Non-aqueous microchip electrophoresis for characterization of lipid biomarkers

Abstract

In vivo measurements of lipid biomarkers are hampered by their low solubility in aqueous solution, which limits the choices for molecular separations. Here, we introduce non-aqueous microchip electrophoretic separations of lipid mixtures performed in three-dimensional hybrid nanofluidic/microfluidic polymeric devices. Electrokinetic injection is used to reproducibly introduce discrete femtolitre to picolitre volumes of charged lipids into a separation microchannel containing low (100 μM-10 mM) concentration tetraalkylammonium tetraphenylborate background electrolyte (BGE) in N-methylformamide, supporting rapid electro-osmotic fluid flow in polydimethylsiloxane microchannels. The quality of the resulting electrophoretic separations depends on the voltage and timing of the injection pulse, the BGE concentration and the electric field strength. Injected volumes increase with longer injection pulse widths and higher injection pulse amplitudes. Separation efficiency, as measured by total plate number, N, increases with increasing electric field and with decreasing BGE concentration. Electrophoretic separations of binary and ternary lipid mixtures were achieved with high resolution (R s ∼ 5) and quality (N > 7.7 × 10(6) plates m(-1)). Rapid in vivo monitoring of lipid biomarkers requires high-quality separation and detection of lipids downstream of microdialysis sample collection, and the multilayered non-aqueous microfluidic devices studied here offer one possible avenue to swiftly process complex lipid samples. The resulting capability may make it possible to correlate oxidative stress with in vivo lipid biomarker levels.