TED-AJ03-406 TRANSPORT OF BIOMOLECULES IN THE RATCHETING ELECTROPHORESIS MICROCHIP (REM)

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The ratcheting electrophoresis microchip (REM) is a novel concept of a microfluidic device for electrophoretic separation of macromolecules such as DNA and proteins in aqueous solution. The device consists of a microchannel and an array of thousands of parallel linear microelectrodes with a pitch of ∿ 10 μm embedded in the wall of the microchannel. The controlled voltages of the microelectrodes generate electric field in the solution in the channel. In spite of the applied voltage of the electrodes as low as ∿ 1 V, strong electric field is formed in the solution. In the course of the electrophoretic migration of analyte molecules due to the electric field, the analyte molecules are aligned according to their mobility, and then, they are "ratcheted" with a programmed timing; a peak of electric potential is generated in the solution and the analyte molecules are divided into two groups, i.e., molecules having larger mobility are transported forward and those with smaller mobility backward. The threshold of this separation is determined by the timing of the ratcheting. Although separation resolution of the single cycle is deteriorated due to its short separation path (∿ 10 μm), it is sufficiently compensated by repeating the cycles. Thus, the REM provides very quick and accurate separation with a small occupied space and a low voltage. The authors have designed the first prototype of the REM as shown in Fig. A-1. Transport characteristics of DNA molecules have been analyzed by a computational simulation considering transient electric field determined by electrode voltages and concentration distribution of H^+ and OH^- ions in the aqueous solution. The results demonstrated that the chip has excellent separation capabilities. This prototype is now in the process of fabrication and experimental evaluation at UCB. On the other hand, some problems were found in the simulations; dispersion of analyte molecules is big when they leave the surface of the electrodes in the direction parallel to the surface, and small width of the microelectrodes that are needed to minimize the dispersion of molecules makes the chip susceptible to the Debye screening. To modify these problems, the crosswise migration type is considered as shown in Fig. A-2,where electrophoretic migration is driven as crossing the microchannel. Analyte molecules leave the surface of the electrodes in the normal direction, which minimizes the dispersion of them, and maximized area of the electrodes makes the chip tough against the Debye screening. The computational simulation has been performed for this type of chip and satisfactory results were obtained.[figure]
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TED-AJ03-406 TRANSPORT OF BIOMOLECULES IN THE RATCHETING ELECTROPHORESIS MICROCHIP (REM)

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