Localized surface plasmon resonances of metallic nanoparticles can be used for biosensing because of their sensitive dependence on the refractive index of the surrounding medium. The binding of molecules to the particles causes a change of the effective refractive index in their close vicinity, which leads to a reversible shift of the resonance. We present simulations and sensing experiments of a plasmon resonance based biosensor that makes use of the narrow antisymmetric resonance in coupled plasmonic vertical dimers. The sensitivity of the antisymmetric resonance is compared with that of a surface lattice resonance for refractive index sensing of bulk and of thin layers of molecules. The functionality of such a sensor surface is demonstrated via a testosterone immunoassay for detection of antibody from a solution by binding to surface-immobilized antigen in a fluidic channel.
Keywords: Biosensing; Label-free immunoassay; Plasmonic nanostructures; Testosterone; Vertical dimer.