An　impedimetric　method　is　described　for　ultrasensitive　analysis　of　mercury(II).　It　is　based　on　thymine-Hg(II)-thymine　interaction　which　causes　the　disintegration　of　multiple-sandwich　structured　DNA　chains.　DNA　strands　were　selected　that　are　partially　complementary　to　the　T-rich　Hg(II)-specific　oligonucleotides　(MSO).　They　were　immobilized　on　a　gold　electrode　via　Au-S　interaction.　Next,　the　MSO　and　the　bridging　strands　(BS)　that　can　connect　adjacent　MSOs　were　alternately　attached　through　layer-by-layer　hybridization.　Thus,　a　multiple-sandwich　structured　interface　in　created　that　carries　numerous　MSOs.　This　leads　to　a　change-transfer　resistance　(R-ct)　values　of　the　electrode-electrolyte　interface　at　faradic　electrochemical　impedance　spectroscopy　measurements　in　the　presence　of　the　hexacyanoferrate(II)/(III)　redox　probe　at　0.2　V　(vs.　Ag/AgCl).　If　Hg(II)　is　added　to　the　solution,　the　MSOs　selectively　interact　with　Hg(II)　to　produce　T-Hg(II)-T　structures.　Hence,　the　multiple-sandwich　hybridization　chains　become　disintegrated,　and　this　causes　a　decrease　in　resistivity.　The　effect　can　be　used　to　quantify　Hg(II)　over　an　analytical　range　that　extends　over　four　orders　of　magnitude　(1　fM　to　10　pM),　and　it　has　a　0.16　fM　limit　of　detection　under　optimal　conditions.