Separation of tumor cells with dielectrophoresis-based microfluidic chip

Abstract

The present work demonstrates the use of a dielectrophoretic lab-on-a-chip device in effectively separating different cancer cells of epithelial origin for application in circulating tumor cell (CTC) identification. This study uses dielectrophoresis (DEP) to distinguish and separate MCF-7 human breast cancer cells from HCT-116 colorectal cancer cells. The DEP responses for each cell type were measured against AC electrical frequency changes in solutions of varying conductivities. Increasing the conductivity of the suspension directly correlated with an increasing frequency value for the first cross-over (no DEP force) point in the DEP spectra. Differences in the cross-over frequency for each cell type were leveraged to determine a frequency at which the two types of cell could be separated through DEP forces. Under a particular medium conductivity, different types of cells could have different DEP behaviors in a very narrow AC frequency band, demonstrating a high specificity of DEP. Using a microfluidic DEP sorter with optically transparent electrodes, MCF-7 and HCT-116 cells were successfully separated from each other under a 3.2 MHz frequency in a 0.1X PBS solution. Further experiments were conducted to characterize the separation efficiency (enrichment factor) by changing experimental parameters (AC frequency, voltage, and flow rate). This work has shown the high specificity of the described DEP cell sorter for distinguishing cells with similar characteristics for potential diagnostic applications through CTC enrichment.

Figure 1

Schematic of the DEP cell sorter. One particle is represented as a free-body diagram with the hydrodynamic, DEP force, and resultant force vectors. Arrows indicate flow through the main channel (80% infusion rate) and through the side channel (20% infusion rate), respectively.

Figure 2

Schematic of experimental setup for conducting the separation of cell mixtures.

Figure 3

MCF-7 displacement due to negative DEP force, highlighted cells shown at differing times after AC current was applied to the two electrodes shown as the two dark areas. (a) Cells position right prior to application of current. (b) Cells moved away from electrode tips 2 s after the electrode activation. (c) Cells continuing negative DEP path at 4 s.

Figure 4

DEP spectra. (a) HCT116 DEP spectra for solutions of three different conductivities across the frequency range of 0.1 MHz to 100 MHz, and HCT-116 spectra with dyed (Hoechst 33342) samples at 0.1X PBS. In both cases (without and with dye), they have their first cross-over frequency at virtually the same value. (b) MCF-7 DEP spectra for solutions of three different conductivities across the frequency range of 0.1 MHz to 100 MHz. The dashed line intersects at 3.2 MHz, where the cell separation was most efficient.

Figure 5

Separation of MCF-7 (encircled) and HCT-116 (fluorescent). The circles are used to mark MCF-7. (a) Shows flow of HCT-116 and MCF-6 through the main channel prior to activation of the AC electric field. (b) Reflects flow through the channel after activation at 3.2 MHz where undyed cells (MCF-7) are aligned parallel to the electrode (dark region) and are being deflected into the side channel while the HCT-116 path is unaltered. (c) Shows a low specificity scenario of separation between the MCF-7 and HCT-116 with both being deflected into the side channel under a frequency of 2 MHz.

Figure 6

Relation between the enrichment factor and frequency for MCF-7 and HCT-116. At 3.2 MHz, the enrichment factor for MCF-7 and HCT116 is 93% and 28%, respectively. The relationship confirms the high specificity and optimum frequency of 3.2 MHz for the cell separation.

Figure 7

Relationship between the enrichment factor and voltage for MCF-7 under different flow rates. Voltage and flow rate were modified to optimize the process and to show how the efficiency of the system was impacted by changing these parameters.