A　new　DNA　sensor　using　a　nickel(II)　phenanthroline　complex　([Ni(phen)(2)PHPIP]center　dot　2ClO(4))　as　the　electrochemical　probe　was　developed.　The　sensor　is　very　sensitive　and　selective　for　calf　thymus　DNA　(ctDNA)　detection　in　aqueous　medium.　The　Ni-phenanthroline　probe　was　synthesized　by　a　two-step　preparation　using　p-hydroxy-phenylimidazo-1,10-phenanthroline　(PHPIP)　as　the　ligand　and　characterized　with　IR,　UV　and　MS.　Some　interesting　electrochemical　properties　of　the　Ni-complex　and　the　interactions　of　the　complex　with　ctDNA　were　reported.　The　calculated　dynamics　parameters　of　the　electrode　process　indicate　that　there　are　obvious　interactions　between　the　probe　and　the　ctDNA　in　aqueous　solution.　Under　constant　potential　conditions,　the　redox　current　peak　of　the　probe　(Ni-complex)　decreases　obviously　as　the　probe　interacts/binds　with　ctDNAs.　This　unexpected　electrochemical　behavior　may　suggest　that　a　new　adduct　through　the　binding　of　Ni-phenanthroline　complex　with　ctDNA　is　formed　electrochemically.　By　estimation,　the　binding　ratio　of　the　probe　and　ctDNA　was　found　to　be　1:1　with　a　binding　constant　beta=4.29　x　10(5)　mol　L-1　in　aqueous　solution　at　room　temperature.　(C)　2010　Elsevier　B.V.　All　rights　reserved.