Determination of Cell Dielectric Properties Using Dielectrophoretic Technique

Experiments were carried out on four cell types: Chlorella sp., Tetraselmis sp., and mesophyll protoplasts of Dendrobium and Lilium longiflorum. The speed of cell translation in between a pair of cylindrical electrodes was measured at different solution conductivities (σs). For each field frequency, the speed was plotted against the gradient of electric field squared to obtain the real part Re[f(ω)] of complex permittivity. Conductivity (σ) and permittivity (ε) of the cytoplasm and cell membrane were obtained by iterative method using a spherical single shell model. It was found that membrane permittivity (εm) of plankton cells was fairly large compared to that of mesophyll protoplasts, whereas the reverse was true for membrane conductivity (σm). The permittivity of cytoplasm (εc) varied from 105εo to 150εo for plankton and from 83εo to 105εo for the protoplasts. The estimated values for σc ranged from 8 to 40 mS.m for plankton and from 1 to 20 mS.m for the protoplasts. The cytoplasmic conductivity (σc) of the latter was the same as that of the external medium implying that these mesophyll protoplasts behave like lossy dielectric at σs between 1 mS.m to 20 mS.m. Possible specific membrane capacitance (Cm) varied from 6 to 12 mF.m for plankton and from 2 to 31 mF.m for the protoplasts.