Metastasis is the main cause of tumor-related death, and the dispersal of tumor cells through the circulatory system is a critical step in the metastatic process.

This paper presents an effective electrorotation technique for measuring the dielectric properties of cells using a superposed electrical signal, which can simultaneously generate negative quadrupolar dielectrophoretic (nQDEP) force and electrorotational (ROT) torque. The proposed technique involves a three-dimensional (3D) octode, which includes four electrodes arranged in a crisscross pattern on the top and bottom of a microchannel, respectively. A single cell was trapped in the center of the 3D octode by the nQDEP force and simultaneously rotated by the ROT torque. Using the proposed electrorotation technique, ROT spectra of human leukocyte subpopulations (T and B lymphocytes, granulocytes, and monocytes) and metastatic human breast (SkBr3) and lung (A549) cancer cell lines were accurately measured without any disturbance. Torque on the cells generated by the ROT signal was analyzed theoretically based on the single-shell dielectric model for the cells. Furthermore, the dielectric properties of the cells, such as area-specific membrane capacitance and cytoplasm conductivity, were extracted using the measured ROT spectra and the analyzed torque.

This paper presents lateral-driven continuous dielectrophoretic (DEP) microseparators for separating red and white blood cells suspended in highly conductive dilute whole blood. The continuous microseparators enable the separation of blood cells based on the lateral DEP force generated by a planar interdigitated electrode array placed at an angle to the direction of flow. The simplified line charge model that we developed for the theoretical analysis was verified by comparing it with simulated and measured results. Experimental results showed that the divergent type of microseparator can continuously separate out 87.0% of the red blood cells (RBCs) and 92.1% of the white blood cells (WBCs) from dilute whole blood within 5 min simply by using a 2 MHz, 3 Vp-p AC voltage to create a gradient electric field in a medium that conducts at 17 mS cm⁻¹. Under the same conditions, the convergent type of microseparator could separate out 93.6% of the RBCs and 76.9% of the WBCs. We have shown that our lateral-driven continuous DEP microseparator design is practical for the continuous separation of blood cells without the need to control the conductivity of the suspension medium, overcoming critical drawbacks of DEP microseparators.

We describe the lateral displacement of a particle passing over a planar interdigitated electrode array at an angle as a function of the particle size. The lateral displacement was also measured as a function of the angle between the electrode and the direction of flow. A simplified line charge model was used for numerically estimating the lateral displacement of fluorescent polystyrene (PS) beads with three different diameters. Using the lateral displacement as a function of particle size, we developed a lateral dielectrophoretic (DEP) microseparator, which enables continuous discrimination of particles by size. The microchannel was divided into three regions, each with an electrode array placed at a different angle with respect to the direction of flow. The experiment using an admixture of 3-, 5-, and 10-µm PS beads showed that the lateral DEP microseparator could continuously separate out 99.86% of the 3-µm beads, 98.82% of the 5-µm beads, and 99.69% of the 10-µm beads, simply by using a 200-kHz 12-Vp-p AC voltage to create the lateral DEP force. The lateral DEP microseparator is thus a practical device for simultaneously separating particles according to size from a heterogeneous admixture.