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 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.