Toroidal Dipole-Integrated Graphene Metasurfaces for Ultrasensitive Detection of Amino Acids

Terahertz (THz) metasurface biosensors represent an emerging interdisciplinary technology that exhibits exceptional sensitivity in detecting minute quantities of specific substances. Toroidal dipole (TD) resonances in metamaterials also offer a platform to probe strong light–matter interactions in its proximity due to the nonradiating confinement of photons, which results in strong field confinement for enhanced sensing of the analytes. However, in natural materials, the presence of electric and magnetic dipoles (MDs) hinders the detection of TDs, making it challenging to study experimentally. Hence, this study proposes a metasurface biosensor grounded on the Dirac point and incorporating a TD, specifically designed for the detection of tyrosine and arginine. Notably, the inclusion of graphene and the
$\pi $
–
$\pi $
stacking effect, particularly evident in tyrosine, significantly enhances the sensor’s detection limit. Consequently, the sensor achieves an outstandingly low detection limit of 26.43 fg/mL, whereas the detection limit for arginine was only 581.4 fg/mL. This highlights the paramount importance of combining graphene and TD metasurfaces in achieving the detection of extremely low concentrations.