Hybrid plasmonic fiber optic sensor enabling rapid and amplification-free nucleic acid determination for disease screening.

A tilted fiber Bragg grating-surface plasmon resonance biosensing platform is reported for rapid, amplification-free determination of viral nucleic acids in complex clinical matrices. The transducer integrates Au nanoparticles, Ta2C-MXene, and an Au film into a hybrid plasmonic architecture that creates a stereoscopic refractive index sensing region through localized gap-plasmon coupling. Finite element modeling reveals that the three-dimensional electromagnetic field extends the effective sensing volume beyond the classical near-field limit. The field also generates strong gradients that induce dielectrophoretic forces. This mechanism actively enriches analytes at the sensing interface, thereby enhancing signal transduction. Experimentally, a co-immobilized hybrid DNA probe strategy was employed to improve the capture efficiency of long and structured viral sequences. The combination of the dual-probe recognition interface and the optimized plasmonic transducer enables direct, amplification-free determination of severe acute respiratory syndrome coronavirus 2 nucleic acids. Using nasopharyngeal swab samples, the platform achieves a limit of detection of 130 copies·µL–1. The average diagnostic time is approximately 61 s. The sensor exhibited agreement with qRT-PCR results across 30 clinical samples and retained high sensitivity in 10-in-1 pooled testing.