Graphene-Based Chiral Metasurface for Generation of Tunable Circular Dichroism—Design and Sensor Applications

In this article, we have proposed a graphene-based 2-D chiral metasurface for the mid-infrared region. The chirality factor in terms of circular dichroism (CD) can be modulated by tuning the chemical potential of graphene. We have demonstrated our metasurface design in a reflection mode of operation. The structure consists of arc-shaped etched graphene patterns on a SiO2 substrate. CD of 0.85 with a chemical potential of 0.95 eV has been obtained for normal incidence. The CD value can be reduced to 0.30 just by tuning the chemical potential to 0.55 eV. We then exploited this CD factor for various sensing applications. We have shown that by tuning the CD, we can design a biosensor for the detection of hemoglobin concentration in human blood. A sensitivity of 2091.33 nm/RIU has been obtained for the detection of anemic conditions from the normal concentration of hemoglobin. We have also demonstrated that the same sensor design can be used for the detection of hazardous solvents such as chlorobenzene and trifluoroacetic acid (TFA). Finally, we have proposed a gas-sensing application considering hazardous gases like carbon dioxide and ethylene oxide for demonstration purposes. A maximum sensitivity of 6600 and 1250 nm/RIU has been reported for carbon dioxide and ethylene oxide.