Tunable Van der Waal's optical metasurfaces (VOMs) for biosensing of multiple analytes

Van der Waal's heterostructure assembling low dimensional materials are the new paradigm in the field of nanophotonics. In this work, we theoretically investigate Van der Waal's optical metasurfaces consisting of graphene and hBN for the application of biosensing of multiple analytes in the mid-infrared (MIR) region. Phonon polaritons of hexagonal boron nitride (hBN) show an advantage over plasmon polaritons, as the phonon polaritons are lossless and possess high momentum and enhanced lifetime. The hybrid phonon mode produced at 6.78 µm in the mid-infrared (MIR) region with near-perfect absorption is used for surface-enhanced infrared absorption (SEIRA) based detection of organic analytes. Moreover, by adding the graphene layer, the device's overall resonance responses can be tuned, enabling it to identify multiple organic analytes-such as 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) and nitrobenzene (Nb) [C₆H₅NO₂], just by changing graphene's fermi potential (Ef). Owing to large wave vector of phonon polariton, the device has the capability to detect small amount of number of molecules (390 for CBP and 1990 for nitrobenzene), thus creating a highly sensitive optical biosensor.