Biodegradable MnO₂ nanosheet based DNAzyme-recycling amplification towards: Sensitive detection of intracellular...

A new class of intracellular signal amplification approach, integrating biodegradable manganese dioxide (MnO₂) nanosheet with target-triggered DNAzyme recycling amplification in one nanosystem, was developed for highly specific and sensitive monitoring of microRNAs (miRNAs) in living cells. Briefly, the MnO₂ nanosheets were employed as carrier and quencher for the hairpin-locked-DNAzyme strands (H1). Upon entering cells, the surface-adsorbed strands (H1) can be released due to the degradation of the MnO₂ nanosheets by cellular glutathione. Subsequently, the hybridization reaction between target miRNAs and H1 probe induced the conformation alteration of the hairpin probes H1, formed an "active" DNAzyme. With the assistor of Mg²⁺, the DNAzyme was activated and induced the release of the fluorophores labeled DNA fragment, which achieved the restoration of fluorescence signal. Meanwhile, the target molecules was released and hybridized with the other H1 strand to initiate another cycle of activation, cleavage, and turnovers, which producing enhanced fluorescence signal for sensitive analysis of intracellular miRNAs. Furthermore, fluorescence imaging experiments demonstrated that the MnO₂-DNAzyme nanosystem could visually detect microRNA-21 in cancer cells. The proposed strategy provides a good platform for highly sensitive detection and imaging analysis of various intracellular miRNAs in situ.