Smart Catalyzed Hairpin Assembly-Induced DNAzyme Nanosystem for Intracellular UDG Imaging

Uracil DNA glycosylase (UDG) is one of the key initiators for the base excision repair pathway. Since abnormal UDG expression is associated with various diseases, sensitive detection of UDG activity is critical for early clinical diagnosis. Here, a smart catalyzed hairpin assembly (CHA)-DNAzyme nanosystem is developed for intracellular UDG imaging by incorporating CHA and DNAzyme onto MnO2 nanosheets. In this strategy, the biodegradable MnO2 nanosheets are employed as nanocarriers for efficiently adsorbing and delivering five DNA probes into cells by endocytosis. Then, the MnO2 nanosheets are degraded by cellular glutathione to release the DNA modules at the same intracellular position. Liberated Mn2+, an indispensable DNAzyme cofactor, was used to promote catalytic cleavage for facilitating the cascade process in cells. Based on the uracil site-recognition and -excision operation of the target UDG, the activated CHA-DNAzyme nanosystem generates lots of DNAzyme-assisted CHA products, turning on the fluorescence resonance energy transfer response. This autocatalytic CHA-DNAzyme nanosystem provides a detectable minimum UDG concentration of 0.23 mU/mL, which is comparable to some reported UDG detection approaches. As a multiple signal amplification strategy, the CHA-DNAzyme nanosystem realizes the UDG imaging in living cells with enhanced sensitivity, indicating great promise in the prediction and diagnosis of early-stage cancer.