Rapid Cell Separation Using 3D Carbon Electrode Dielectrophoresis

Rapid cell separation using 3D carbon electrode dielectrophoresis

Monsur Islam, Rucha Natu and Rodrigo Martinez-Duarte

Mechanical Engineering Department, Clemson University, Clemson, SC, USA

Here we present the initial results for rapid separation of two different particles from a particle mixture using carbon electrode dielectrophoresis (DEP). Isolation and concentration of pathogenic cells are one of the important steps in clinical diagnostic systems. Expensive and large laboratory equipment such as fluorescence activated cell sorting (FACS) are generally used for cell isolation; in a process that is relatively expensive and can take several hours. Here we propose a DEP-based microfluidic platform for rapid separation and concentration of cells. Preliminary results indicate separation of Candida albicans and latex beads of 10 µm diameter from the cell-particle mixture at a flow rate of 100 µl/min using streamingDEP.

C. albicans cells were grown in yeast malt broth (YMB, Sigma Aldrich, USA) culture for 2 days in a controlled environment at 37 °C. 150 µl of this cell culture was then inoculated in 4 ml of experimental buffer solution which contained 15% sucrose, 0.5% dextrose and 0.1% bovine serum albumin (BSA). The experimental cell suspension was prepared by washing and re-suspending the cells in the buffer solution. The concentration of the cell suspension was 7.18 x 10⁶ cells/ml. A particle suspension of 10 µm latex beads was also prepared in the buffer solution and concentration was measured 5.86 x 10⁶ particles/ml. A mixture solution was also prepared by mixing the cell suspension to the particle suspension in a 1:1 volume ratio.

The fabrication of the carbon electrode DEP device was reported elsewhere by our group [1]. DEP experiments were performed for both cell suspension, particle suspension and mixture solution. The carbon electrodes were stimulated with sinusoidal signal having magnitude of 20 Vpp and frequency of 250 kHz. At this conditions, C. albicans experience positive DEP and the 10 µm latex beads experience negative DEP. A constant flow rate of 100 µl/min was maintained throughout the experiments. At the cell density used in this work this would represent a throughput of ~10⁵ cells/min. The continuous separation principle shown here is based on attracting the targeted cell towards the electrode but not trapping it. Hence, an equilibrium between the positiveDEP and hydrodynamic drag force is sought. Streaming behaviour of C. albicans is illustrated in Figure 1a. Instead of streaming, latex beads experience focusing by negativeDEP and were focused in between the electrodes (Fig. 1b). When using the mixture solution, both the above mentioned phenomena occurred simultaneously and C. albicans and latex beads focused and flowed along different streamlines showing separation in Fig 1c. The results obtained when the electric field is off are shown in Fig. 1d, showing how the lines disappeared.

Ongoing work is to determine the maximum flow rate while still observing streaming behaviour. To this end, COMSOL is being used to determine the position of the streamlines at different flow rates. The fabrication of geometries that would allow for the continuous retrieval of the focused cells represents future efforts in this work.

References:

[1]      R. Martinez-Duarte, P. Renaud, and M. J. Madou, “A novel approach to dielectrophoresis using carbon electrodes.,” Electrophoresis, vol. 32, no. 17, pp. 2385–92, Sep. 2011.

Figure 1: Focusing of (a) C. albicans using positive DEP, (b) 10 µm latex beads using negative DEP; (c) Separation of C. albicans from 10 µm latex beads; (d) No focusing is observed when the field is turned off. The DEP parameters were 20 Vpp magnitude and 250 kHz frequency and the flow rate was 100 µl/min. Images taken at a rate of 100 fps.