Recently, Professor Zhao Yongxi's research team at the School of Life Science and Technology of XJTU designed and fabricated a MnO2 nanosheet/DNAzyme (nanozyme) system for improving the assembly efficiency and catalytic activity of DNAzyme so as to realize the intracellular signal amplification of DNA circuit. The MnO2 nanozyme was formed by adsorbing DNA probes with mono-layered MnO2 nanosheets, which can enter a cell easily. Intracellular reductants such as glutathione (GSH) can reduce MnO2 nanosheets to Mn2+, while Mn2+ as DNAzyme cofactor can promote sequence assembly and conformational folding, and significantly enhance the catalytic activity. DNA repair proteins recognized and excised the corresponding damaged DNA modules, then the assembly and the catalytic reactions were initiated, forming a DNA circuit. The circuit can amplify the fluorescence signal and significantly improve the detection sensitivity of low-abundance repair proteins in tumor cells. Designing and utilizing DNA probes that are capable of recognizing different damage types and creating multifunctional MnO2 nanozymes can be used to monitor other repair proteins and pathways. Compared with MnO2 nanozyme, the conventional DNAzyme has low intracellular assembly efficiency and insufficient catalytic activity, which is unable to exhibit strong fluorescence signal.