Biodegradable nanoparticle-assisted and multiplexed imaging of asymmetric RNA expressions in live cells for precise cancer diagnosis and prognosis

The simultaneous imaging of the dynamic expression variations of regulatory RNAs in cells, which remains a major challenge, has important applications in precise disease diagnosis, treatment and prognosis. Here, we describe the establishment of a biodegradable ZnO nanoparticle (NP)-assisted asymmetric amplification approach for the simultaneous imaging of microRNA-21 (miRNA-21) and programmed cell death 4 (PDCD4) mRNA at distinct expression levels in live cells. The DNA signal probe complexes are immobilized on the ZnO NPs and readily delivered into the target cancer cells via the endocytosis pathway. The acidic microenvironment in cancer cells leads to the dissolution of the ZnO NPs to release Zn²⁺ ions and the intracellular miRNA-21 activates the Zn²⁺-dependent DNAzyme to cleave the substrate signal probes with the assistance of the Zn²⁺ cofactor to show green fluorescence for imaging miRNA-21. Meanwhile, the PDCD4 mRNA can displace the other quenched signal probes to generate red fluorescence. Importantly, the PDCD4 mRNA sequences can be recycled and reused by using the DNAzyme-cleaved sequences as the fuel strands through two strand displacement reactions to yield amplified red fluorescence for detecting low levels of PDCD4 mRNA. Moreover, our approach can be used to evaluate the varied expression levels of miRNA-21 and PDCD4 mRNA responsive to different drugs in cells, reflecting its usefulness for precise cancer diagnosis and prognosis upon anticancer drug treatment.