The present manuscript describes an electrochemical assay for detection of different types of single base mismatches (SBM) using 3,4-diaminobenzoic acid (DABA) as a new redox reporter. DABA is covalently attached to DNA, and its electrochemical response is followed. The present assay can overcome to two main problems of the hybridization biosensors, direct electron transfer of the redox reporter with the electrode surface and the positioning of the reporter before mismatch position. The introduced biosensor is able to discriminate complementary target and the targets including a single base mismatch even thermodynamically stable ones such as G-A and G-T. (C) 2011 Elsevier Ltd. All rights reserved.