Design of aptamer-based sensing platform using triple-helix molecular switch.

For successful assay development of an aptamer-based biosensor, various design principles and strategies, including a highly selective molecular recognition element and a novel signal transduction mechanism, have to be engineered together. Herein, we report a new type of aptamer-based sensing platform which is based on a triple-helix molecular switch (THMS). The THMS consists of a central, target specific aptamer sequence flanked by two arm segments and a dual-labeled oligonucleotide serving as a signal transduction probe (STP). The STP is doubly labeled with pyrene at the 5'- and 3'-end, respectively, and initially designed as a hairpin-shaped structure, thus, bringing the two pyrenes into spacer proximity. Bindings of two arm segments of the aptamer with the loop sequence of STP enforce the STP to form an "open" configuration. Formation of aptamer/target complex releases the STP, leading to new signal readout. To demonstrate the feasibility and universality of our design, three aptamers which bind to human a-thrombin (Tmb), adenosine triphosphate (ATP), and L-argininamide (L-Arm), respectively, were selected as models. The universality of the approach is achieved by virtue of altering the aptamer sequence without change of the triple-helix structure.