Dielectric properties of biological samples change with frequency of the interrogating electric field therefore can be used to obtain information about structures and various kinetic as well as bio-physical and –chemical processes in the cells. Direct trapping of cells on electrodes can be done by dielectrophoresis (DEP) where cells can be then analyzed using impedance measurements. Frequency dependence measurements suffer from polarization effect at the electrode/electrolyte interface, which is very significant at low frequencies. Capacitance measurements of S. Pombe cells at nanogap capacitors were taken and the obtained results show beta-dispersion, with relaxation at around 100 kHz, due charging of the outer cell membrane according to the Maxwell-Wagner effect. The frequency dependence of the permittivity in response to a step function of the type 1-exp(-t/T) can be given by the Debye equation. Trapped cells were tested in CV and GV measurements. The curves for untrapped and YPD media show a different frequency dependence as compared to the trapped curves. Frequency dependence (1 kHz to 100MHz) of capacitance and conductance was simulated using Comsol Multiphysics 3.4 using reported permittivity and conductivity of the cell interior and cell membrane.As obtained from measurements, relaxation occurs after 100 kHz, thus at lower frequencies, the field does not penetrate the cell membrane. At higher frequencies, the field penetrates the cell and due to the Maxwell-Wagner mechanism, charging of the membrane occurs causing the relaxation.
Journal: TechConnect Briefs
Volume: 1, Nanotechnology 2009: Fabrication, Particles, Characterization, MEMS, Electronics and Photonics
Published: May 3, 2009
Pages: 460 - 463
Industry sector: Sensors, MEMS, Electronics
Topics: MEMS & NEMS Devices, Modeling & Applications