G-quadruplex-bridged triple-helix aptamer probe strategy: A label-free chemiluminescence biosensor for ochratoxin A

After successively introducing elements of a triple-helix aptamer probe (TAP) and a luminol–hydrogen peroxide (H 2 O 2 ) solution, we proposed a brand-new chemiluminescence (CL)-based biosensor for the assay of ochratoxin A (OTA). Primarily, the TAP contains an aptamer loop, two DNA segment stems, and a triplex-forming oligonucleotide (signal probe). In the presence of a target, the aptamer sequence binds to the target with an impressive affinity. This association leads to a conformational change in the TAP, thus releasing the signal probe. Sequentially, with the participation of hemin and potassium ions, the dissociated probe forms into a G-quadruplex structure that is capable of catalyzing luminol to produce CL mediated by H 2 O 2 . In contrast, in the absence of the target, a low background signal remains. Using this approach of combining a novel TAP switch with a G-quadruplex-catalyzed luminol-H 2 O 2 system, we presented a label-free and signal-on CL strategy for the measurement of OTA. Under optimal conditions, the gradually strengthened signal maintained a linear dependence on target concentrations ranging from 0.1 ng/mL to 2.0 ng/mL, and the detection limit was as low as 0.07 ng/mL. This newly designed, simple, and cost-effective protocol affords high sensitivity, specificity, suitability, and efficacy for biosensing. Thus, this protocol is attractive for a range of target quantifications, with only the matched aptamer requiring replacement (no redesign of signal probes).