High-Sensitivity Photonic Crystal Biosensors using Topological Light Trapping

TL;DR

This paper demonstrates highly sensitive photonic crystal biosensors utilizing topological light trapping, achieving significantly improved detection sensitivity for analyte binding through defect-mediated optical tunneling and mode hybridization.

Contribution

It introduces a novel design of photonic crystal biosensors with topological domain-wall defects that greatly enhance sensitivity compared to previous designs.

Findings

Sensitivity improved by nearly 16 times over previous designs

Can distinguish three analyte-bindings simultaneously in a single measurement

Achieves biosensor sensitivity of nearly 3000 nm/RIU to thin analyte layers

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.