(441b) Dielectrophoretic Manipulation of Liver Cancer Cells

Lab on a chip devices are becoming increasingly important in many biomedical applications. Microfluidics offers important advantages that are critical in the biomedical field: fast response time, portability, low sample and reagent consumption.  One of the separation techniques with great potential to be used in microdevices dielectrophoresis (DEP). DEP has been successfully employed for the manipulation of biomolecules and cell.^1,2  DEP is the movement of particles due to polarization effects, when particles are exposed to a non-uniform electric field.³ There are two main approaches for the generation of non-uniform electric fields: employing arrays of microelectrodes or employing arrays of insulting structures. Most of the studies reported on DEP have been performed employing arrays of microelectrodes. However, electrode-based DEP has important drawbacks, since electrodes lose functionality due to fouling, which is a common effect when employing bioparticles. Additionally, fabrication of electrode-based systems is expensive and requires complex steps due to metal deposition processes.

Insulator-based DEP allows for more robust systems, since insulators can function despite of fouling, and can be fabricated from a variety of material, such as plastics, making it possible for inexpensive and disposable microdevices, ideal for biomedical applications.⁴

In this work, Hepatocellular carcinoma human cells (Hep-G2) were manipulated employing direct current electric fields and iDEP in a plastic microdevice. The device consisted of eight microchannels, each channel was 1-mm wide, 75-um deep, and 10.2-mm long. Every microchannel contained an array of cylindrical insulating posts that had a diameter of 150 um and were arranged 250 um center-to-center. A dove-tail geometry was added to first row of post in each side, in order to prevent cells from colliding against the posts and obstructing the system. The post array had 12 columns of 5 posts each, and was straddled by an inlet and outlet reservoirs. Electrodes were placed at the reservoirs in order to apply the electric field across the microchannel length (Figure 1).

Figure 1. Schematic representation of the experimental set-up, showing a sample of Hep-G2 cells at the inlet reservoir.

In order to allow visualization, Hep-G2 cells were dyed employing SYTO 9, a DNA-intercalating- fluorescent dye. In order to protect Hep-G2 cells from osmotic shock, cell were suspended in a dextrose solution at 5% which had a pH of 7.4 and a conductivity of 100 uS/cm.⁵

Figure 2 shows some of the results obtained. Figure 2a shows that Hep-G2 cells are immobilized by dielectrophoresis when a field of 150 V/cm was applied. The concentration of Hep-G2 cells increased by increasing the applied field, as shown in Figures 2b and 2c, where fields of 300 V/cm and 400 V/cm were applied, respectively.

Figure 2. Dielectrophoretic response of Hep-G2 cells, flow direction from left to right. Electric fields applied are: a) 150 V/cm, b) 300 V/cm, c) 400 V/cm. Cells were suspended in dextrose solution at 5% with a pH of 7.4 and a conductivity of 100  uS/cm.

From these results it can be seen that iDEP has the potential for the manipulation and concentration of Hep-G2 cells.  In the future, iDEP could be used in microdevices to identify and isolate cancer cells from a real sample, differentiating them from normal cells.  Opening the possibility for iDEP to be used as a tool for cancer diagnostics.

References

1.            Voldman, J, Electrical forces for microscale cell manipulation. Ann. Rev. Biomed. Eng. 2006;8:425.

2.            Lapizco-Encinas, BH, Rito-Palomares M, Dielectrophoresis for the manipulation of nanobioparticles. Electrophoresis. 2007;28(24):4521.

3.            Pohl, HA, The Motion and Precipitation of Suspensoids in Divergent Electric Fields. J. Appl. Phys. 1951;22(7):869.

4.            Simmons, BA, McGraw GJ, Davalos RV, Fiechtner GJ, Fintschenko Y, Cummings EB, The Development of Polymeric Devices as Dielectrophoretic Separators and Concentrators. MRS Bulletin. 2006;31:120. 

5              Polevaya, Y, Ermolina I, Schlesinger M, Ginzburg B-Z, Feldman Y, Time domain dielectric spectroscopy study of human cells II. Normal and malignant white blood cells. Biochimica et Biophysica Acta. 1999; 1419: 259.