Topological Engineering of Exceptional Points for Label‐Free Single‐Molecule Detection

Abstract The topological structures around exceptional points (EPs) exhibit enhanced sensitivity for label‐free biosensors. However, the challenge of modifying the intrinsic topology to increase EP biosensor sensitivity remains unresolved. Here, topologically engineered EPs are utilized in multilayered metal‐dielectric metamaterials to significantly enhance bio‐sensitivity in the near‐infrared region, achieved through analytically modified eigenvalue topology. The EPs are systematically implemented at forward reflectionless points, and the corresponding eigenvalue splitting scales topologically as the square root of both asymmetric reflection and perturbation strength. The forward reflected light undergoes multiple interferences and repetitive sampling of the target molecules, resulting in a highly sensitive spectral response to even trace perturbations. Besides, a steeper topology with more pronounced asymmetric reflection leads to a sharper response path and significantly enhanced sensitivity. A superior detection limit of 0.9 aM is achieved for streptavidin in the proof‐of‐concept experiments, and furthermore, single‐molecule detection of the epidermal growth factor receptor 2 (ErbB2) biomarker is achieved with a detection limit of 0.2 aM. This universal topological engineering of EPs opens a new avenue to enhance bio‐sensitivity based on a topological effect.