Dynamically monitoring microRNA (miRNA)-DNA reactions is critical for elucidating various biological processes. However, traditional strategies fail to capture this dynamic event because the original targets are pre-amplified. In the present study, we developed an amplification-free strategy for real-time monitoring of miRNA-DNA hybridization that integrates the advantages of both duplex-specific nuclease (DSN)-triggered signal amplification and single-stranded DNA probe coating facilitated by reduced graphene oxide. DSN-mediated miRNA recognition was found to consist of two phases: hybridization and hybridization-cleavage. In the presence of miRNA and DSN, hybridization of a 22-mer miRNA-DNA could be completed within 7 min by observing the angle increase in a surface plasmon resonance (SPR) biosensor. The subsequent hybridization-cleavage process could be visualized as a gradual SPR angle decrease that occurred until all coated probes were hydrolyzed. In addition, for miRNA-21 detection, the proposed linear signal amplification assay demonstrated a sensitivity of 3 fM over a dynamic range of 5 orders of magnitude.