A DNAzyme dual-feedback autocatalytic exponential amplification biocircuit for microRNA imaging in living cells.

Autocatalytic biocircuit are powerful tools for analysing intracellular biomarkers, but these tools are constrained by limitations in amplification capacity and intracellular delivery efficiency. In this work, we developed a DNAzyme-based dual-feedback autocatalytic exponential amplification biocircuit sustained by a honeycomb MnO2 nanosponge (EDA2@hMNS) for live-cell imaging of intracellular low-abundance microRNAs (miRNA). The EDA2 biocircuit comprises a blocked DNAzyme (b-DNAzyme), a Fuel strand and a Substrate strand. In the EDA2 biocircuit, target miRNAs are recycled and feedback for rounds of DNAzymatic amplification, and the DNAzymatic reactions continuously generate target miRNA analogues for dual-feedback to achieve multiple parallel cascade DNAzymatic reactions that improve amplification capacity substantially. In addition, the hMNS ensures high loading and delivery efficiency of biocircuit probes into living cells and also provides sufficient Mn2+ DNAzyme cofactor from in situ decomposition by intracellular glutathione (GSH). The EDA2@hMNS realized a detection limit of 17 pM, which is 288-fold lower than the b-DNAzyme lacking the DNAzymatic amplification. These results demonstrate the great promise for this critical tool in analysing low-abundance biomarkers and cancer diagnostics.