A new type of capacitance-coupled contactless conductivity detection (C(4)D) system with sidewall electrodes was proposed for integration on a silicon-on-isolator-poly(dimethylsiloxane) (SOI-PDMS) hybrid low-voltage-driven electrophoresis microchip. By a microelectromechanical system process, the sidewall electrodes were fabricated precisely at either side of the separation channel. The area of the capacitor electrodes was the maximum value to improve the detection sensitivity with an enhanced capacitance effect. According to the simulation results, the structural parameters of the sidewall electrodes were determined as 550-microm length, 15-microm width, 80-microm separation distance, and 1-microm isolator thickness. The integrated microdevice with the SOI-PDMS hybrid electrophoresis microchip was very compact and the size was only 15 cm x 15 cm x 10 cm (width x length x height), which permitted miniaturization and portability. The detector performance was evaluated by K(+) testing. The detection limit of the conductivity detector was determined to be 10(-9) and 10(-6) M for K(+) in the static and electric-driven modes, respectively. Finally, the C(4)D was applied to low-voltage-driven electrophoresis on a microchip to carry out real-time measurement of the separation of amino acids. The separations of 10(-4) M lysine and phenylalanine in the low-voltage-driven electrophoresis mode were performed with an electric field of 300 V/cm and were completed in less than 15 min with a resolution of 1.3. The separation efficiency was found to be 1.3 x 10(3) and 2.8 x 10(3) plates for lysine and phenylalanine, respectively, with a migration time reproducibility of 2.7 and 3.2%. The conductivity detection limit of amino acids achieved was 10(-6) M. The proposed method for the construction of a novel C(4)D integrated on an SOI-PDMS hybrid low-voltage-driven electrophoresis microchip showed the most extensive integration and miniaturization of a microdevice, which is a further crucial step toward the realization of the "lab-on-a-chip" concept.
In this paper, a new approach for the separation of amino acids on the electrophoresis chip-based low-voltage-driven electrophoresis was reported in detail. This low-voltage-driven electrophoresis process could be realized by powering directly the arrayed electrode pairs with low direct current (DC) voltage to generate a moving electric field along the separation microchannel, which could maintain enough electric field strength for electrophoresis. The proposed microfluidic electrophoresis chip was bonded directly with silicon-on-insulator (SOI) substrate and polydimethylsiloxane (PDMS) cover plate at room temperature. The microfluidic channels and the arrayed electrodes were etched on SOI wafer by silicon microelectromechanical system technology. A specially integrated circuit was proposed to power a 30-60-V DC voltage to particular sets of these electrode pairs in a controlled sequence such that the moving electric field could be formed, and the low-voltage-driven electrophoresis could be realized in the microchannel. In the experiments, with 10(-4) mol/L phenylalanine and lysine as analytes, the separation of amino acids on the low-voltage-driven electrophoresis microchip was conducted by homemade integrated control circuit; a method for separating amino acids was well established. It was also shown that the phenylalanine and lysine mixture was effectively separated in less than 7 min and with a resolution of 2.0. To the best of our knowledge, the low-voltage-driven microchip electrophoresis device could be of potential prospective in the fields of integrated and miniaturized biochemical analysis system.
This paper discusses the fabrication of Si-PDMS low voltage capillary electrophoresis chip (CE chip). Arrayed-electrode which is used to apply low separation voltage is fabricated along the sidewalls of the separation channel on the silicon based bottom part. Isolation trenches, which are placed surrounding the arrayed-electrode, insure the insulation between the arrayed-electrode, as well as arrayed-electrode and liquid in the micro channel. Polydimethylsilicone (PDMS) is used as the cover. PDMS and silicon based bottom part are reversible sealed to attain Si-PDMS low voltage CE chip. Experiments have been done to obtain optimum electrophoresis separation condition: separation voltage is 45V, switch time is 2s and the Phe and Lys electrophoresis separation is successful.
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