Intracellular CircRNA imaging and signal amplification strategy based on the graphene oxide-DNA system.

CircRNA is a type of covalently closed circular RNA molecule that serves as a potential biomarker for the disease early diagnosis and clinical researches. To achieve living cell imaging of specific circRNA, we developed a novel graphene oxide (GO)-based catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) signal dual amplification system (GO-CHA-HCR, abbreviated GO-AR) for circ-Foxo3 imaging in living cells. The developed system consists of four types of designed hairpin DNA HP1, HP2, H1, and fluorophore-labeled H2, which are absorbed on the GO nanosheets surface leading to fluorescence quenching. In the presence of circ-Foxo3, the CHA cycle was initiated to form a hybrid chain with split fragments, which triggered the HCR cycle to generate dsDNA nanowires that were then released from GO. This process recovered the quenched fluorescence, realizing two-stage signal amplification. The GO-AR system effectively improved the signal-to-noise ratio compared to the traditional GO-CHA and GO-HCR detection system. The detection limit of circ-Foxo3 was as low as 15 pM with excellent sensitivity and selectivity. In addition, the enzyme-free sensing system was successfully applied in living cell circRNA imaging and serum circRNA detection, indicating its high potential in clinical diagnostics.