Indirect fluorescence detection of simple sugars via high-pH electrophoresis in poly(dimethylsiloxane) microfluidic chips

This article describes the successful electrophoretic separation of simple carbohydrates in a polymeric microfluidic chip. The device fabricated in poly(dimethylsiloxane) (PDMS) is found to be stable in high-pH solutions. This allows sugars to be separated electrophoretically at pH values at or above their pK(a) using indirect fluorescence detection. Signal-to-noise values greater than 10:1 were obtained using a mercury arc lamp excitation source and a fluorescein-containing mobile phase for the detection of sugars at concentrations as low as 5 mM. The results obtained compare favorably with published results for the same system using a traditional fused-silica capillary. Analysis of the data revealed a significant experimental sensitivity of the migration times measured in these PDMS devices, an aging effect that leads to considerable systematic drift over the course of a series of replicate measurements. These experiments highlighted the importance of the surface chemistry of PDMS, especially as it pertains to its ability to support stable electroosmotic flow within the separation device. Channel priming at high pH provides a necessary, but by itself insufficient, means by which this instability can be minimized.