Hand-in-hand structured DNA monolayer for dual-mode analysis of circulating tumor DNA

• Hand-in-hand DNA monolayer is successfully assembled and engineered at the interface of electrode. • Novel DNA nanostructures are constructed for amplified detection of circulating tumor DNA. • An ultrasensitive ratiometic biosensor is developed, which has potential utility in clinical applications. DNA nanostructures with different functions have been extensively studied and applied. Controllable and programmable assembly of functional DNA nanostructures still requires in-depth investigation to guarantee accurate and reliable practical utility. In this study, we have extended the conception of common molecular beacon for the fabrication of novel DNA nanostructures. Three hairpin fuel strands are designed for target circulating tumor DNA triggered construction of three-way junction structures. By the conjugation of swing arms, hand-in-hand DNA monolayer is achieved at the electrode surface. On one hand, electrochemical species could be located near electrode interface due to this structure for electrochemical output; on the other, the hand-in-hand pattern could be cleaved after the addition of DNAzyme cofactor and the released strands carry abundant carbon nanodots for fluorescent out. With the dual-mode analysis, highly selective and reliable detection of target is achieved. The high sensitivity of the proposed method is attributed to the recycling of target strands during the formation of multiple three-way junctions. It holds great potential for the application of DNA analysis and clinical diagnosis.