"Repaired and initiated" intramolecular DNA circuit enables the amplified imaging of DNA repair enzyme activity in live cells.

Intramolecular catalytic hairpin assembly (intraCHA) has recently been developed. However, non-nucleic acid-initiated intraCHA is rarely explored. The only protein-initiated intraCHA depends on the unwarrantable binding affinity between protein and its aptamer, which generally results in limited initiation efficiency. Herein, a "repaired and initiated" intraCHA (RI-intraCHA) nanosystem was designed and its operation was reported for amplified imaging of DNA repair enzyme activity in live cells. 8-oxoguanine (8-OG) DNA glycosylase was selected as the model DNA repair enzyme. The RI-intraCHA nanosystem was constructed by linking a dsDNA (containing 8-OG sites and trigger strand), two hairpins to different vertexes of DNA tetrahedron. The nanosystem could independently enter into live cells in virtue of cell permeability of DNA tetrahedron. Upon repair action of endogenous 8-OG DNA glycosylase, intraCHA reaction in the nanosystem was initiated efficiently, generating amplified fluorescence signal. The nanosystem provided a detection limit of 0.2443 U/mL for 8-OG DNA glycosylase, which was lower than that of the reported imaging approaches. Furthermore, the nanosystem exhibited satisfactory biosafety and biostability, achieving amplified imaging of intracellular 8-OG DNA glycosylase activity. The designed RI-intraCHA nanosystem provided a promising tool for the research of basic biology of intracellular DNA repair enzymes as well as their clinic correlations. Schematic representation of the "repaired and initiated" intramolecular catalytic hairpin assembly (RI-intraCHA) nanosystem for amplified imaging the activity of intracellular 8-oxoguanine (8-OG) DNA glycosylase (a model DNA repair enzyme). [Display omitted] • "Repaired and initiated" intramolecular catalytic hairpin assembly system was showed. • The system depended on the repair action of 8-oxoguanine DNA glycosylase. • High efficient initiation of intramolecular catalytic hairpin assembly was achieved. • The system entered cells independently with satisfactory biosafety and biostability. • Amplified imaging intracellular 8-oxoguanine DNA glycosylase activity was realized. [ABSTRACT FROM AUTHOR]