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N. Leopold, B. Lendl:
"On-column silver substrate synthesis and surface-enhanced Raman detection in capillary electrophoresis";
Analytical and Bioanalytical Chemistry, 396 (2010), 2341 - 2348.

A new, simple, and efficient approach for oncolumn
surface-enhanced Raman scattering (SERS) detection
in capillary electrophoresis (CE) is reported. A ∼50-μm
SERS substrate spot was prepared by laser-induced growth
of silver particles in the 100-μm inner diameter CE
capillary window or in a flow cell consisting of a 250-μm
inner diameter fused silica capillary connector. For this
purpose, the Raman laser was focused by a 20× objective
into the detection window filled with a 0.5 mM silver
nitrate and 10 mM citrate buffer solution. During the CE
runs, the silver substrate spot was formed in a few seconds
after the analyte injection, hence the analytes adsorbed
sequentially to the silver surface when the detection
window was reached, followed by desorption from the
silver surface and continuing the electrophoretic migration
to the capillary end. Thus, beyond migration time, valuable
molecular specific information was delivered by the SERS
spectra. Accurate separations and high-intensity SERS
spectra are shown by CE-SERS time-dependent 3D electropherograms
for the analytes rhodamine 6G, 4-(2-pyridylazo)
resorcinol (PAR), PAR complex with Cu(II) and
methylene blue at 0.25-25 ppm concentrations, by using
1.4-3.6 mW HeNe laser power and an acquisition time of
5 s for each spectrum. Before and after each analyte passes
the detection window, clean background spectra were
recorded and no memory effects perturbed the SERS
detection. The silver substrate is characterized by a fast
preparation rate, good reproducibility, a preparation success
rate of over 95% and no mentionable influence on the
electrophoretic migration time, the CE-SERS and CE-UV
electropherograms being in good agreement. The successful
coupling of CE and on-column SERS detection opens new
perspectives for monitoring CE separations.

http://dx.doi.org/10.1007/s00216-010-3468-3