Plasmonic enhancement of a whispering-gallery-mode biosensor for single nanoparticle detection in aqueous solution

We describe and demonstrate a physical mechanism that substantially enhances the label-free sensitivity of a Whispering-Gallery-Mode biosensor for the detection of individual nanoparticles in aqueous solution. It involves the interaction of dielectric nanoparticle in an equatorial carousel orbit with a plasmonic nanoparticle bound on the orbital path. As a 60 nm dielectric particle parks on plasmonic hot spots we observe frequency shifts that are considerably enhanced consistent with a simple reactive model. Using the same model the label free detection of a single bovine serum albumin (BSA) molecule is projected.