Ultrasensitive Mid‐Infrared Biosensor Created by Graphene‐Driven Gold Metasurface: Theoretical Insight

ABSTRACT This study theoretically proposed an ultrasensitive mid‐infrared biosensor named graphene‐driven gold metasurface, generating strong quasi‐bound states in the continuum (QBIC) resonant model. The graphene‐driven gold metasurface was composed of a periodically arranged array of units, and each array unit (3 µm) was designed by stacking various thicknesses of graphene layers within the gap of two parallel gold pillars onto a plasmonic gold film (0.1 µm). Via modulating the relative height ratio (h 1 /h 2 ) between the height (h1) of two gold pillars and the thickness (h 2 ) of graphene layers, the strong QBIC resonant was excited. As the geometric asymmetry was 3, the graphene‐driven gold metasurface can provide a high quality factor (Q‐factor) of 739, achieving an ultra‐high detection sensitivity of 37.8 THz/RIU (refractive index unit, RIU). For a tiny refractive index variation in the targeted analyte layer, our proposed biosensor exhibited an excellent linear response and a theoretical limit of detection of 2 × 10 −4 RIU. Using sperm cells as targeted analytes, two linear correlation curves, including resonance frequency vs. refractive index and resonance frequency vs. concentration, were established, enabling to perform detection of sperm cells as low as 10 3 cells per milliliter. Our proposal suggested that the graphene‐driven gold metasurface could offer a possible pathway for screening reproductive health.