We report a silicon-nitride slot-waveguide microring resonator functionalized with monoclonal antibodies against the respiratory syncytial virus (RSV) fusion (F) protein for label-free, real-time detection of RSV. The 100 μm-radius slotted ring exhibits a loaded quality factor of 3.5 × 10⁴ and a bulk sensitivity of 275 nm/RIU at 1310 nm. When challenged with nasopharyngeal swab extracts from RSV-positive patients, the sensor produces wavelength shifts that correlate quantitatively with viral load over a >10³-fold concentration range and show 100% concordance with RT-qPCR on three clinical specimens.
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