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

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 at the microparticle's equator. As the dielectric particle parks to hot spots on the plasmonic particle we observe frequency shifts that are enhanced by a factor of 4, consistent with a simple reactive model. Once optimized the enhancement by this mechanism should exceed several orders of magnitude, putting individual protein within reach. (C) 2011 American Institute of Physics. [doi:10.1063/1.3599584]