What is surface enhanced Raman scattering, or SERS?

Surface enhanced Raman scattering (SERS) is a technique which offers orders of magnitude increases in Raman intensity, overcoming the traditional drawback of Raman scattering – its inherent weakness.  Enhancement factors can be as high as 1014-15, which are sufficient to allow even single molecule detection using Raman.  SERS is of interest for trace material analysis, flow cytometry and other applications where the current sensitivity/speed of a Raman measurement is insufficient.

The enhancement takes place at a metal surface which has nanoscale roughness, and it is molecules adsorbed onto that surface which can undergo enhancement.  Typical metals used are gold or silver – preparation of the surface can be through electrochemical roughening, metallic coating of a nano-structured substrate, or deposition of metallic nanoparticles (often in a colloidal form).  Many researchers create their own SERS substrates, but commercially available kits offer a more routine approach.

Practically, the advantages of SERS can be explored on any Raman system, and the actual measurement is made in the standard way. Typically it is necessary to use a laser wavelength which is compatible with the chosen SERS metal, but beyond this there are no major difficulties.  SERS spectra do sometimes differ from a ‘normal’ Raman spectrum of the same material, so interpretation of data must be considered.

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