Target-Triggered Cascaded Self-Feedback DNAzyme Circuit Loaded in ZIF-8 for Highly Sensitive miRNA Imaging in Living Cells

The highly sensitive and rapid imaging of miRNA in living cells promises to advance our understanding of diseases and promote their diagnosis and treatment. To enhance the sensitivity of miRNA imaging, a series of cascade signal amplification strategies based on enzyme-free methods have been developed. However, these cascaded amplification strategies involve complex designs and multiple amplification mechanisms, leading to potential side effects. Herein, we have developed a novel hairpins@ZIF-8 nanosystem by rationally integrating ZIF-8 with a cascaded self-feedback DNAzyme circuit (CSDC), achieving highly sensitive and rapid imaging of miRNA in living cells. ZIF-8 facilitates the efficient transfection of nucleic acid probes into cells and provides the necessary cofactor ions for CSDC. The developed CSDC possesses exponential amplification based solely on the DNAzyme mechanism. Benefiting from the exponential amplification efficiency, the CSDC exhibited higher sensitivity than traditional DNAzyme-based amplification, with a detection limit of 2.28 fM, approximately 10⁵ times more sensitive than traditional DNAzyme-based amplification. This hairpins@ZIF-8 nanosystem demonstrated strong practical application capabilities, effectively reflecting fluctuations in intracellular miRNA levels and successfully distinguishing between normal and tumor cells based on miRNA expression differences. It could also be applied for in vivo miRNA imaging. This proposed strategy is anticipated to pave the way for innovative amplification approaches and serve as a vital instrument in miRNA-related research, diagnosis, and treatment.