2-aminopurine probe in combination with catalyzed hairpin assembly signal amplification for simple and sensitive detection of microRNA

A quencher-free and enzyme-free fluorescent sensor was proposed to simply and sensitively detect miRNA via the target catalyzed hairpin assembly (CHA) signal amplification in combination with 2-aminopurine (2-AP) molecular beacon (MBs). This sensor contains two DNA hairpins termed as Hi and H2. H1 labeled by 2-AP needs no quenchers because 2-AP can be quenched through its stacking interaction with the adjacent bases. H2 is partially complementary to H1. In the presence of the target microRNA (miRNA), H1 is unfolded and produces the DNA/RNA complexes, enhancing the fluorescent signal. Then, the RNA of the DNA/RNA complexes can be displaced by H2 and the free miRNA can interact with another H1, resulting in the significant fluorescence enhancement of the system. This signal amplification process is enzyme-free, making the sensor more simple and cost effective. The detection limit of this sensor could be as low as 3.5 pM. We further applied this assay to monitor the overexpressed miRNA-21 from human breast cancer cells to confirm its applicability. The proposed sensor could be used as a simple and sensitive platform for target miRNA detection, holding great potential for convenient monitoring of different miRNA biomarkers for early diagnosis of various cancers.