Self-assembly-based photonic crystal slabs for refractive index sensing via bound states in the continuum

Abstract Bound states in the continuum (BICs) have drawn extensive attention in optics and photonics due to their ultrahigh quality (Q) factors, which make them ideal for high-sensitivity sensing applications. Existing approaches to realize BIC-supporting nanostructures in the optical regime often rely on expensive and complex fabrication methods such as electron beam lithography. Here, we propose a self-assembly-based method to fabricate photonic crystal (PhC) slabs working in the optical regime. In the fabricated PhC slab, the symmetry-protected BIC was directly observed. By integrating the PhC slab into a microfluidic chip, we characterized the related quasi-BIC mode and demonstrated its sensing performance in various concentrations of NaCl solutions, achieving a sensitivity of 110 nm / RIU .