Band folding unlocks high-density hidden modes for sub-terahertz cancer cell phenotyping

Abstract Metamaterial-based biosensors (meta-biosensors) offer a versatile platform for label-free detection of biological analytes. However, conventional multi-mode designs often rely on intricate configurations with uncertain mode excitability under free-space incidence. Here, we propose a band-folding-enabled meta-biosensor that supports high density of free-space- excitable modes. Guided by a Fourier-series theoretical framework developed to predict the coupling strengths, numerous symmetry-protected hidden modes are converted into radiative resonances by introducing perturbations into a hexagonal superlattice. We apply this multi- mode platform to phenotype different biological cells at sub-terahertz frequencies. Supported by histopathological validation, we demonstrate that the dense accumulation of intracellular biomass and enlarged nuclei in malignant cells induce a distinct volumetric permittivity contrast. This mechanism could enable rapid differentiation of cancerous phenotypes from the normal counterparts. Our work bridges metamaterial device physics with biological structural insights, broadening the horizon for mode-multiplexed metamaterials in phenotypic screening.