Catalytic hairpin self-assembly regulated chameleon silver nanoclusters for the ratiometric detection of CircRNA.

CircRNA, a group of circular, closed, single-stranded non-coding RNA, is an important biomarker for cancer diagnosis and prognosis. Sensitive and selective detection of circRNA can greatly facilitate the early diagnosis of human diseases. Herein, an isothermal amplification system is proposed based on dual-catalyzed hairpin self-assembly (CHA) and chameleon DNA templated silver nanoclusters (DNA-AgNCs) for the label-free ratiometric detection of circRNA. The upstream CHA1 could be specifically triggered by the analyte to form double-stranded DNA (dsDNA) products, leading to the red fluorescence of hairpin DNA-AgNCs decreased due to the destruction of the hairpin structure. The resulting dsDNA, with a trigger sequence, could then further activate downstream CHA2 to generate another dsDNA complex, which induced the other dark AgNCs to approach the G-rich sequence, thereby causing a dramatic increase in green fluorescence. Thus, by measuring the distinct variation in the ratios of green and red fluorescence intensities, the ratiometric system could be used to sensitively detect and visually distinguish the circRNA. In addition, the two-stage signal amplification in the CHA cycle endowed the detection method with ultra-sensitive detection performance, in which the detection limits for the RNA target were honed to 1 pM. Moreover, this novel method can be used as a general strategy to analyze different types of circRNA, thus showing its great potential for the detection of low abundant biomarkers in various clinical research studies.