We have developed a microfabricated analytical device on a glass chip that performs a protein sizing assay, by integrating the required separation, staining, virtual destaining, and detection steps. To obtain a universal noncovalent fluorescent labeling method, we have combined on-chip dye staining with a novel electrophoretic dilution step. Denatured protein-sodium dodecyl sulfate (SDS) complexes are loaded on a chip and bind a fluorescent dye as the separation begins. At the end of the separation channel, an intersection is used to dilute the SDS below its critical micelle concentration before the detection point. This strongly reduces the background due to dye molecules bound to SDS micelles and also increases the peak amplitude by 1 order of magnitude. Both the on-chip staining and SDS dilution steps occur in the 100-ms time scale and are approximately 10(4) times faster than their conventional counterparts in SDS-PAGE. This represents a much greater speed increase due to microfabrication than has been obtained in other assay steps such as electrophoretic separations. We have designed and tested a microchip capable of sequentially analyzing 11 different samples, with sizing accuracy better than 5% and high sensitivity (30 nM for carbonic anhydrase).

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This paper presents experimental data, simulation tools (FlumeCAD), simulation results, and their use together to analyze and improve the designs of electrokinetic injection and switching components for microchemical fluidic systems.INTRODUCTION Electrokinetic microfluidic microsystems are powerful analytical tools for many applications, such as nucleic acid analysis, enzyme assays, and immunoassays [ 1-61. Such systems have gained considerable importance as components in micron-scale integrated chemicaybiochemical analysis or synthesis systems, also referred to as lab-on-a-chip. The basic "unit process" operations in these systems are sample injection, mixing, chemical reaction or modification, separation, and detection. Assembling a system of many "unit process" nodes requires one or more transport mechanisms to move sample and reagents through the "wires" of the system. Many of these systems rely on electrokinetic physics as their transport mechanism, although pressure and pneumatic applications have also been demonstrated. Complicated relationships exist between the microchannel geometries, the conditions under which the devices operate, and the behavior of the multicomponent fluids transported in these channels. In the past researchers have been forced to use costly trial and error methods to understand and design such microfluidic systems.CAD tools can be a valuable aid in the design of microfluidic systems. Numerical analyses provide significant insight into the fluid mechanics in these systems. They allow the extraction of material and flow properties that are generally not well documented, or that vary from application to application or from one manufacturing technology to another. Furthermore such tools help the designer to explore a much larger space of designs than is easily available from experiment, and do so in a quantitative way which enables the extraction of key parameters for improved or optimal operation of common microchemical system components.In this paper we include experimental data from some electrokinetic injection and switching components, as well as matching simulations of those components.We then demonstrate the use of the simulation tools to generate virtual experiments to help the designer choose good or optimal settings for the pinch field during injection and good or optimal settings for the switching field in a switch component.The simplest switching component is an intersection of two channels. Such intersections are surprisingly powerful tools that enable the definition of sample plugs at the picoliter level [2]; this in turn allows microfabricated electrokinetic systems to outperform their conventional counterparts by orders of magnitude [3]. The switching components are employed in separation and dispensing systems to inject the sample from the load channel to the separation channel. A typical system employing such switching components is presented in Figure 1, showing a microfluidic system fabricated by etching and bonding in glass.The parameters that determine optimal inje...