Citation: Jing, Z.; Jiaxian, W.; Lizhen,
G.; Weibin, Q. High-Sensitivity
Sensing in All-Dielectric Metasurface
Driven by Quasi-Bound States in the
Continuum. Nanomaterials 2023, 13,
505. https://doi.org/10.3390/
nano13030505
Academic Editors: Ki-Hyun Kim and
Deepak Kukkar
Received: 30 December 2022
Revised: 15 January 2023
Accepted: 19 January 2023
Published: 27 January 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
High-Sensitivity Sensing in All-Dielectric Metasurface Driven
by Quasi-Bound States in the Continuum
Zhao Jing
1
, Wang Jiaxian
1,
*, Gao Lizhen
1
and Qiu Weibin
2
1
Computer Science and Information Engineering School, Xiamen Institute of Technology,
Xiamen 361021, China
2
College of Information Science and Engineering, Huaqiao University, Xiamen 361021, China
* Correspondence: wangjx@hqu.edu.cn
Abstract:
Quasi-bound states in the continuum (quasi-BIC) in all-dielectric metasurfaces provide a
crucial platform for sensing due to its ability to enhance strong matter interactions between light-
waves and analytes. In this study, a novel high-sensitivity all-dielectric sensor composed of a
periodic array of silicon (Si) plates with square nanoholes in the continuous near-infrared band is
theoretically proposed. By adjusting the position of the square nanohole, the symmetry-protected BIC
and Friedrich–Wintgen BIC (FW–BIC) can be excited. The torodial dipole (TD) and electric quadruple
(EQ) are demonstrated to play a dominating role in the resonant modes by near-field analysis and
multipole decomposition. The results show that the sensitivity, the Q-factor, and the corresponding
figure of merit (FOM) can simultaneously reach 399 nm/RIU (RIU is refractive index unit), 4959, and
1281, respectively. Compared with other complex nanostructures, the proposed metasurface is more
feasible and practical, which may open up an avenue for the development of ultrasensitive sensors.
Keywords:
all-dielectric metasurface; Fano resonance; torodial dipole; bound state in the continuum;
refractive index sensing
1. Introduction
Metasurface is an artificially arranged array of periodic subwavelength structures with
unusual electromagnetic characteristics, such as negative refractive index [
1
], near-zero
refractive index [
2
], and negative magnetic permeability [
3
]. With the development of
micro-nano processing technology, metasurfaces are widely used in metalens [
4
], light
absorbers [
5
], biochemical sensors [
6
], and optical modulators [
7
]. Compared with three-
dimensional (3-D) structures, photonic crystals, or metal resonators, dielectric supersur-
faces with high Q-factor have advantages in terms of flexibility, size, and nonlinear opti-
cal compatibility [
8
–
10
]. The all-dielectric metasurface supports Mie resonance and can
provide high Q-factor and FOM (Figure of Merit), and is more compatible with comple-
mentary metal oxide semiconductor production processes [
10
–
12
]. Therefore, all-dielectric
metasurface-based sensors exhibit stronger light-harvesting capabilities and smaller vol-
umes, enabling label-free, on-chip integration, and ultrasensitive sensing, which become
current research hotspots. In 2020, Jeeyoon et al. presented a metasurface structure com-
posed of an all-dielectric hollow cuboid array, which can be used for refractive index
sensing with a maximum sensitivity of 161 nm/RIU and a FOM of 78 [
13
]. In 2021, Zhang
et al. suggested a “lucky junction”-shaped all-dielectric nanostructure that is insensitive to
polarization and incident angle, with a sensitivity of 986 nm/RIU and a FOM of 32.7 [
14
].
In 2022, Song et al. proposed a refractive index sensor composed of two asymmetric rect-
angular hollow silicon cylinders, with a maximum sensitivity of 160 nm/RIU and a FOM
of 575 [15].
The idea of bound states in the continuum (BIC) has been included into various
metasurface designs in order to achieve higher Q resonances [
16
–
21
]. BIC designates a
Nanomaterials 2023, 13, 505. https://doi.org/10.3390/nano13030505 https://www.mdpi.com/journal/nanomaterials
