Low‐Index‐Contrast Dielectric Lattices on Metal for Refractometric Sensing

This article reports refractometric sensing using two optical resonances of different types supported by TiO2 nanopillar arrays on a gold film, which can be exposed to aqueous or organic environments. One lattice resonance, with enhanced electric fields extending into the surrounding environment, can maintain a quality factor Q > 200 when the bulk refractive index of the surrounding environment varies in a large range from 1.33 to 1.58. This lattice resonance exhibits not only sharp transitions of reflected light intensity but also rapid phase changes. The other resonance is of plasmonic nature with electric fields localized on the metal surface. Small changes in the bulk refractive index or the adsorbate layer (thickness and index) can be detected, with sensitivity comparable to that of plasmonic counterparts. The present hybrid metal–dielectric platform is promising for applications requiring dielectric instead of metallic sensing surfaces. A hybrid metal–dielectric nanostructure consisting of low‐index‐contrast dielectric lattice on a gold film is proposed for refractometric sensing. This hybrid system supports two resonances: one lattice resonance with electric fields extending into the surrounding environment and one plasmonic resonance. The measured bulk and surface sensitivities are comparable to those of all‐plasmonic counterparts.