Electrokinetic DNA concentration in microsystems

Active DNA concentration on a specific site in microsystems was demonstrated by the use of AC electroosmosis and electrophoresis. Two different sizes of DNA molecules, double-stranded λ-phage DNA (48.5 kbp) and single-stranded DNA in 20 nucleotides, were utilized in this study. In the DNA concentrator, AC electroosmosis induced by AC electric field could generate bulk fluid flow to transport DNA molecules from a large effective region to the electrode surface. Numerical simulation was done to show the motion of the bulk fluid flow. Electrophoresis induced by DC bias was applied simultaneously to hold the DNA molecules on the surface of the DNA concentrator. The applied electric field required only a low electric potential of a few volts. The motion of the DNA molecules under electrokinetic forces was observed under a fluorescence microscope. Experimental results showed the λ-phage DNA molecules could be concentrated by AC electroosmosis alone, and the single-stranded DNA molecules required the combined electrokinetic forces. The magnitude of AC electroosmotic flow and electrophoretic force controlled by the applied electric potential and frequency was also demonstrated through these concentration experiments.