To illustrate the feasibility of employing a nanopore as a single-molecule stochastic sensing element for C9-HRE detection, the translocation of ASO-Tr, H1, H2, and H1-H2 hybridization complexes in the nanopore was first investigated at an applied potential bias of +120 mV. In line with our expectations, each of the three structures gave rise to unique translocation events that were easily distinguishable from one another (
Fig. 2). In this report, the open pore current was defined as
Io, the residual current was
I, and the event dwell time was
t. The percentage blockade was defined as (
Io -
I)/
Io. The event histogram data was analyzed using a Gaussian distribution. In the present study, the characteristic ionic current blockades elicited by both ASO-Tr and hairpin (H1 and H2) were observed, which incorporated two residual current levels: a shallow blockade (level 1) and a deeper one (level 2) (
Figs. 2A–
C). The percentage blockade for ASO-Tr, H1 and H2 at current level 1 were 0.43 ± 0.01, 0.33 ± 0.01 and 0.35 ± 0.01, respectively. For current level 2, ASO-Tr, H1 and H2 showed 0.82 ± 0.01, 0.78 ± 0.01 and 0.79 ± 0.04, respectively. The dwell times at level 1 for ASO-Tr, H1, and H2 were 2.82 ± 0.05 ms, 3.52 ± 0.10 ms and 2.87 ± 0.08 ms, respectively. Meanwhile, the dwell times at level 2 were 0.54 ± 0.03 ms, 0.55 ± 0.07 ms, and 0.18 ± 0.02 ms for ASO-Tr, H1, and H2, respectively. As mentioned in our previous work, the shallow blockage of the hairpin was caused by its collision with the vestibule of the MspA nanopore, whereas the deeper blockage was brought about by efficient translocation [
36]. The voltage-dependent experiment also supported the conclusions (Figs. S2–S4 in Supporting information). Notably, the type of events and properties of ASO-Tr were consistent with the hairpin structure. Most likely, ASO-Tr contained a loop structure that could collide with the MspA nanopore vestibule, just as the previously reported hairpin structure interacted with MspA [
36]. Similar to other dsDNA translocate through the nanopore, only one type event was observed for H1-H2 hybridization complexes translocating through the MspA nanopore, with the blockade rate at 0.84 ± 0.002 and the dwell time at 3.32 ± 0.05 ms (
Fig. 2D and Fig. S5 in Supporting information). Given that the translocation events are voltage- and concentration-dependent [
37], the current events of H1-H2 hybridization complexes were further characterized by voltage- and concentration-dependence in this investigation. The results demonstrated that the dwell time exhibited strong voltage-dependent (
Fig. 2F). Simultaneously, the translocation events frequency increased linearly with increasing H1-H2 hybridization complexes concentration (
Fig. 2E). The above results confirmed that target-triggered CHA amplification strategy could be used to detect C9-HRE.