K-Ras　mutations　at　codon　12　play　an　important　role　in　an　early　step　of　carcinogenesis.　Here,　a　label-free　colorimetric　isothermal　cascade　amplification　for　ultrasensitive　and　specific　detection　of　K-Ras　point　mutation　is　developed　based　on　a　double-hairpin　molecular　beacon　(DHMB).　The　biosensor　consists　of　DHMB　probe　and　a　primer-incorporated　polymerization　template　(PPT)　designed　partly　complementary　to　DHMB.　In　the　presence　of　polymerase,　target　DNA　is　designed　to　trigger　strand　displacement　amplification　(SDA)　via　promote　the　hybridization　of　PPT　with　DHMB　and　subsequently　initiates　cascade　amplification　process　with　the　help　of　the　nicking　endonuclease.　During　the　hybridization　and　enzymatic　reaction,　G-quadruplex/hemin　DNAzymes　are　generated,　catalyzing　the　oxidation　of　ABTS(2-)　by　H2O2　in　the　presence　of　hemin.　Utilizing　the　proposed　facile　colorimetric　scheme,　the　target　DNA　can　be　quantified　down　to　4　pM　with　the　dynamic　response　range　of　5　orders　of　magnitude,　indicating　the　substantially　improved　detection　capability.　Even　more　strikingly,　point　mutation　in　K-ras　gene　can　be　readily　observed　by　the　naked　eye　without　the　need　for　the　labeling　or　expensive　equipment.　Given　the　high-performance　for　K-Ras　analysis,　the　enhanced　signal　transduction　capability　associated　with　double-hairpin　structure　of　DHMB　provides　a　novel　rout　to　screen　biomarkers,　and　the　descripted　colorimetric　biosensor　seems　to　hold　great　promise　for　diagnostic　applications　of　genetic　diseases.　(C)　2016　Elsevier　B.V.　All　rights　reserved.