Autocatalytic DNA nanosphere assembly activated by endogenous APE1 for intracellular miR-21 imaging.

MicroRNAs (miRNAs) are promising cancer biomarkers, yet their intracellular detection remains constrained by limited amplification efficiency, nonspecific activation, and nuclease-mediated probe degradation. Here, we developed an APE1-activated nanosphere assembly (ANA) system for the specific and sensitive imaging of miR-21. The ANA system employs tumor-specific APE1 activation to initiate autocatalytic catalytic hairpin assembly among DNA nanospheres, generating crosslinked nanostructures and amplified fluorescence signals. Furthermore, the compact nanosphere architecture confers nuclease resistance, ensuring reliable probe performance under complex biological conditions. The proposed system exhibited a detection limit of 1.93 pM with high specificity for miR-21. For biological applications, the ANA system effectively distinguished cancerous from healthy cells, and this discrimination capability was further extended to clinical breast tissue samples. Overall, this work provides a robust platform for specific and sensitive intracellular miRNA imaging with potential applications in early cancer diagnosis.