The application of dielectrophoresis to particle discrimination, separation, and fractionation is reviewed, some advantages and disadvantages of currently available approaches are considered, and some caveats are noted.

Electrorotation measurements were used to demonstrate that the dielectric properties of the metastatic human breast cancer cell line MDA231 were significantly different from those of erythrocytes and T lymphocytes. These dielectric differences were exploited to separate the cancer cells from normal blood cells by appropriately balancing the hydrodynamic and dielectrophoretic forces acting on the cells within a dielectric affinity column containing a microelectrode array. The operational criteria for successful particle separation in such a column are analyzed and our findings indicate that the dielectric affinity technique may prove useful in a wide variety of cell separation and characterization applications.Cell separation has numerous applications in medicine, biotechnology, and research and in environmental settings. For example, the use of autologous bone marrow transplants in the remediation of advanced cancers requires the removal of cancer cells from the patient's marrow (1), the study of signaling between blood cells requires purified cell subpopulations (2), and the purification of contaminated water supplies necessitates elimination of parasites such as Giardia and Cryptosporidium (3,4). Current sorting technologies usually exploit differences in cell density, immunologic targets, or receptor-ligand interactions. These techniques are often inadequate, producing insufficiently pure cell populations, being too slow, or being too limited in the spectrum of target cells. Identification of novel properties by which different cell types may be discerned and of new ways for their selective manipulation are clearly fundamental components for improving sorting methodologies.A particle suspended in a medium of different dielectric characteristics becomes electrically polarized when subjected to an alternating electrical field. Interaction between this induced polarization and the field gives rise to various electrokinetic effects. For example, a spatially inhomogeneous field will exert a lateral dielectrophoretic (DEP) force on the particle, directing it toward the minimum of dielectric potential (5-9), while a rotating field will induce particle electrorotation (ROT; refs. 10-12). The frequency dependencies of the magnitude and direction of these forces are functions of the intrinsic electrical properties of the particle that depend on the particle constitution and structural organization (13-15). For living cells, these characteristics are defined by composition, morphology, and phenotype (16, 17). Thus, DEP and ROT have been used to study bacteria (18), yeasts (11,19), plant cells (10), and mammalian cells (20,21) and to investigate cellular alterations accompanying physiological changes such as mitotic stimulation (16) and induced differentiation (7,17,21 MATERIALS AND METHODS Cells. Peripheral blood was collected by venipuncture into 90 parts Ca2+/Mg2+-free phosphate-buffered saline containing 5 mM hemisodium EDTA to prevent clotting. T lymphocytes were obtained from (human immunodeficiency virusa...

The application of dielectrophoretic field-flow fractionation (depFFF) to the isolation of circulating tumor cells (CTCs) from clinical blood specimens was studied using simulated cell mixtures of three different cultured tumor cell types with peripheral blood. The depFFF method can not only exploit intrinsic tumor cell properties so that labeling is unnecessary but can also deliver unmodified, viable tumor cells for culture and/or all types of molecular analysis. We investigated tumor cell recovery efficiency as a function of cell loading for a 25 mm wide × 300 mm long depFFF chamber. More than 90% of tumor cells were recovered for small samples but a larger chamber will be required if similarly high recovery efficiencies are to be realized for 10 mL blood specimens used for CTC analysis in clinics. We show that the factor limiting isolation efficiency is cell-cell dielectric interactions and that isolation protocols should be completed within ~15 minutes in order to avoid changes in cell dielectric properties associated with ion leakage.

Exosomes are a distinct source of tumor DNA that may be complementary to other liquid biopsy DNA sources. A higher percentage of patients with localized PDAC exhibited detectable KRAS mutations in exoDNA than previously reported for cfDNA. A substantial minority of healthy samples demonstrated mutant KRAS in circulation, dictating careful consideration and application of liquid biopsy findings, which may limit its utility as a broad cancer-screening method.

Recent measurements have demonstrated that the dielectric properties of cells depend on their type and physiological status. For example, MDA-231 human breast cancer cells were found to have a mean plasma membrane specific capacitance of 26 mF/m(2), more than double the value (11 mF/m(2)) observed for resting T-lymphocytes. When an inhomogeneous ac electric field is applied to a particle, a dielectrophoretic (DEP) force arises that depends on the particle dielectric properties. Therefore, cells having different dielectric characteristics will experience differential DEP forces when subjected to such a field. In this article, we demonstrate the use of differential DEP forces for the separation of several different cancerous cell types from blood in a dielectric affinity column. These separations were accomplished using thin, flat chambers having microelectrode arrays on the bottom wall. DEP forces generated by the application of ac fields to the electrodes were used to influence the rate of elution of cells from the chamber by hydrodynamic forces within a parabolic fluid flow profile. Electrorotation measurements were first made on the various cell types found within cell mixtures to be separated, and theoretical modeling was used to derive the cell dielectric parameters. Optimum separation conditions were then predicted from the frequency and suspension conductivity dependencies of cell DEP responses defined by these parameters. Cell separations were then undertaken for various ratios of cancerous to normal cells at different concentrations. Eluted cells were characterized in terms of separation efficiency, cell viability, and separation speed. For example, 100% efficiency was achieved for purging MDA-231 cells from blood at the tumor to normal cell ratio 1:1 x 10(5) or 1:3 x 10(5), cell viability was not compromised, and separation rates were at least 10(3) cells/s. Theoretical and experimental criteria for the design and operation of such separators are presented.