Surface enhanced Raman spectroscopy in microchip electrophoresis.

Coupling microchip capillary electrophoresis to surface enhanced Raman spectroscopy (MCE-SERS) combines the high separation power of capillary electrophoresis with the capability to obtain vibrational fingerprint spectra for compound identification. Raman spectroscopy is a structurally descriptive and label-free detection method which is particularly suited for chemical analysis because it is non-destructive and allows the identification of analytes. However, it suffers from poor sensitivity and sometimes even requires acquisition times far longer than the typical peak width of electrophoretic separations. The Raman intensity can be drastically improved if the analyte is brought into close proximity to nanostructured metal surfaces or colloids due to the surface enhancement effect. This paper presents a novel approach in the field of MCE-SERS on-line coupling. The key element of the developed glass microfluidic device is a dosing structure which consists of two side channels joining the MCE channel symmetrically after the electrophoretic separation of the analytes. The dosing channel supplies silver nanoparticles (Ag-NPs), to the separated electrophoretic zones which facilitates an on-the-fly recording of SERS-spectra of the separated compounds. The functionality of the MCE-SERS chip was evaluated by the analysis of a rhodamine model mixture within 90 s achieving RSD of migration times below 1.5%. The approach was successfully applied for the analysis of the food additive riboflavin in a barbecue sauce.