Dark‐State Guided‐Mode Resonance Sensors: Engineering Miniature Sensing Platforms

Abstract The guided‐mode resonance biosensor is first demonstrated experimentally ≈25 years ago. In traditional use, it operates at the bright edge of the leaky stopband with a resonance that is readily stimulated by a plane wave or a near‐planar wavefront. To expand the applicability and utility of this primary concept, a fundamentally new sensing paradigm is presented that exploits the inherent angular spectrum of focused Gaussian beams to excite the dark edge of the leaky stopband. The angular components of the Gaussian beam naturally break the local symmetry of the resonance lattice, enabling efficient coupling to quasi‐bound states in the continuum (quasi‐BIC) modes. This mechanism generates sharp resonance peaks sensitive to refractive index changes in the sensor host medium as well as to any adhered biolayers. The concept is validated through a modified rigorous coupled‐wave analysis (RCWA) framework that accounts for Gaussian beam angular decomposition, confirming robust resonance excitation across practical beam diameters (0.05–0.5 mm). Experimental proof‐of‐concept is demonstrated using a penny‐sized, 128‐microcell integrated sensor array, where focused Gaussian beams (0.3 mm wide) achieve 200 nm RIU −1 sensitivity in detecting aqueous solutions. The methodology opens innovative pathways for simplified, high‐throughput biosensing architectures integrated on compact sensing platforms.