A homogeneous label-free electrochemical aptasensor based on an omega-like DNA nanostructure for progesterone...

A novel homogeneous label-free electrochemical aptamer sensor for the detection of progesterone was prepared by combining a well-designed omega (Ω)-like DNA (Ω-DNA) nanostructure, with an isothermal cycling amplification strategy based on the highly efficient exonuclease III (Exo III). The omega-like (Ω) DNA is composed of two oligonucleotide strands: DNA₁ and DNA₂. The Pro aptamer triggers a chain displacement reaction of Ω-DNA nanostructures, forms a new double-stranded DNA structure (aptamer precursor-DNA₂), and releases DNA₁. Then, Exo III selectively cleaves the DNA duplex and releases the Pro aptamer to participate in a new displacement reaction. Meanwhile, the released DNA₁ strands gain access to the strongly bound hemin, forming a hemin/G-quadruplex (DNAzyme). In the presence of hydrogen peroxide (H₂O₂), differential pulse voltammetry (DPV) was used to detect the current signal from the oxidation of o-phenylenediamine (OPD) to aminoazobenzene (DAP) catalyzed by DNAzyme. However, the amount of released DNA₁ from the Ω-DNA nanostructures is reduced in the presence of the target Pro, and the DPV signal declines because of the small amount of DNAzyme formed. The developed electrochemical aptasensor has a wide dynamic linear relationship in the range of 1 pg mL^-1 to 10 ng mL^-1 under optimal conditions. Its detection limit is down to 0.3 pg mL^-1, providing a potential platform for a sensitive Pro assay among electrochemical assays.