Hybrid plasmonic Bound State in the Continuum entering the zeptomolar biodetection range

TL;DR

This paper introduces a hybrid plasmonic Bound State in the Continuum in a 2D silver nanostructure that achieves ultra-high sensitivity in biosensing, reaching zeptomolar detection limits.

Contribution

It demonstrates the first hybrid BIC in plasmonic nanostructures with high Q-factor and strong field confinement, enabling ultra-sensitive biosensing.

Findings

Achieved zeptomolar sensitivity in biosensing.

Demonstrated high Q-factor hybrid BIC in plasmonic structures.

Enhanced near-field confinement in nanogaps.

Abstract

Optical Bound States in the Continuum are peculiar localized states within the continuous spectrum that are unaffected by any far-field radiation and intrinsic absorption, therefore possessing infinite mode lifetime and Q-factor. To date they have been widely studied in dielectric structures whereas their exploitation in lossy media, i.e. plasmonic nanostructures, still remains a challenge. Here, we show the emergence of a hybrid BIC state in a 2D system of silver-filled dimers, quasi-embedded in a high-index dielectric waveguide. The hybrid BIC onset is found to be highly dependent on the bare modes' spectral and spatial overlap, but particularly on the plasmonic field's intensity. By tailoring the hybridizing plasmonic/photonic fractions we select an ideal coupling regime for which the mode exhibits both, high Q-factor values and strong near-field enhancement tightly confined in the nanogap and a consequently extremely small modal volume. We demonstrate that this optical layout can be exploited in a proof-of-concept experiment for the detection of TAR DNA-binding protein 43, which outperforms the sensitivity of current label-free biosensing platforms, reaching the zeptomolar range of concentration.