Figure 1.
Single shell model of a mamalian cell with dielectric parameters annoted.
Figure 2.
Plots of critical parameters and streamlines induced by AC electrokinetic forces.
(a.1) Plot of the real part of the Clausius-Mossotti factor for human cells with single shell models (parameters extracted respectively from [27] for HeLa-60) and σm = 2.10−2 S/m, (b.1) Plot of the ACEO mean velocities of the fluid near the electrodes (x = 1 µm) for several conductivities of the fluidic medium for water (εf = 78) and (c.1) Plot of the Π factor as a function of frequency for several conductivities of the medium. Review of predominant forces in presence of AC electric field and the induced motion of liquid and cells: (a.2) Dielectrophoresis (DEP) induces attraction (p-DEP) or repelling (n-DEP) of cells from high field region (in co-planar cases, electrode edges), (b.2) AC electroosmosis (ACEO) are electrohydrodynamic forces that create convective rolls over the electrodes edges and drag cell with them and (c.2) electrothermal effects (ETE).
Figure 3.
Summary of cells behaviors at (a) σm = 2.10−4 S/m and (b) σm = 2.10−2 S/m.
Photographs and schemes illustrate the cell motion for typical frequencies and magnitudes with corresponding graphs of the DEP (UDEP, green line) and EHD (UEHD, in red) velocities. The velocities were calculated according to the theoretical model presented in the first paragraph and position of the field was taken for x = 1 µm. The boxed text refers to the related paragraph.
Figure 4.
Time-lapse sequence images of cell destruction in conditions of dominant ACEO and ETE (f = 1 kHz, Vpp = 8 V, σm = 2 10−4 S/m) (a) picture of HEK cells taken in a microfluidi chip and (b) schema of the observed motions.
Cells are dragged in bulk rolls and the membrane rapidly breaks.
Figure 5.
Response of HEK cells to dielectrophoresis for increasing medium conductivities.
nDEP and pDEP are applied at f = 1 kHz and f = 200 kHz, respectively. The arrow represents cell motion during 5 frames (300 ms), the picture being the last image. DEP is stronger at low conductivities compared to EHD forces so cells experience larger displacement at higher velocities at low conductivities.
Figure 6.
Rotation study of three human cell lines.
(a1) Time-lapse sequence images of the rotation of HEK cells in the z-axis, in presence of 1 µm polystyrene colloid (highlighted in blue circles). Particles were added to observe medium stream lines. The red circle pinpoints a visible organelle. Rotation is studied at σm = 2.10−2 S/m when varying (a2) magnitude of the electric field at f = 45 kHz or (a3) frequency at magnitude 0.065 V/µm (V = 10 Vp-p). The dashed line plots the values of |Re[CMF(ω)]| at the same frequencies, bringing out the relation between DEP effect and ETE. Rotation studies of (b) of JURKAT cells and (c) PC3 cells (electric field magnitude is 0.089 V/µm (V = 4Vp-p) and σm = 2 10−2 S/m.). The inset on the lower part of the graphs shows the number of cells used for each mean value.
Table 1.
Table of the dielectric parameters for three human cell lines.