This　work　reports　the　proof-of-concept　of　an　ultrasensitive　label-free　electrochemical　aptasensor　for　Kanamycin　(Kana)　detection　coupling　strand-displacement　amplification　(SDA)　with　hybridization　chain　reaction　(HCR).　In　the　presence　of　target　Kana,　the　analyte　triggers　conformational　change　of　hairpin　HP1　(HP1)　and　two-staged　SDA　to　produce　short　single-stranded　DNA　(S1)　with　the　aid　of　KF　polymerase　and　nicking　endonuclease.　Meanwhile,　the　as-produced　S1　hybridizes　with　the　immobilized　hairpin　HP2　(HP2)　on　the　electrode　to　open　the　hairpin,　thereby　resulting　in　the　formation　of　DNA　duplex.　Thereafter,　DNA　duplex　is　selectively　digested　by　Exo　III　accompanying　S1　recycling.　The　residual　single-stranded　probe　(S2)　on　the　electrode　opens　another　two　hairpins　in　sequence　and　propagates　a　chain　reaction　of　hybridization　events　between　two　alternating　hairpins　(H1　and　H2)　to　form　a　long　nicked　double-helix.　Upon　addition　of　redox-active　methylene　blue　(MB),　numerous　indicators　are　intercalated　into　the　grooves　of　double-helix　DNA　polymers,　each　of　which　produces　an　electrochemical　signal　within　the　applied　potentials.　Under　optimum　conditions,　the　SDA/HCR-based　electrochemical　aptasensor　exhibits　a　high　sensitivity　for　detection　of　Kana　down　to　36　fM　with　a　linear　range　from　0.05　to　200　pM.　Additionally,　the　as-prepared　aptasensor　is　successfully　employed　to　determinate　the　Kana　in　animal　derived　food　(milk).　With　the　advantages　of　high　sensitivity,　label-free　strategy　and　excellent　selectivity,　the　developed　aptasensor　possesses　great　potential　application　value　in　food-safety　analysis　field.　(C)　2018　Elsevier　B.V.　All　rights　reserved.