Refinement of the theory for extracting cell dielectric properties from dielectrophoresis and electrorotation experiments

A modified theory is proposed for extracting cell dielectric properties from the peak frequency measurement of electrorotation (ER) and the crossover frequency measurement of dielectrophoresis (DEP). Current theory in the literature is based on the low frequency (DC) approximations for the equivalent cell permittivity and conductivity, which are valid when the measurements are performed in a medium with conductivity less than 1 mS/m. The present theory extracts the cell properties through optimizing an expression for the medium conductivity in terms of the peak ER, or DEP crossover, frequency according to its definition using full expressions of equivalent cell permittivity and conductivity. Various levels of approximation of the theory are proposed and discussed through a scaling analysis. The present theory can extract both membrane and interior properties from the low and the high peak ER, or DEP crossover, frequencies for any medium conductivity provided the peak ER, or DEP crossover, frequency exists. It can be reduced to the linear theory for the low peak ER and DEP crossover frequencies in the literature when the medium conductivity is less than 10 mS/m. However, we can determine the membrane capacitance and conductance via the slope and intercept, respectively, of the straight line fitting of the ER peak and DEP frequency against medium conductivity data according to the linear theory only when the intercept dominates the experimental uncertainty, which occurs when the medium conductivity is less than 1 mS/m in practice. (C) 2011 American Institute of Physics. [doi:10.1063/1.3659282]