Highly integrated, self-powered and activatable bipedal DNA nanowalker for imaging of base excision repair in living cells

DNA walkers have attracted considerable attention in biosensing and bioimaging. Compared with the conventional single leg-based DNA walker, the bipedal DNA walker has remarkable advantages, with improved sensitivity and fast kinetics, and can work efficiently in a crowded cellular environment. However, most reported bipedal DNA walkers are powered by exogenous supplementation, and elaborate DNA sequence designs, auxiliary additives or extra carriers are often needed. A highly integrated bipedal DNA walker that can address robustness, sensitivity and consistency issues in a single system is highly desirable but remains a great challenge. We herein report a novel bipedal DNA nanowalker system through simple assembly of a DNA substrate, hairpin functionalized-AuNPs (AuNPs-H2), and a blocked Mn²⁺-dependent DNAzyme hairpin (H1) on degradable MnO₂ nanosheets, which holds great potential for living cell operation. Highly integrated features enable the simultaneous delivery of core components of the bipedal DNA walker, including a walking track (AuNPs-H2), a walking strand (H1 cleaved by APE1), and a driving force (Mn²⁺-dependent DNAzyme cleavage) as a whole, thereby enhancing the control of the spatiotemporal distribution of these components at the intracellular target sites. The redox reaction between the MnO₂ nanosheets and GSH inside the cells not only consumed the intracellular GSH to improve the biostability of the walking track but also generated abundant Mn²⁺ as a cofactor of the DNAzyme. As a proof of concept, the developed nanowalker was demonstrated to work efficiently for monitoring base excision repair (BER)-related human apurinic/apyrimidinic endonuclease 1 (APE1) in living cells, highlighting the great potential of the bipedal DNA nanowalker in biological systems.