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<sub>xo1</sub>, where cells in a non-uniform electric field undergo a transition from negative to positive DEP. Determination of f<sub>xo1</sub> 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<sub>xo2</sub> that occurs at much higher frequencies. Theory indicates that f<sub>xo2</sub> 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. <p><a href="http://dx.doi.org/10.5617/jeb.196" target="_blank">doi:10.5617/jeb.196 </a><br />J Electr Bioimp, vol. 2, pp. 64-71, 2011</p>
Dielectrophoresis (DEP) has been widely studied for its potential as a biomarker-free method of sorting and characterizing cells based upon their dielectric properties. Most studies have employed voltage signals from ∼1 kHz to no higher than ∼30 MHz. Within this range a transition from negative to positive DEP can be observed at the cross-over frequency f . The value of f is determined by the conductivity of the suspending medium, as well as the size and shape of the cell and the dielectric properties (capacitance, conductivity) of its plasma membrane. In this work DEP measurements were performed up to 400 MHz, where the transition from positive to negative DEP can be observed at a higher cross-over frequency f . SP2/O murine myeloma cells were suspended in buffer media of different osmolarities and measurements taken of cell volume, f and f . Potassium-binding benzofuran isophthalate (PBFI), a potassium-sensitive fluorophore, and flow cytometry was employed to monitor relative changes in intracellular potassium concentration. In agreement with theory, it was found that f is independent of the cell parameters that control f and is predominantly determined by intracellular conductivity. In particular, the value of f is highly correlated to that of the intracellular potassium concentration.
Electrical test structures have been designed to enable the characterisation of interdigitated electrode structures in conductive solutions, as used in dielectrophoresis. Test masks have been fabricated to explore the impact of array size, finger separation and solution conductivity on the applied electric field. A circuit model based on a distributed RC network is proposed and evaluated, demonstrating close agreement with actual impedance measurements. This provides the capability to readily predict the voltage and phase along the length of electrodes used for dielectrophoresis and other applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.