Transient toehold: An interesting transient molecular event for controlled DNA displacement reactions and assay of progesterone with aptamer probe

Progesterone is a typical one of endocrine-disrupting chemicals and its environmental residues pose risks to human health. DNA aptamers are powerful bio-receptors and it is desirable to develop new signal translators for aptamer probes to assay progesterone. Here an interesting DNA transient molecular event was firstly found to activate DNA strand displacement, and then an aptamer probe to assay progesterone was developed by combining this “transient toehold” and an exonuclease-mediated strategy. The transient toehold has been successfully characterized in detail, and can continuously tune the kinetics of DNA strand displacement by multi-parameters. Then in the proposed assay, progesterone can protect its aptamer probe from the degradation by dual exonucleases, regulating the following transient toehold-mediated DNA strand displacement. The aptamer probe exhibited a linear range of 1–20 μM for progesterone, and the limit of detection (LOD) was further estimated to be 500 nM. The assay also showed good selectivity for target progesterone over other endocrine-disrupting chemicals with similar structure. Moreover, the aptamer probe demonstrated robust signal response in real samples, and thus has the good applicability to detect progesterone in environmental or clinical analysis. • One novel and interesting DNA transient molecular event was firstly reported. • The“transient toehold” can activate DNA strand displacement in an unique manner. • Aptamer probes were developed for assay of progesterone using “transient toehold”.