Homogeneous and Significant Near‐Field Enhancement in All‐Dielectric Metasurfaces for Sensing Applications

Abstract All‐dielectric metasurfaces supporting high‐Q resonances have emerged as a promising platform for sensing applications. However, the greatly enhanced near‐fields are usually confined within the all‐dielectric nanostructures rather than the outside analyte region, severely limiting the bulk sensitivity and the biosensing performance. Here, a silicon metasurface formed by the hybridization of two lattices with a relative displacement is designed to support nonlocal quasi‐bound states in the continuum (q‐BICs) featuring homogeneous and significant near‐field enhancement over large volumes outside the silicon nanodisks. A high bulk sensitivity of 407 nm RIU^–1 is experimentally demonstrated for the refractive index sensing applications, and a limit of detection down to 20 pg mL^–1 for a protein biomarker for the early‐stage breast cancer screening, which is improved by more than an order of magnitude over the state of the art. It is expected that the nonlocal q‐BICs open new opportunities for realizing greatly enhanced light–matter interactions over large volumes in applications beyond biochemical sensing.