Incorporating elements of triple-helix aptamer probes (TAP), catalyzed hairpin assembly (CHA) signal amplification and host-guest recognition, a novel "signal-on" sensing strategy for sensitive electrochemical quantification of tetracycline (TC) was reported unprecedentedly. TAP was formed involving an aptamer loop, two-segment stems and a triplex oligonucleotide serving as trigger probe. Then, the trigger probe would be released from TAP once the target presented due to the conformational variation of TAP induced by aptamer binding event, sparking off the upcoming CHA amplification reaction, in which two coexisting DNA hairpins (H1 and H2 both modified with the electroactive molecules) would hybridize into plentiful H1-H2 double helices. Afterwards, the Exonuclease III was added, demolishing double helices and simultaneously releasing plentiful electroactive molecules which were capable of diffusing onto the electrode surface under the assistance of β-cyclodextrin due to host-guest recognition, where appreciable signals were enriched and generated. As thus, considerably slight amounts of targets though, emitted trigger probes, yet efficiently engining spectacular CHA cycles of reactions through which amplified signals were yielded, and in turn progressively enabling the sensitive target detection done. Under optimal conditions, the growing signal stayed a linear relation along with the logarithm of the target concentrations ranging from 0.2 nM to 100 nM, the detection limit reaching as low as 0.13 nM. This approach was desirable regarding to sensitivity, detection limit and range, prospectively rendering a service for diverse targets detection by easily replacing the matched aptamer loop of TAP.