Electrokinetic Instabilities and Sample Stacking
H. Lin, M.H. Oddy and J.G. Santiago
Stanford University, US
electrokinetics, microfluidics, electrophoresis, sample preconcentration
Microfabrication technology has enabled the application of electrokinetics as a method of performing chemical analyses and achieving liquid pumping in electronically-controlled microchip systems with no moving parts. This talk reviews progress at Stanford in the development of optimized field amplified sample stacking (FASS) for integration with on-chip capillary zone electrophoresis. FASS leverages conductivity gradients as a robust method of increasing sample concentration prior to electrophoretic separation. A major challenge to achieving robust, high-efficiency FASS is the role of electrokinetic instabilities (EKI) generated by a coupling of electric fields and ionic conductivity gradients. This coupling results in electric body forces in the bulk liquid that can generate temporal, convective, and absolute flow instabilities. Suppression and/or control of electrokinetic flow instabilities is critical as these conductivity-gradient-induced instabilities dramatically increase dispersion rates and thereby limit stacking efficiency. We have identified the key physical mechanisms involved in EKI; developed generalized models for heterogenous electrokinetic systems (applicable to both FASS and EKI); and validated these models with experiments. We have used our understanding of heterogenous electrokinetic systems to develop novel chip systems that can achieve signal increases of more than 12, 000 fold using FASS. This stacking ratio is over 100 times larger than previous on-chip FASS devices.
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Nanotech 2005 Conference Program Abstract