A fluorescence strategy for the rapid detection of miRNA-21 based on G-quadruplex and cyclic amplification signal.

MicroRNAs (miRNAs) are commonly used as biomarkers for the diagnosis of tumors. Since miRNA expression is strongly correlated to carcinogenesis, the detection of miRNA concentration in cells would be valuable for the diagnosis and evaluation of tumors. In this study, we proposed a system using two strands of DNA, one modified by a phosphate group at the 5' end, called Cap, and the other with a hairpin structure, called HP. The Cap chain could open the hairpin structure of HP and expose the sequences rich in G bases to form the G-quadruplex structure. Then, a strong fluorescence signal was emitted in the presence of N-methyl mesoporphyrin IX (NMM). However, with the addition of miRNA-21, Cap hybridized with it to form double chains, which were then cleaved by the digestion of lambda exonuclease, resulting in a weak fluorescent signal. The proposed method could detect miRNA-21 at a concentration of 1.4 pM with a broad dynamic linear range from 5 pM to 5 nM.