Sensitive biodetection in flow using metasurface hosting quasi-bound state in the continuum resonances

TL;DR

This paper presents a novel optical metasurface biosensor utilizing quasi-bound state in the continuum resonances for highly sensitive, real-time detection of biomolecular interactions in flow, suitable for point-of-care diagnostics.

Contribution

The design of a metasurface hosting high-Q q-BIC resonances with enhanced sensitivity for flow-based biosensing is a key innovation of this work.

Findings

Refractive index sensitivities > 315 nm/RIU

Real-time detection of streptavidin-biotin binding

Limit of detection of 1.8x10^-8 M

Abstract

We have designed optical metasurfaces hosting high-quality factor quasi-bound state in the continuum (q-BIC) resonances for optical biosensing in flow. The unit cell of the metasurface contains two rectangular bars. An asymmetry factor is introduced by varying the gap width between the bars, to enable optical coupling to a q-BIC resonance confined to the air gap between neighboring nanoresonators. The location of the resonances makes them highly sensitive to changes in the local refractive index, leading to experimental bulk refractive index sensitivities exceeding 315 +/- 22 nm/RIU and a figure-of-merit of 66 +/- 5 RIU-1. Successful streptavidin-biotin binding was observed by measuring the metasurface transmission in real-time by exposing the metasurface to various concentrations of analytes via a commercial microfluidic flow cell apparatus. The experimental limit of detection, defined as 3{\sigma} above noise, was found to be 1.8x10-8 M. This platform represents a compact optical approach for point-of-care diagnostics with fast read-out.