Abstract
Metallic nanostructures including single and double nanodisks are successfully used to enhance the localized electric field in vicinity of microcavity in whispering gallery mode (WGM) sensor. We demonstrate numerical calculations of plasmonic coupling of WGMs to single and double nanodisk arrays on a planar substrate. We then experimentally confirmed that the resonance wavelength of WGM sensor was dramatically shifted by adoption of single and double nanodisks on the surface of microcavity in the WGM sensor. Thus, our approach provides the tunable sensitivity of WGM sensor, and has a great potential to be used in numerous areas where the single biomolecule, protein-protein folding and biomolecular interactions are involved.
Highlights
A Whispering gallery mode (WGM) biosensor has been a well-defined emerging technique for label-free detection of biomolecules, their conformations and interactions[1,2,3,4,5,6,7]
Any mechanism that can increase the field intensity at the binding site without significantly degrading the Q-factor of the whispering gallery mode (WGM) resonance will produce an enhancement in the wavelength shift, thereby enhancing the detection sensitivity
We tested for the fraction of WGM fields that are localized upon coupling to the plasmonic nanodisk structure by observing WGM resonance wavelength shifts as a function of coupling and decoupling to the antenna
Summary
A Whispering gallery mode (WGM) biosensor has been a well-defined emerging technique for label-free detection of biomolecules, their conformations and interactions[1,2,3,4,5,6,7]. A red-shift of the resonance wavelength occurs upon analytical binding since bound molecule produces slight increase in optical path length. For this reason, the WGM biosensor has been employed for ultrasensitive detection with a detection limit down to the single virus and possibly the single molecular level[6]. Any mechanism that can increase the field intensity at the binding site without significantly degrading the Q-factor of the WGM resonance will produce an enhancement in the wavelength shift, thereby enhancing the detection sensitivity. Metallic nanostructures on chip provide ideal platforms to study the effect of plasmonic field localization in WGM biosensing. We experimentally estimate and compare the energy fraction of the WGMs fields that localized at the single and double nanodisk arrays
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