Accurate and sensitive fluorescence detection of DNA based on G-quadruplex hairpin DNA.

A facile and cost-effective fluorescence biosensor is constructed for the accurate and sensitive determination of DNA. The G-quadruplex-forming sequence in hairpin DNA sequence (H1) is originally locked. When target DNA is present, the hairpin structure of H1 can be unfolded and part of H1 hybridized with the target DNA to form a double-stranded DNA and a G-quadruplex. The hairpin DNA sequence (H2) hybridizes with the unfolded H1 and displaces the target DNA. Finally, the displaced target DNA again hybridizes with the H1 and initiates cycle amplification. Thus, the numerous G-quadruplexs at the H1 ends are formed, resulting in the fluorescent enhancement after binding with N-methyl mesoporphyrin IX (NMM). Lower background signal improves the accuracy of assay. The enzyme-free method can detect down to 40pM and a linear range of 3 orders of magnitude. Moreover, this strategy has an ability to discriminate the target DNA from even single-base mismatched or other sequence. The proposed method has potential applications in DNA-based molecular diagnostics.