Integrated microsystems for micro capillary electrophoresis of DNA

The application of MEMS technology to the fabrication of biotechnology analytical tools has received particular attention in the past few years due to three major reasons: decrease of the required analyte volume, reduction of the analysis time, and the potential of integrating additional components on a single chip. Electrophoresis is the motion (separation) of charged molecules (of different mobility) under an electric field. This is a standard techniques used to separate between different fragment sizes in DNA analysis. Utilizing micro capillary electrophoresis (MCE) systems on a chip reduces chemical consumption and permits the application of a larger electric field for faster separation. This dramatically reduces the cost and time of each assay. In most MCE systems, with standard injection and separation microchannels, external electrodes and sensors are used to drive and detect the charged molecules. The application of MEMS technology to fabricate MCE systems allows the on-chip integration of these elements. In this work, a MCE system integrated with feed-through driving platinum electrodes was designed and fabricated using a newly developed glass-to-silicon bonding technology. The successful integration of the metal electrodes enables the integration of on-chip sensors as well. The integrated MCE system has been applied to measure the mobility and diffusion coefficient of small DNA fragments in different concentrations of agarose gel and hydroxyethylcellulose (HEC) polymer solution. The measured values were found to be in good agreement with published data for standard slab gel and polymer solution electrophoresis. Attractive geometrical features, bends and branches, were incorporated into the separation microchannel to investigate the DNA motion through such sections. The effect of a bend on the DNA plug band broadening can be described utilizing the concept of an equivalent length. Furthermore, a simple kinematic relationship was formulated predicting the DNA mass fraction injected into several downstream branches from a single upstream channel. These results provide a way to quantify the effects of the geometrical features that, thus far, were analyzed qualitatively. Micro capillary electrophoretic separation was demonstrated. A DNA sample containing two different sized DNA molecules was successfully separated into two distinct bands with the MCE system