High-Performance Optical Fiber SPR Biosensor for Label-Free Detection of miRNA-588 Toward Osteosarcoma Diagnosis

Osteosarcoma is a malignant bone tumor for which diagnosis is critical to patient prognosis. MicroRNA-588 is downregulated in osteosarcoma, highlighting its potential as a diagnostic biomarker. However, its low abundance in body fluids makes sensitive detection difficult. This study presents a label-free reflective optical fiber surface plasmon resonance (SPR) biosensor with optimized probe immobilization for ultrasensitive miRNA-588 detection in serum. The sensor utilizes plasmonic coupling between a gold film and gold nanoparticles to enhance the SPR response. By incorporating an A₁₅ anchor and a T₅ spacer into a single oligonucleotide, the A₁₅T₅ probe promotes a more upright presentation of the recognition sequence while simplifying interface construction. Among the configurations evaluated, the A₁₅T₅ probe showed the best performance for miRNA-588 detection. The biosensor exhibits a wide detection range from 10^-15 to 10^-7 M, with a low detection limit (LOD) of 1.12 × 10^-17 M, along with good stability and repeatability. In clinical sample testing, the sensor achieved an area under the receiver operating characteristic (ROC) curve of 0.95 and showed greater diagnostic discrimination than serum alkaline phosphatase in the evaluated cohort. This platform enables high-sensitivity detection of trace biomarkers, supporting the diagnosis of major diseases.