Here we design an electrochemical DNA sensor, in which electrochemically active compound play a dual role - electrochemical indicator and anchor for probe DNA immobilization. [Co(phen)(2)(L-Cys)] (phen = 1,10-phenanthroline) was selected to play the dual roles, and was immobilized on gold electrode surface in two steps. The designed DNA sensor showed good selectivity, which can be used for one-base mismatch discrimination. Meanwhile, the peak intensity was linear with the logarithmic value of the complementary target DNA concentration from 1 pM to 1 mu M with a correlation coefficient of 0.99. (C) 201 2 Elsevier B.V. All rights reserved.