SERS detection of osteoarthritis-linked microRNA-204 via a DNAzyme-catalyzed self-amplifying circuit.

Sensitive detection of microRNA-204 (miR-204) is critical for the early diagnosis and management of osteoarthritis (OA). This work presents a novel surface-enhanced Raman scattering (SERS) biosensor for the ultrasensitive and specific detection of OA-associated miR-204. The platform integrates a self-amplifying nucleic acid circuit with DNAzyme-catalyzed etching of a plasmonic nanoprobe. At its core is a single, rationally designed overhang-containing hairpin probe (O-HP) that functions as both the recognition element and amplification initiator. Upon binding to miR-204, the O-HP triggers polymerase-mediated extension, generating G-quadruplex structures. These structures bind hemin to form DNAzymes that catalyze the localized production of reactive oxygen species (ROS), which subsequently etch the silver shell of the gold nanostars core with silver shell and 4-aminothiophenol (AuNS/Ag@4-ATP) SERS nanoprobe. This etching causes the desorption of Raman reporters and a quantifiable 'signal-off' response. This biosensor achieves a remarkably low detection limit of 8.13 fM with a broad dynamic range from 10 fM to 150 nM, and exhibits high specificity, capable of discriminating single-nucleotide variants. Furthermore, it successfully quantified miR-204 in clinical cartilage samples, showing a strong correlation with real-time quantitative polymerase chain reaction results. The modular design of the O-HP also facilitated the adaptation of the platform for detecting miR-21, demonstrating its generalizability. This work provides a robust and versatile biosensing strategy with significant potential for clinical miRNA diagnostics.