(72a) Concentration and Separation of DNA Employing Insulator-Based Dielectrophoresis and DC Electric Fields

Insulator-based dielectrophoresis (iDEP) is an electrokinetic technique where particles move due to polarization effects when exposed to non-uniform electric fields, which can be induced either by direct current (DC) or alternating current (AC).¹  This novel technique has a great potential for miniaturization, and it has been successfully applied for the manipulation of a wide array of bioparticles, from biomolecules to microorganisms.^{2, 3}  The advantages of iDEP over the traditional electrode-based DEP are: inexpensive fabrication processes and the ability of employing electroosmotic flow to pump liquid when direct current (DC) electric fields are applied; making miniaturization more viable.^{4, 5}

In this work, iDEP is used to immobilize, concentrate, and separate DNA particles inside a microchannel with cylindrical insulating structures fabricated in glass. The microchannel is 10.16 mm-long, 2 mm-wide, and 7 um-deep; and the cylindrical posts are 470-um in diameter and are arranged 510-um center to center. Figure 1 is a schematic representation of the experimental set-up.

Figure 1. Experimental set-up showing the schematic representation of the microchannel employed, where DNA samples are placed at the inlet reservoir and an electrical field is applied between the two reservoirs.

Concentration of DNA particles was achieved when the applied DC field was increased to 1,500 V/cm, and a separation was obtained by applying a decreasing gradient of the field to release particles from the dielectrophoretic traps. DNA particles were visualized by employing a DNA intercalating dye. By employing the fluorescence detection it was possible to estimate concentration factors after trapping and release of the DNA particles. Figure 2 shows dielectrophoretic trapping of linear DNA (PET 28) by using a suspending medium with pH of 6 and a conductivity of 25 uS/cm.

Figure 2. Dielectrophoretic trapping of linear DNA (PET 28) under an electrical field of: a) 1,000 V/cm, b) 1,200 V/cm, and c) 1,500 V/cm, using a suspending medium with pH of 6 and conductivity of 25 uS/cm.

The results of this study can be used to further the development of a low cost, fast and efficient platform for the concentration and manipulation of DNA solutions for laboratory analysis and to aid in the preparation of pharmaceutical grade solutions for use in gene therapy studies.

References

1              M. P. Hughes Nanoelectromechanics in Engineering and Biology; CRC Press: Boca Raton, FL, 2002.

2              J. Voldman, Ann. Rev. Biomed. Eng., 2006, 8, 425-454.

3              B. H. Lapizco-Encinas, M. Rito-Palomares, Electrophoresis, 2007, 28, 4521-4538.

4              B. A. Simmons, G. J. McGraw, R. V. Davalos, G. J. Fiechtner, Y. Fintschenko, E. B. Cummings, MRS Bulletin, 2006, 31, 120-124.

5              E. B. Cummings, A. K. Singh, Anal. Chem., 2003, 75, 4724-4731.