Polyacrylamide gel plugs enabling 2-D microfluidic protein separations via isoelectric focusing and multiplexed sodium dodecyl sulfate gel electrophoresis

In situ photopolymerized polyacrylamide (PAAm) gel plugs are used as hydrodynamic flow control elements in a multidimensional microfluidic system combining IEF and parallel SDS gel electrophoresis for protein separations. The PAAm gel plugs offer a simple method to reduce undesirable bulk flow and limit reagent/sample crosstalk without placing unwanted constraints on the selection of separation media, and without hindering electrokinetic ion migration in the complex microchannel network. In addition to improving separation reproducibility, the discrete gel plugs integrated into critical regions of the chip enable the use of a simple pressure-driven sample injection method which avoids electrokinetic injection bias. The gel plugs also serve to greatly simplify operation of the spatially multiplexed system by eliminating the need for complex external fluidic interfaces. Using an FITC-labeled Escherichia coli cell lysate as a model system, the use of gel plugs is shown to significantly enhance separation reproducibility in a chip containing five parallel CGE channels, with an average variance in peak elution time of only 4.1%.