A　novel　label-free　electrochemical　sensor　has　been　developed　for　the　highly　sensitive　and　selective　detection　of　Hg2+.　Hg2+　were　first　captured　on　the　modified　electrode　surface　through　the　specific　thymine-Hg2+-thymine　(T-Hg2+-T)　coordination　and　then　through　the　catalytic　HAuCl4/NH2OH　reaction　for　the　formation　of　gold　nanoparticles　(AuNPs)　as　signal　reporter.　The　formed　AuNPs　could　be　directly　detected　by　stripping　voltammetry.　By　the　introduction　of　graphene　to　accelerate　electron　transfer　and　amplify　the　electrochemical　signal,　a　detection　limit　as　low　as　0.06　nM　could　be　obtained　for　Hg2+.　Compared　with　the　traditional　metal　nanoparticles　(NPs)-based　method,　this　sensor　avoids　the　labeling　of　the　DNA　probe　with　NP　tags,　only　one　unlabeled　T-rich　DNA　sequence　was　needed,　which　greatly　reduced　the　cost　and　simplified　the　sensing　procedure.　(C)　2014　Elsevier　B.V.　All　rights　reserved.