A　powerful　double-hairpin　molecular　beacon　(DHMB)　was　developed　for　cancer-related　KRAS　gene　detection　based　on　the　one-to-two　stoichiometry.　During　target　DNA　detection,　DHMB　can　execute　signal　transduction　even　if　no　any　exogenous　element　is　involved.　Unlike　the　conventional　molecular　beacon　based　on　the　one-to-one　interaction,　one　target　DNA　not　only　hybridizes　with　one　DHMB　and　opens　its　hairpin　but　also　promotes　the　interaction　between　two　DHMBs,　causing　the　separation　of　two　fluorophores　from　quenchers.　This　leads　to　an　enhanced　fluorescence　signal.　As　a　result,　the　target　KRAS　gene　is　able　to　be　detected　within　a　wide　dynamic　range　from　0.05　to　200　nM　with　the　detection　limit　of　50　pM,　indicating　a　dramatic　improvement　compared　with　traditional　molecular　beacons.　Moreover,　the　point　mutations　existing　in　target　DNAs　can　be　easily　screened.　The　potential　application　for　target　species　in　real　samples　was　indicated　by　the　analysis　of　PCR　amplicons　of　DNAs　from　the　DNA　extracted　from　SW620　cell.　Besides　becoming　a　promising　candidate　probe　for　molecular　biology　research　and　clinical　diagnosis　of　genetic　diseases,　the　DHMB　is　expected　to　provide　a　significant　insight　into　the　design　of　DNA　probe-based　homogenous　sensing　systems.