Self-assembled DNA/RNA nanospheres with cascade signal amplification for intracellular MicroRNA imaging

In situ visual detection of microRNAs (miRNAs) is of great significance for early diagnosis of miRNA-related diseases. In this study, we designed a rolling circle replication-driven self-assembled nucleic acid nanosphere (NS) for imaging miRNAs in living cells, which was loaded with four functional oligonucleotides (THp, H1, H2, H3) through hybridization. The DNA/RNA NS showed excellent biocompatibility, stability and RNase H-responsiveness, enabling on-demand delivery of sensing components and live-cell applications. In the presence of the target miRNA, the cascade amplification of catalytic hairpin assembly (CHA) and hybridization chain reaction (HCR) would be triggered to generate a strong fluorescence signal. Taking miRNA 155 as a model, the developed DNA/RNA NS achieved sensitive detection of the target in vitro and in tumor cells, demonstrating the potential of miRNA-based tumor screening.