Nanoplasmonics and surface enhanced spectroscopy

Optical configuration for integrated surface plasmon-coupled directional enhanced Raman scattering spectroscopy
 and SPR sensing
Beketov G.V.1, Shynkarenko O.V.1, Yukhymchuk V.O.1
1 V. Lashkaryov Institute of Semiconductor Physics, Natl. Acad. of  Sci. of Ukraine. Prospect Nauky, 41, Kyiv-03028, Ukraine. 
E-mail: gbeketov@ukr.net.

A novel optical arrangement for surface enhanced Raman spectroscopy (SERS) relying on the surface plasmon resonance (SPR) in flat planar metallic slabs is presented. Propagating surface plasmons were excited using the hemispherical total internal reflectance prism in the Kretschmann configuration. In this configuration, the Raman scattering radiation is directionally emitted inside the prism with the angular distribution in the shape of a hollow cone (the Kretschmann cone). The Raman spectra were acquired with the use of a modified elliptical mirror designed for collecting the light from the Kretschmann cone over a wide divergence range [1]. The proposed arrangement has no limitations on the relative aperture and can be employed for SERS measurements using standard spectroscopic systems. In addition, it is ideally suited for simultaneous functioning as the SPR sensor. Its efficiency is demonstrated using the Rhodamine 6G dye as a SERS reporter. Integration of SERS spectroscopy with the SPR analysis on this platform show great promise of evolving a surface-sensitive analytical technique with enhanced capabilities, especially in the fields of chemistry and biochemistry. 
Plasmon-coupled directional enhancement of R6G spectral bands was compared with SERS enhancement achieved with the use of nanoparticles and with the results of theoretical analysis of molecular vibrational spectra based on density functional theory calculations. Significant distinctions were revealed, presumably indicating that the surface selection rules for SERS [2] are not applicable to the directional enhanced Raman scattering spectroscopy. The most plausible reason for this lies in different polarization of evanescent electric fields associated with propagating and localized surface plasmons.

1.	Beketov G.V., Shynkarenko O.V. A device for surface-enhanced Raman spectroscopy // Pat. UA 121412 U – 2017.
2.	Moskovits M.  Surface selection rules // J. Chem. Phys.- 1982.-77.-P. 4408-4416.