Target-Mediated EV-SNA Clustering as an Amplifier for In Situ miRNA Imaging in Living Cells

To overcome the low efficiency of probe delivery and the comprised detection limit due to dispersion of fluorescent molecules, we develop a miRNA detection–amplification system, called the miRDAS, which can be rapidly internalized by cells and amplify miRNA signals in situ within living cells. The miRDAS consists of two types of extracellular vesicle spherical nucleic acid (EV-SNA), named EVsnater and EVsnafier, which are generated by hydrophobic coassembly of natural EVs with cholesterol-modified oligonucleotides and exhibit rapid cellular uptake dynamics. Upon specifically binding to its target miRNA, the EVsnater activates the fluorescence and then self-assembles with EVsnafier to form giant fluorescent clusters, resulting in a brighter and significantly amplified fluorescence signal. Additionally, the miRDAS exhibits excellent flexibility and orthogonality, thus enabling simultaneous detection of multiple miRNA targets. As a proof of concept, a miR-124 miRDAS was designed and employed for successfully monitoring miR-124 expression levels during P19 neuronal differentiation.