Herein,　we　describe　a　novel　trigger-induced　DNA　nanoassembly　method　using　only　one　loop-stem　shaped　hairpin　probe　(HP)　that　consists　of　three　different　functional　regions　as　a　single　building　unit.　The　Region　I　is　designed　complementary　to　the　trigger,　while　the　Region　II　and　Region　III　are　projected　to　complementary　with　each　other.　When　hybridized　with　the　trigger,　a　toehold　mediated　strand　displacement　(TMSD)　occurred　on　the　strand　of　Region　I,　leading　to　the　release　of　Region　III　for　further　hybridization　with　the　Region　II　on　another　HP　molecule　and　in　turn　inducing　a　stepwise　growth　of　HP　with　the　aid　of　polymerase.　Unlike　the　conventional　assembly　approaches　that　rely　on　the　sophisticated　sequence　design　and　complex　operation,　the　single-HP　nanoassembly　is　easy　and　fast.　Moreover,　because　many　HPs　are　opened　during　the　assembly　process,　we　exemplified　the　nanoassembly　strategy　by　re-designing　a　new　labeled　hairpin　probe　to　analyze　the　Kras　oncogene　With　a　high　sensitivity　and　specificity.　The　present　study　demonstrated　a　novel　promising　DNA　nanoassembly　strategy　for　biological　applications.