High-Sensitivity Photonic Crystal Biosensors using Topological Light Trapping
Abstract
Photonic crystals (PCs) with localized optical cavity modes arising from topological domain-wall line defects are simulated for optical biosensing by numerical solution of Maxwell's equations. These consist of a square lattice of square silicon blocks with a significant photonic band gap (PBG). Optical transmission through the PBG at specific frequencies occurs by defect-mediated optical tunneling. Biofluid flows perpendicular to light propagation, through a channel containing the PC, defined by silica side-walls and an underlying silica substrate. Replacing the silicon blocks with thin silicon strips throughout the domain-wall region, analyte binding coincides with regions of maximal field intensity. As a result, the sensitivity is improved by almost 16 times higher than the previous designs. We analyze optical mode hybridization of two nearby domain walls and its close relation to the transmission-levels and correlations in frequency shifts of nearby optical resonances in response to analyte-bindings. We illustrate three high-sensitivity chips each with three domain-wall defects, all of which can distinguish three analyte-bindings and their combinations completely in a single spectroscopic measurement. In a photonic crystal, consisting of silicon squares embedded in a water background and a 5-micron lattice spacing, the biosensor sensitivity to a thin analyte binding layer is nearly 3000 nm/RIU, and to the overall background biofluid is over 8000 nm/RIU.
Cite
@article{arxiv.2508.04321,
title = {High-Sensitivity Photonic Crystal Biosensors using Topological Light Trapping},
author = {Zhengzheng Zhai and Sajeev John},
journal= {arXiv preprint arXiv:2508.04321},
year = {2026}
}