Dumbbell Hybridization Chain Reaction Based Electrochemical Biosensor for Ultrasensitive Detection of Exosomal miRNA.

Exosomal miRNA is an ideal source of noninvasive biomarker for the diagnosis of cancer. Sensitive and accurate analysis of exosomal miRNA plays an important role in facilitating clinical applications. Herein, we have developed a novel electrochemical method for exosomal miRNA assay coupling strand displacement amplification (SDA) and dumbbell hybridization chain reaction (DHCR). The target triggered isothermal SDA process generates a large number of single-stranded DNA products to assist the formation of the three-way junction structure on the electrode surface. In addition, dumbbell DNA fuel strands (DHP1 and DHP2) are designed for the hybridization chain reaction. This novel form of HCR produces DNA nanostructures with a tight conformation, which facilitates the enhancement of the electrochemical response. The combination of the dual signal amplification significantly improves the sensitivity for the exosomal miRNA assay, resulting in a limit of detection (LOD) as low as 7.3 aM. More importantly, the method is successfully applied in the analysis of cells and human serum samples, which demonstrates the potential utility in point-of-care testing (POCT) applications.