Validation of Clausius–Mossotti Function in Wideband Single-Cell Dielectrophoresis

For the first time, both lower and upper crossover frequencies of the real part of the Clausius-Mossotti function were calculated by using cell parameters measured on the same ultrawideband setup as that for single-cell dielectrophoresis. The calculation suggests that the lower crossover frequency can be from 0 to 127 kHz and that the upper crossover frequency can be from 45 to 108 MHz, in the unlikely case when uncertainties in the cell parameters all add up. The calculated lower crossover frequency was found to be in general agreement with the measured values of 28 ± 4 kHz. However, the calculated upper crossover frequency was significantly different from the measured values of 326 ± 35 MHz. The difference can be attributed to the field being highly nonuniform in single-cell dielectrophoresis, especially at higher frequencies. Additionally, with closely spaced electrodes in single-cell dielectrophoresis, adhesive force may have to be considered, even for a relatively nonadherent Jurkat cell. In any case, the difference between the calculated and measured crossover frequency suggests that the classical Clausius-Mossotti function, originally derived from the Maxwell-Wagner mixture model of a cell suspension, may not apply to single-cell dielectrophoresis in a straightforward manner, especially at high frequencies.