A　novel　and　simple　oligodeoxyribonucleotide-based　sensor　with　single　fluorophore-labeled　for　mercury　ion　sensing　was　reported.　An　oligodeoxyribonucleotide　poly(dT)　was　labeled　with　fluorescein　as　donor.　Based　on　the　specific　binding　of　Hg(II)　to　T-T　mismatch　base　pairs,　the　formation　of　π-stacked　[T-Hg(II)-T]　with　＇sandwich＇　structure　on　the　addition　of　Hg(II)　ions　facilitates　the　electron　transfer　via　photoinduced　charge　transfer　(PCT),　which　creates　an　additional　nonradiative　decay　channel　for　excited　fluorophore　and　triggers　the　fluorescence　to　be　quenched.　The　π-stacked　[T-Hg(II)-T]　functioned　not　only　as　mercury　ion　recognition　but　also　as　an　electron　acceptor　to　quench　the　donor.　A　linear　relationship　was　observed　over　the　range　of　0-1.0　μM　with　the　detection　limit　of　20　nM　for　mercury　ions.　The　fluorescence　quenching　phenomenon　and　quenching　mechanism,　reliability　and　selectivity　of　the　system　were　investigated　in　detail.　©　2009　Elsevier　B.V.　All　rights　reserved.