DNA Migration and Separation on Surfaces with a Microscale Dielectrophoretic Trap Array

We studied the surface migration of DNA chains driven by a dc electric field across localized dielectrophoretic traps. By adjusting the length scale of the trap array, separation of a selected band of DNA was accomplished with a scaling exponent between mobility and number of base pairs similar to that obtained in capillary electrophoresis. We then provided a model, which predicts the trapping and extension of DNA chains at a dielectrophoretic trap responsible for the surface mobility and separation.

Figure 1

Electric field strength distribution and flow of field lines on the Au striped Si surface calculated by finite element method. Inset is the confocal image of $\lambda$ DNA migration across the surface under an electric field of $5\mathrm{V}/\mathrm{cm}$ showing the asymmetric accumulation of DNA at the $\mathrm{Au}/\mathrm{Si}$ interfaces. Scale bar is $30\mu \mathrm{m}$.

Figure 2

Calculated electric field $E$ and product of $E$ with its gradient, $EdE/dx$ along a line normal (a) and parallel (b) to the substrate through an $\mathrm{Au}/\mathrm{Si}$ interface.

Figure 3

Snapshots of a $\lambda$ DNA chain migrating across an Au striped surface under an electric field of $5\mathrm{V}/\mathrm{cm}$. Images (a), (b) were taken when the stretching was maximum. The scale bar is $6\mu \mathrm{m}$.

Figure 4

Mobility of $\lambda$ DNA on Au striped patterns fitted with Eq. (1) (solid line). The stretched length over pattern spacing, $\beta$, was calculated using Eq. (2) (dashed line). Insets (a)–(c) are the CCD images of $\lambda$ DNA migration on surfaces with pattern spacing of 80, 12, and $3\mu \mathrm{m}$, respectively. Inset (d) is the illustration of one DNA chain tethered and stretched at an $\mathrm{Au}/\mathrm{Si}$ interface. Yellow, gray, and green areas indicate Au strip, Si substrate, and the trapping domain, respectively.

Figure 5

Log-log plot of mobilities for $\lambda$ DNA monocut mix (1.5 kbp–48.5 kbp) and T5 DNA (120 kbp) as a function of the number of base pairs, along with a plot of relevant $\beta$ values (dashed line) on an Au striped surface with pattern spacing of $3\mu \mathrm{m}$. The mobility data were fitted with 3 linear solid lines. Inset (a) is an electrophereogram showing separation of a $\lambda$ monocut mix. Inset (b) shows that both single and double trapping simultaneously occurred for $\lambda$ DNA migrating on $8\mu \mathrm{m}$ spacing pattern.