On-Column Surface-Enhanced Raman Spectroscopy Detection in Capillary Electrophoresis Using Running Buffers Containing Silver Colloidal Solutions

Abstract

Direct on-column surface-enhanced Raman spectroscopy (SERS) detection is demonstrated in capillary electrophoresis (CE). Distinctive SERS spectra of two test compounds, riboflavin and Rhodamine 6G, are obtained in 100 microm i.d. fused-silica capillaries under CE conditions using running buffers that contain silver colloidal solutions. Detection is performed using an unmodified commercial Raman spectrometer in a confocal microscope mode of operation. The effects of laser power, wavelength, spectra acquisition time, silver colloidal concentration, and applied voltage (i.e., flow rate) on the quality of SERS spectra are evaluated. Using laser powers of 17 mW (at the sample) at 515 nm and employing 1 s spectral acquisition times, spectra with bands exhibiting signal-to-noise ratios greater than 10 could be obtained for 1.0 x 10(-6) M riboflavin and very low nanomolar concentrations of Rhodamine 6G. This was accomplished without optimization of silver colloidal solution compositions and by using a low-throughput spectrometer. Incorporation of the colloidal solutions into running buffers is shown to have little effect on the separation of the test compounds as monitored using a laser-induced fluorescence instrumental scheme. However, SERS spectra degrade if the capillary is not rinsed between experiments. Riboflavin and Rhodamine 6G spectra are obtained on-the-fly for actual CE separations. In the case of the latter solute, the injected quantity was approximately 90 amol.

Surface-Enhanced Raman Scattering: A Powerful Tool for Chemical Identification

“…The observed spectral pattern is also very similar to the reported data. 61 The ready acquisition of Raman spectra for small amounts of substances of biological importance like riboflavin is very promising, particularly because it takes part in energy production by aiding in the metabolism of fats, carbohydrates, and proteins, and also because vitamin B2 is necessary for red blood cell formation, respiration, and antibody production, as well as for regulating human growth and reproduction.…”

Recent advances in the study of biomolecular interactions by capillary electrophoresis

“…The major drawback is still the low capacity of standard CE systems, equipped with UV detectors to yield specific information about sample components. CE coupled with other detectors, such as CE-MS [132,151], CE-inductively coupled plasma (ICP)-MS [152,153], CE-NMR [154,155], CE-FTIR [156], CERaman [157,158], and CE-X-ray [159] is capable to provide more structural elucidation. At present, however, only the on-line MS technique has a sufficient detection sensitivity for structural identification.…”

Capillary Electrophoresis - Optical Detection Systems

“…Recently, we demonstrated for the first time on-column CE detection with surface enhanced Raman spectrometry (CE-SERS). [8] This was accomplished by including < 1 .O w/v% silver colloidal particles in the CE running buffer. The silver nanoparticles were formed by the simple reduction of silver nitrate with sodium citrate.…”

“…41 The effects of applied voltage, laser power and wavelength, column rinsing, and other parameters are presented in Ref. 8. The on-column approach is relatively straightforward but it can require carehl control of running buffer conditions and the columns must be rinse between each run.…”