Abstract
DNA molecular machines show great promise in fields such as biomarker discovery and biological activity regulation, but operating DNA machines with specific functions within living systems remains extremely challenging. Although DNA machines have been engineered with exact molecular-level specifications, some intrinsic imperfections such as poor cell permeation and fragility in complex cytoplasmic milieu persist due to the well-established character of nucleic acid molecules. To circumvent these problems, we herein report a molecularly engineered, entropy-driven three-dimensional DNA amplifier (EDTD) that can operate inside living cells in response to a specific mRNA target. In particular, mRNA target/EDTD interaction can specifically initiate an autonomous DNA circuit inside living cells owing to the exclusive entropy-driven force, thus providing enormous signal amplification for ultrasensitive detection of the mRNA. Moreover, owing to molecular engineering of a unique DNA tetrahedral framework into the DNA amplifier, EDTD exhibits significantly enhanced biostability and cellular uptake efficiency, which are prerequisites for DNA machines used for in vivo applications. This programmable DNA machine presents a simple and modular amplification mechanism for the detection of intracellular biomarkers. Moreover, this study provides a potentially valuable molecular tool for understanding the chemistry of cellular systems and offers a design blueprint for further expansion of DNA nanotechnology in living systems.