Programmable Target-Initiated DNAzyme Walker Walking along a Spatially Isolated and Highly Hybridizable Substrate Track on a Nanoparticle Surface.

Synthetic DNA machines that operate on the nanoscale three-dimensional (3D) track have attracted rapidly increasing interest because of their potential in biocomputing, drug delivery, and biosensing applications. Current nanoscale 3D DNA tracks are typically created by self-assembling thiolated oligonucleotides at gold nanoparticle (AuNP) surfaces via the strong Au-S chemistry. However, it remains challenging to accurately control the conformation and orientation of the 3D DNA track on AuNP surfaces and finely adjust the hybridization ability of the 3D track. Herein, we describe for the first time a polyadenine (polyA)-based, spatially isolated 3D DNA track, on which a target-initiated DNAzyme walker moves by a burnt-bridge mechanism with improved efficiency and processivity. PolyA serves as an anchoring block for preferential binding with the AuNP surface, and the appended substrate block adopts an upright conformation that favors the hybridization and subsequent DNAzyme-mediated cleavage. The operation of this target-initiated DNAzyme walker was monitored in real time and at a single-particle level. We tested the cleavage efficiency of 3D substrates with various polyA block lengths, which displayed that the DNAzyme activity was remarkably improved as compared with a thiol-based 3D track. We also explored bioanalytical applications of this DNAzyme nanomachine by movement-triggered cascade signal amplification.