Catalytic hairpin assembly indirectly covalent on Fe₃O₄@C nanoparticles with signal amplification for intracellular detection of miRNA

Fluorescence resonance energy transfer, a promising method for in situ imaging of miRNA in living cells, has intrinsic limitation on sensitivity and selectivity. Herein, a fluorescent amplification strategy based on catalyzed hairpin assembly indirectly covalent on Fe₃O₄@C nanoparticles via short single-stranded DNA was investigated for cellular miRNA detection in living cells, integrating non-enzyme target-active releasing for amplifying the signal output, highly quenching efficiency of Fe₃O₄@C nanoparticles with low background, ssDNA assisted fluorescent group-fueled chain releasing from Fe₃O₄@C nanoparticles with enhanced fluorescence response. The designed platform exhibits highly sensitive in a wide linear concentration range of 0.450 pM–190 pM and is highly specific for miRNA-20a detection with the ability of discriminating one mistake base. Additionally, the CHA-Fe₃O₄@C was successfully applied in imaging visualization of miRNA-20a in the living cell. The strategy provides a promising bioassay approach for clinical research.