Biomarker detection using GST-based permittivity-asymmetric metasurface

Non-invasive detection of biomarkers can help in the early screening of lethal diseases, such as cancer and Alzheimer's. In this paper, we present a numerical study of a high-quality resonant permittivity-asymmetric metasurface that offers tunability in the mid-infrared range by employing the phase change property of Germanium Antimony Telluride, Ge3Sb2Te6 (GST326). In this approach, we used dissimilar materials of ellipse-shaped nanopillars, and shifted the nanopillars from their center positions to break the symmetry-protected bound state and generate a high-Q resonance sufficient for detecting trace amounts of analytes. The peak location of the resonance can be controlled by tuning the crystallization state of GST326 for broadband retrieval of analyte signatures. We performed a grid search to optimize the design parameters to obtain a tuning range that matches the absorption band of amide I and II groups. As a proof of concept, we demonstrate sensing of a thin protein layer using the proposed metasurface and we show how our structure is sensitive to the imaginary part of the analyte refractive index and how the permittivity-asymmetry resonance is robust against crystallization losses. We also propose a layout for a practical device that can be used for biomarker detection applications.