DIELECTROPHORETIC SEPARATION OF CANCER-CELLS FROM BLOOD

Recent measurements have demonstrated that the dielectric properties o f cells depend on their type and physiological status. For example, MD A-231 human breast cancer cells were found to have a mean plasma membr ane 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) fo rce arises that depends on the particle dielectric properties. Therefo re, cells having different dielectric characteristics will experience differential DEP forces when subjected to such a field. In this articl e, we demonstrate the use of differential DEP forces for the separatio n 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 hydrodyn amic forces within a parabolic fluid flow profile. Electrorotation mea surements 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 the n predicted from the frequency and suspension conductivity dependencie s of cell DEP responses defined by these parameters. Cell separations were then undertaken for various ratios of cancerous to normal cells a t different concentrations. fluted cells were characterized in terms o f separation efficiency, cell viability, and separation speed, For exa mple, 100% efficiency was achieved for purging MDA-231 cells from bloo d at the tumor to normal cell ratio 1:1 x 10(5) or 1:3 x 10(5), cell v iability was not compromised, and separation rates were at least 10(3) cells/s. Theoretical and experimental criteria for the design and ope ration of such separators are presented.