We have carefully designed a probe for in situ detection and imaging of Argonaute2 (Ago2), a key RNA interference (RNAi) protein in human cells and siRNA (Let-7a) interactions. The probe mainly contains two parts: a gold nanoparticle (AuNP) being quenched and a functionalized nucleic acid as a fluorescent output carrier. After the probe is endocytosed into the cell, the modified hairpin nucleic acid can be cut into two parts by the Ago2/Let-7a complex (ALC). The cut nucleic acid will replace a DNA strand modified on another duplex nucleic acid. The replaced DNA strand’s 3’-end is modified with a fluorophore (Cy3). By cascading single cells, the probe can directly achieve the fluorescence recovery of the probe in the cell. By dynamically monitoring the in-situ quantitative response of the interaction between Ago2 and Let-7a, and distinguishing between strongly RNA-expressing cells and other cells, the interaction between Ago2 and Let-7a can be monitored dynamically, proving the utility of the probe. Probes will accelerate the basic role of reducing protein-RNA interactions, the mystery of RNA silencing, and monitoring the treatment of cancer.