Biomolecular　immobilization　and　construction　of　the　sensing　platform　are　usually　crucial　for　the　successful　development　of　a　high-efficiency　detection　system.　Herein　we　report　on　a　novel　and　label-free　signal-amplified　aptasensing　for　sensitive　electrochemical　detection　of　small　molecules　(adenosine　triphosphate,　ATP,　used　in　this　case)　by　coupling　with　target-induced　hybridization　chain　reaction　(HCR)　and　the　assembly　of　electroactive　silver　nanotags.　The　system　mainly　consisted　of　two　alternating　hairpin　probes,　a　partial-pairing　trigger-aptamer　duplex　DNA　and　a　capture　probe　immobilized　on　the　electrode.　Upon　target　ATP　introduction,　the　analyte　attacked　the　aptamer　and　released　the　trigger　DNA,　which　was　captured　by　capture　DNA　immobilized　on　the　electrode　to　form　a　newly　partial-pairing　double-stranded　DNA.　Thereafter,　the　exposed　domain　at　trigger　DNA　could　be　utilized　as　the　initator　strand　to　open　the　hairpin　probes　in　sequence,　and　propagated　a　chain　reaction　of　hybridization　events　between　two　alternating　hairpins　to　form　a　long　nicked　double-helix.　The　electrochemical　signal　derived　from　the　assembled　silver　nanotags　on　the　nicked　double-helix.　Under　optimal　conditions,　the　electrochemical　aptasensor　could　exhibit　a　high　sensitivity　and　a　low　detection　limit,　and　allowed　the　detection　of　ATP　at　a　concentration　as　low　as　0.03　pM.　Our　design　showed　a　high　selectivity　for　target　ATP　against　its　analogs　because　of　the　high-specificity　ATP-aptamer　reaction,　and　its　applicable　for　monitoring　ATP　in　the　spiking　serum　samples.　Improtantly,　the　distinct　advantages　of　the　developed　aptasensor　make　it　hold　a　great　potential　for　the　development　of　simple　and　robust　sensing　strategies　for　the　detection　of　other　small　molecules　by　controlling　the　apatmer　sequence.　©　2015　Elsevier　B.V.　All　rights　reserved.