Selectively enhanced Raman/fluorescence spectrum in photonic-plasmonic hybrid structures

Manipulation of the interaction between molecules and photonic-plasmonic hybrid structures is critical for the application of the surface enhanced spectroscopy (SES). Here we report a study on the mode coupling mechanism and SES performance in a typical optoplasmonic system constructed by the polystyrene microsphere (PS MS) resonator and gold nanoparticles (Au NPs). The mode coupling is found closely depend on the relative positions of PS MS, Au NPs, and molecules in the optoplasmonic system, based on which manner selectively enhanced Raman and fluorescence signals of molecules can be realized via the collaboration of enhancement and quenching channels of the PS MS and Au NPs. We demonstrate two arrangements of the photonic-plasmonic hybrid structure which can support fluorescence signal with sharp whispering-gallery modes and apparently enhanced Raman signal with relatively low detection limit and good robustness, respectively.