The involvement of microRNA (miRNA) in the transcriptional and regulatory processes of gene expression in organisms, along with its aberrant expression patterns in various malignant diseases such as tumors, underscores its significance. Surface-enhanced Raman scattering (SERS) biosensing technology offers distinct advantages for miRNA detection, including simplified procedures, non-destructive analysis, fingerprint spectroscopy capabilities, and rapid detection times. This study presents the development of a novel SERS-based biosensor utilizing miRNA-21 stimulated-responsive DNA-functionalized nanomaterials. The DNA structure within the the catalyzed hairpin amplification (CHA) was utilized to modify Fe3O4 and Au nanocubes (Au NCs), and subsequently, miRNA21 served as a key to trigger the CHA reaction between these two materials. Notably, during this process, the signal probe Cy3 underwent directed migration and accumulation from Fe3O4 to Au NCs, resulting in the unidirectional enrichment of beacon probe from Fe3O4 to Au NCs, which was facilitated by the progression of the CHA cycle. This facilitated robust generation of SERS signals for precise quantification of miRNA-21. The sensor utilized Au NCs enriched with Cy3 to form highly stable and well-ordered two-dimensional arrays at the water-cyclohexane interface, demonstrating exceptional stability and reproducibility. It achieved an impressive detection limit of 0.81 fM across a dynamic range from 1 to 1 × 10⁶ fM. This work advances practical methods for amplification analysis in the sensing field, demonstrating significant potential for clinical medicine and early cancer diagnosis.