Silicon-on-Glass Graphene-Functionalized Leaky Cavity Mode Nanophotonic Biosensor

Subwavelength silicon nanostructures are known to support highly localized resonant optical modes. These resonances are spectrally narrow with an electromagnetic near-field that extends significantly into the surrounding medium. Here, we demonstrate that leaky cavity mode resonances (LCMR) in periodic silicon nanowire arrays can serve as a platform for low-cost, label-free, and highly sensitive biosensing and establish a theoretical framework for the LCMR phenomenon that is consistent with experimental results. The sensors exhibit bulk refractive index sensitivities up to 213 nm/RIU. Moreover, by functionalizing the surface of silicon nanostructures with a graphene monolayer, such structures can be used to optically detect low-concentration surface adsorption events. The specific label-free detection limit using immunoglobulin G protein (IgG) is found to be on the order of 300 pM with an extracted maximum sensor resonance shift of 5.42 nm. This sensing platform holds significant promise for unraveling protein protein interactions and offers unique opportunities for implementation of laser sensing on a single silicon photonic chip.