Hybrid photonic-plasmonic resonances for enhanced biodetection

01.01.2014, 00:00

Newsletter 7

Whispering-gallery-mode (WGM) biosensors use high-Q optical resonances to detect, from a red shift in an excited resonance, binding of molecules and particles. Achieving sensitive and specific detection of individual viruses, DNA and proteins is important for implementing next-generation (on-chip) clinical diagnostic assays. Recently we have theoretically analysed photonic-plasmonic coupling between a WGM resonator and plasmonic nanoparticles as a means to push the detection envelope. Crossing of photonic and plasmonic modes for closely tuned WGM and localized surface plasmon (LSP) resonances was demonstrated (see figure). Resulting blue and red shifts of resonances are in agreement with experimental observations and afford multiplexing opportunities. Furthermore, nanoparticle induced resonance shifts were shown to be greatest when the LSP resonances were detuned by half the plasmon linewidth from the WGM resonance. At this optimal detuning, reactive coupling is maximised, leading to large near-field enhancements. Binding of biomolecules within these hotspots further tunes the WGM resonance in proportion to the enhanced intensity. Larger frequency shifts upon biomolecular binding are hence achievable with hybrid photonic-plasmonic resonators, putting single molecule detection within reach.

Contact: frank.vollmer(at)mpl.mpg(dot)de
Group: Biophotonics and Biosensing (MPRG)
Reference: M. R. Foreman et al., Phys. Rev. A 88, 023831 (2013).