Dual-channel metasurfaces for refractometric and spatial heterogeneity sensing

Nanophotonic sensors amplify analyte-induced optical signals through resonantly enhanced light-matter interactions. While effective for refractometric sensing, conventional sensing platforms typically collapse spatial variations in analyte distributions into ensemble-averaged readouts, thereby obscuring local heterogeneity. Here we present a dual-channel metasurface sensor capable of detecting both net analyte loading and nanoscale spatial inhomogeneity at deep-subwavelength scales. The device supports two distinct high-Q modes with deeply structured near-field profiles of opposite parity. Their complementary modal responses decouple analyte perturbations into bulk and differential components, which are encoded into two spectrally resolvable channels. We demonstrate these sensing modalities across analyte configurations exhibiting diverse forms of nanoscale heterogeneity, achieving a refractometric sensitivity of 357 nm/RIU and inhomogeneity detection below λ/10. This dual-channel capability, which extends nanophotonic sensing from analyte quantity to its spatial variation, opens a new avenue for multidimensional analysis of biological and material systems.