Ultrasensitive Refractive Index Sensing Based on the Quasi-Bound States in the Continuum of All-Dielectric Metasurfaces

Hui Hsin Hsiao*, Yi Chien Hsu, Ai Yin Liu, Jou Chun Hsieh, Yu Hsin Lin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


Symmetry-protected quasi-bound states in the continuum (BIC) controlled by metasurfaces with broken in-plane symmetry are widely exploited to achieve highly surface-sensitive and spectrally sharp resonances for nanophotonic biosensors. Through the engineering of silicon-based asymmetric nanobar pairs, a quasi-BIC mode is excited showing a dominant toroidal dipole (TD) and electric quadrupole (EQ) resonant feature in the near-infrared and performs ultrahigh sensitivity in the refractometric monitoring of local environment changes. Contrary to the typical electric and magnetic Mie-type resonances of dielectric resonators with the enhanced field mostly inside the resonator volume, the TD-EQ quasi-BIC mode is found to exhibit strong and tightly confined optical fields at the surface of tilted nanobar pairs, and its refractive-index (RI) sensitivity can be dramatically increased for nanopillars with larger aspect-ratio. The measured (simulated) sensitivity and figure of merit for nanobar pairs with a height of 450 nm reach 608 nm/RIU and 46 (612 nm/RIU and 85), respectively. Such ultrahigh sensitive all-dielectric platform can be fabricated through complementary metal-oxide-semiconductor compatible process and is promising for on-chip integration and sensor miniaturization to a wide range of diagnostic applications.

Original languageEnglish
Article number2200812
JournalAdvanced Optical Materials
Issue number19
Publication statusPublished - 2022 Oct 4


  • bound states in the continuum
  • dielectric metasurfaces
  • electric quadrupole
  • refractive-index sensing
  • toroidal dipole

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics


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