A　simple,　cost-efficient,　sensitive　and　selective　fluorescence　sensor　is　developed　for　sequence-specific　recognition　of　duplex　DNA　(ds-DNA)　in　vitro　using　metal-organic　framework　(MOF)　as　the　sensing　platform.　N,N-Bis(2-hydroxy-ethyl)　dithiooxamidatocopper((II))　(H(2)dtoaCu)　was　chosen　as　the　example　MOF,　because　it　strongly　chemisorbs　the　dye-labeled　probe　TFO　(triplex-forming　oligonucleotide),　and　quenches　fluorescence　from　the　dye.　In　the　presence　of　target　ds-DNA　(the　PPT　of　HIV　RNA,　a　16-bp　ds-DNA　sequence),　the　TFO　could　interact　with　the　major　groove　in　ds-DNA　(via　Hoogsteen　hydrogen　bonding)　to　form　a　rigid　triplex　structure,　resulting　in　fluorescence　recovery.　The　enhanced　fluorescence　signal　has　a　relationship　with　the　ds-DNA　concentration,　the　detection　limit　is　as　low　as　1.3　nmol　L-1　(S/N　=　3)　with　good　selectivity,　which　is　lower　than　that　based　on　a　graphene　oxide　platform　and　electrochemical-DNA　sensor.