Deep-UV All-dielectric qBIC Metasurface for Refractive Index Sensing

Abstract

All-dielectric metasurfaces supporting quasi-bound states in the continuum (qBICs) have emerged as powerful platforms for biosensing, yet their operation remains largely concentrated in the visible and near-infrared regimes. Extending these resonances into the deep-ultraviolet (DUV) to probe the intrinsic electronic absorption of biomolecules presents substantial material and nanofabrication challenges. Here, we experimentally demonstrate a hafnium dioxide (HfO${}_2$) metasurface supporting DUV qBICs in the wavelength range from 225 nm to 340 nm with quality factors reaching 500. We further demonstrate its refractive index sensing capabilities through integration with a microfluidic cell and optical characterization in reflection mode. We show that the introduction of an aqueous buffer leads to a further quality factor enhancement. Achieving a sensitivity of up to approximately 60 nm/RIU and an operational figure of merit of 40 ${\mathrm{RIU}}^{-1}$, this low-loss HfO${}_2$ metasurface provides a robust foundation for label-free DUV biosensing.