Plasmon-enhanced single molecule detection with optical microcavities

Label-free detection of single molecules has been a dream of biologists and biotechnologists. We have come one step closer towards achieving this goal by coupling optical resonators to nanoplasmonic structures. We use whispering gallery modes (WGM) in optical microsphere resonators to excite plasmon resonances in gold nanorods. Strong electromagnetic field enhancements are observed at the nanoparticle site - without significant losses to the quality factor of the resonator. When a molecule binds to the hotspot location it tunes the resonance frequency in proportion to the encountered field strength. The hotspots can provide large sensitivity enhancements – bringing label-free single molecule detection within reach. Here, we will investigate the physics of single molecule detection with plasmon enhanced microcavities, an endeavour that is essential for designing the next generation of biosensors and to elucidate intricate mechanisms of molecular machines.