Ultra-sensitive fluorescent sensor for intracellular miRNA based on enzyme-free signal amplification with carbon nitride nanosheet as a carrier

A novel ultra-sensitive fluorescent sensor for monitoring microRNA (miRNA) in living cells was constructed by utilizing a hybridization chain reaction (HCR) as the signal amplification with a carbon nitride nanosheet (CNNS) as a carrier. The Cy5-labeled hairpin DNA could be adsorbed onto the surface of CNNS, resulting in fluorescence quenching of Cy5. When treated with complementary miRNA, the fluorescence was recovered because miRNA could efficiently trigger an HCR, which led to the release of the HCR products from the CNNS. This intracellular HCR strategy can be used for ultra-sensitive monitoring of intracellular miRNA. The main advantages of the proposed method are its simplicity, high sensitivity, high specificity and low toxicity for monitoring low-level biomarkers.