Q-Switching Nanophotonic Biosensing

Sensitive, label-free detection of biomarkers is critical for clinical diagnostics. However, conventional nanophotonic biosensors, typically based on single-oscillator architectures, remain confined to either real or imaginary sensing domain. This isolation often results in weak signal responses, limited operational stability, and high instrumental complexity. We introduce a Q -switching sensing mechanism based on strongly coupled-oscillators that bridges the real and imaginary domains of nanophotonic biosensing. This mechanism amplifies subtle variations in the real part of the refractive index into pronounced switching of the radiative quality factor, enabling robust, intensity-based signal readout. The Q -switching sensing chip is implemented in a defect-tolerant, nonlocal three-dimensional bound-state-in-the-continuum metasurface, fabricated via aluminum-based lithography on 8-inch wafers. As a result, it achieves lattice-independent peak sensitivity exceeding 10 ³  %/RIU across the visible, near-infrared, and short-wave infrared regimes, an order of magnitude improvement over conventional refractometric biosensors. Integrated into a point-of-care testing system, this handheld, diode-driven Q -switching sensing platform enables rapid detection of small extracellular vesicles at concentrations as low as 24 attomolar, offering a 10 ⁴ -fold sensitivity enhancement over the mainstream ELISA for postoperative lung cancer monitoring. Grounded in Q -switching physics, this strategy offers a scalable, high-performance biosensing platform for portable diagnostics in clinical, remote, and at-home settings.