Heavy　metal　ion　pollution　poses　severe　risks　in　human　health　and　environmental　pollutant,　because　of　the　likelihood　of　bioaccumulation　and　toxicity.　Driven　by　the　requirement　to　monitor　trace-level　mercury　ion　(Hg2+),　herein　we　construct　a　new　DNA-based　sensor　for　sensitive　electrochemical　monitoring　of　Hg2+　by　coupling　target-induced　formation　of　gold　amalgamation　on　DNA-based　sensing　platform　with　gold　amalgamation-catalyzed　cycling　signal　amplification　strategy.　The　sensor　was　simply　prepared　by　covalent　conjugation　of　aminated　poly-T(25)　oligonucleotide　onto　the　glassy　carbon　electrode　by　typical　carbodiimide　coupling.　Upon　introduction　of　target　analyte,　Hg2+　ion　was　intercalated　into　the　DNA　polyion　complex　membrane　based　on　T-Hg2+-T　coordination　chemistry.　The　chelated　Hg2+　ion　could　induce　the　formation　of　gold　amalgamation,　which　could　catalyze　the　p-nitrophenol　with　the　aid　of　NaBH4　and　Ru(NH3)63+　for　cycling　signal　amplification.　Experimental　results　indicated　that　the　electronic　signal　of　our　system　increased　with　the　increasing　Hg2+　level　in　the　sample,　and　has　a　detection　limit　of　0.02nM　with　a　dynamic　range　of　up　to　1000nM　Hg2+.　The　strategy　afforded　exquisite　selectivity　for　Hg2+　against　other　environmentally　related　metal　ions.　In　addition,　the　methodology　was　evaluated　for　the　analysis　of　Hg2+　in　spiked　tap-water　samples,　and　the　recovery　was　87.9-113.8%.　©　2013　Elsevier　B.V.