On-chip DNA preconcentration in different media conductivities by electrodeless dielectrophoresis

Abstract

Electrodeless dielectrophoresis is the best choice to achieve preconcentration of nanoparticles and biomolecules due to its simple, robust, and easy implementation. We designed a simple chip with microchannels and nano-slits in between and then studied the trapping of DNA in high conductive medium and low conductive medium, corresponding to positive and negative dielectrophoresis (DEP), respectively. It is very important to investigate the trapping in media with different conductivities since one always has to deal with the sample solutions with different conductivities. The trapping process was analyzed by the fluorescent intensity changes. The results showed that DNA could be trapped at the nano-slit in both high and low conductive media in a lower electric field strength (10 V/cm) compared to the existing methods. This is a significant improvement to suppress the Joule heating effect in DEP related experiments. Our work may give insight to researchers for DNA trapping by a simple and low cost device in the Lab-on-a-Chip system.

FIG. 1.

A schematic diagram showing the fabrication process for nanofluidic chip with two microchannels and a nano-slit in between. The inset at the lower right corner is the real picture of fabricated device which has four reservoirs for inlets and outlets.

FIG. 2.

Illustration of nanofluidic device for DNA trapping: (a) the optical image of channel layout consists of two microchannels and nano-slits in between. The inset is the enlarged picture for one unit; (b) the 3D image of nano-slit with the size of 1 μm. Picture is taken by AFM; (c) the 2D image of the slit and (d) the height profile of the red line in (c).

FIG. 3.

Comparison of electric field distribution near the junctions of different sizes: (a) channel size shrinks from 100 μm to 10 μm and (b) channel size shrinks from 100 μm to 1 μm. The strength of the electric field is indicated by color bar on the right of the figure. Electric field is most intense at the junction. The red arrows indicate the direction and magnitude of DEP force.

FIG. 4.

The trapping mechanism of DNA near the nano-slit: (a) the diffusion of DNA from one channel (A) to another (B) without applied electric field and (b) the trapping of DNA fragments after applying electric signal of 5 V for 1 min. The buffer solution used was 0.5× TBE buffer.

FIG. 5.

The electroosmotic effect between channels A and B when applied voltage was 5 V. The solution used in this experiment was rhodamine B in 500 mM NaCl and 0.5× TBE solution (channel A).

FIG. 6.

DNA trapping at the nano-slit when electric signal of 5 V (10 V/cm) was applied. (a)–(f) The fluorescent images captured at a time interval of 5 s and (a1)–(f1) is the change in fluorescent intensity after extracting the information from (a)–(f) by Matlab. The buffer solution used is 500 mM NaCl and 0.5× TBE. The X and Y axes is the pixel corresponding to the real picture and Z axis is the fluorescent intensity.

FIG. 7.

The electroosmotic effect observed when applied voltage was 5 V. The EO flow rate was 2.51 pl/s. The solution used in this experiment was rhodamine B dissolved in 0.5× TBE buffer solution (channel A).

FIG. 8.

DNA trapping at nano-slit when electric signal of 5 V (10 V/cm) was applied. (a)–(f) The fluorescent images captured at a time interval of 5 s and (a1)–(f1) is the change in fluorescent intensity after extracting the information from (a) to (f) by Matlab. The buffer solution used is 0.5× TBE. The X and Y axes is the pixel corresponding to the real picture and Z axis is the fluorescent intensity.