate buffer. Differential pulse voltammetry was applied to monitor the DNA hybridization event using methylene blue as an electrochemical indicator. Under optimum conditions, the peak currents of methylene blue were linear with the logarithm of the concentrations of complementary DNA from 1.0 x 10(-13) to 1.0 x 10(-8) M with a detection limit of 3.2 x 10(-15) M (3 sigma/S). The biosensor also displayed high selectivity to differentiate one-base mismatched DNA. All these excellent performances of the developed biosensor indicated that this sensing platform could be easily extended to the detection of other nucleic acids. (C) 2013 Elsevier Ltd. All rights reserved.