We　propose　a　DNA　nanomachine　(simplified　as　MB-PP)　by　inserting　molecular　beacon　into　a　padlock　probe　for　the　sensitive　and　specific　detection　of　K-ras　gene　mutation.　In　the　presence　of　target　DNA,　MB-PP　is　able　to　be　cyclized　by　ligase　because　its　two　ends　are　pulled　together　by　target　species.　In　this　case,　rolling　circle　amplification　(RCA)　occurs　via　the　extension　of　primer　by　polymerase　on　cyclized　MB-PP(CMB-PP),　and　thus　two　complete　binding　sites　of　nicking　endonuclease　are　obtained　due　to　the　formation　of　RCA　product/CMB-PP　duplex.　Naturally,　a　steady　stream　of　two　types　of　nicked　fragments　flow　out　from　continuous　rolling　CMB-PP　nanomachine　after　introduction　of　nickase,　one　of　which　can　in　turn　triggers　strand-displacement　amplification　(SDA),　leading　to　the　dramatic　accumulation　of　nicked　fragments.　As　a　result,　even　in　the　presence　of　a　trace　amount　of　wild　target　DNA,　the　fluorescence　intensity　will　substantially　increase.　Utilizing　this　DNA　machine,　the　K-ras　gene　can　be　detected　down　to　50　pM　with　the　linear　response　range　from　50　pM　to　10　nM.　Moreover,　the　point　mutation　existing　in　the　codon　12　of　K-ras　can　be　easily　distinguished　from　the　wild　type.　(C)　2017　Elsevier　B.　V.　All　rights　reserved.