Pulsed electric field induced changes in dielectric properties of biological cells

Different electrical characteristics of cells not only determine their initial electrical responses to pulsed electric field exposure, but also allow devising exposure conditions for pulsed electric field treatments that can preferentially target specific cells, such as cancer cells. We have investigated the dielectric properties of Jurkat cells, a malignant human T-cell line, before and after application of microsecond and nanosecond pulsed electric fields by means of time domain reflectometry dielectric spectroscopy. Jurkat cells in suspension with a 10% volume fraction were exposed with a repetition rate of about 1 Hz to either 8 consecutive 1-kV/cm electroporation pulses of 100 μs, or 8 consecutive 18-kV/cm pulses of 300 ns. Electrode polarization has a significant effect on the low frequency measurements (<;1 MHz) and needs to be corrected. We modeled the effect with a constant-phase-angle element in series with the impedance of the cell suspension. A Cole-Cole relaxation function was employed to describe the dielectric dispersion of cell suspension. Preliminary data analysis shows that conductivities of cell suspensions increased dramatically following microsecond or nanosecond exposure, indicating that membrane poration had occurred. Further analysis based on combination of a Maxwell-Wagner mixture model and a single shell cell model suggests an increase in plasma membrane conductivity. The changes of low frequency conductivity of the cell suspensions were different for both regimens, indicating different membrane charging and pore forming mechanisms.