Design of anapole mode electromagnetic field enhancement structures for biosensing applications.

Laaya Sabri,Jui-Nung Liu,Qinglan Huang,Brian T. Cunningham

doi:10.1364/oe.27.007196

Laaya Sabri, Jui-Nung Liu + Show 2 more

Open Access

https://doi.org/10.1364/oe.27.007196

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Abstract

The design of an all-dielectric nanoantenna based on nonradiating "anapole" modes is studied for biosensing applications in an aqueous environment, using FDTD electromagnetic simulation. The strictly confined electromagnetic field within a circular or rectangular opening at the center of a cylindrical silicon disk produces a single point electromagnetic hotspot with up to 6.5x enhancement of |E|, for the 630-650 nm wavelength range, and we can increase the value up to 25x by coupling additional electromagnetic energy from an underlying PEC-backed substrate. We characterize the effects of the substrate design and slot dimensions on the field enhancement magnitude, for devices operating in a water medium.

Highlights

Typical surface-based fluorescence assays for detection of protein or nucleic acid molecules for applications that include disease diagnostics [1], genome sequencing [2,3], and pathogen sensing [4] are performed upon glass or plastic surfaces, a variety of nanostructured optical surfaces have demonstrated the ability to increase detected photon output through the mechanisms of enhanced excitation, directional emission and reduced fluorescence lifetimes [5,6,7,8,9]
While anapole mode structures have been described in a variety of configurations [91,92,93,94], here we focus on the design, optimization, and achievable field enhancement performance for biosensing applications, where the device surface would be covered in aqueous media, and the enhanced fields are used to excite fluorescent dye molecules attached to biomolecules, with excitation wavelengths in the visible spectrum
We consider the utilization of the anapole mode nanoantenna structure in the context of exciting fluorescent emitters used to label nucleic acid and protein biomolecular interactions

Summary

Introduction

Typical surface-based fluorescence assays for detection of protein or nucleic acid molecules for applications that include disease diagnostics [1], genome sequencing [2,3], and pathogen sensing [4] are performed upon glass or plastic surfaces, a variety of nanostructured optical surfaces have demonstrated the ability to increase detected photon output through the mechanisms of enhanced excitation, directional emission and reduced fluorescence lifetimes [5,6,7,8,9] Such structures include plasmonic gratings, nanoantennas, and photonic crystals (PC) [10,11,12,13], which are each capable of efficiently coupling incident light from a laser into surface-confined resonant electric fields (enhanced excitation). Our analysis does not consider independent enhancement mechanisms that may occur due to the Purcell effect or due to enhanced collection efficiency into light collection optics, whose effects are known to multiply with enhanced excitation [89,90]

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