Multiplex microRNA imaging in living cells using DNA-capped-Au assembled hydrogels

Non-invasively imaging multiplex microRNAs (miRNAs) in living cells is pivotal to understanding their physiological functions and pathological development due to the key regulatory roles of miRNAs in gene expression. However, developing smart delivery systems with large gene loading capacity, biocompatibility and responsiveness remains a significant challenge. Herein, we successfully incorporated DNA-capped Au nanoparticles (NPs) and their complementary fluorescent DNA sequences into a porous 3D hydrogel network (AuDH), in which hairpin-locked DNAzyme strands and active metal ions were loaded (AuDH/M(n+)/H) for simultaneously imaging multiplex miRNAs in living cells. After transfection into cells, the specific miRNAs trigger the strand-displacement reaction and sequentially activate the DNAzyme-assisted target recycling, leading to a strong increase in the corresponding fluorescence intensity for imaging. This enables simultaneous assessment of the abundance of multiplex cancer-related miRNAs, even if at a very low expression level, in different cells through the different fluorescence intensities due to the dual signal amplification, and the change in abundance of miRNAs induced by siRNA or miRNA mimics in living cells can also be efficiently monitored. The versatile and responsive DNA hydrogel system holds great potential for miRNA biomedical applications.