In this study, an electrochemical biosensor was developed for highly sensitive and specific detection of target miRNA-155. The structure was formed by the hybridization of a tetrahedral DNA nanostructure-based biomolecular probe assembled on 3D nitrogen-doped reduced graphene oxide/gold nanoparticles (3D N-doped rGO/AuNPs) electrode surface. Upon addition of target miRNA-155, the gold and silver nanorod/thionine/complementary DNA (AuAgNR/Thi/F) was hybridized with the target, and used for signal amplification, catalyzing the reduction of Thi as an electron mediator. Due to the signal amplification by the enhanced immobilization of DNA on the surface of 3D N-doped rGO/AuNPs electrode and AuAgNR/Thi, coupling the low background signal produced by blank solution, electrochemical performance of the device was optimized to be proportional to miRNA-155 concentration in the range of 1 x 10(-11) to 1 x 10(-4) M with a detection limit of 1 x 10(-12) M. In addition, direct detection in serum is demonstrated with high specificity. Thus, this biosensor is potentially applicable for microRNA detection in medical research and early clinical diagnosis.