Dielectrophoretic Characterisation of Mammalian Cells above 100 MHz

Dielectrophoresis (DEP) is a label-free technique for the characterization and manipulation of biological particles - such as cells, bacteria and viruses. Many studies have focused on the DEP cross-over frequency f_xo1, where cells in a non-uniform electric field undergo a transition from negative to positive DEP. Determination of f_xo1 provides a value for the membrane capacitance from the cell diameter, the means to monitor changes in cell morphology and viability, and the information required when devising DEP cell separation protocols. In this paper we describe the first systematic measurements of the second DEP cross-over frequency f_xo2 that occurs at much higher frequencies. Theory indicates that f_xo2 is sensitive to the internal dielectric properties of a cell, and our experiments on murine myeloma cells reveal that these properties exhibit temporal changes that are sensitive to both the osmolality and temperature of the cell suspending medium.