Andreas Voigt

Single micro electrode dielectrophoretic tweezers for manipulation of suspended cells and particles.

Cells or particles in aqueous suspension close to a single capacitively coupled micro electrode (CCME) driven with high frequency electric fields experience dielectrophoretic forces. The effects near the CCME can be used for trapping and manipulation of single cells using externally metallised glass pipettes and might be used to develop a microscope based on force or capacitance measurements in conductive media.

Charge distribution within cell surface coats of single and interacting surfaces—a minimum free electrostatic energy approach. Conclusions for electrophoretic mobility measurements

The fixed charge distribution in a cell surface coat model was calculated using a variational approach based on the minimum of electrostatic free energy. The influence of ionic strength on distribution was analyzed. It is shown that interaction with other coats or smooth surfaces changes the fixed charge distribution. The special effect of a possible membrane charge was calculated in addition. In this case there is a fixed, charge-free space near the membrane, depending on coat thickness, ionic strength and membrane charge/surface coat charge ratio. For several cases energies, electric potentials and fixed charge distributions are given. The general result is that fixed charge distribution is always composed of a constant space charge density over a part of or the whole surface coat and, with some exceptions, of a surface charge density at the border of the surface coat. Conclusions for electrophoretic mobility measurement interpretations are drawn.

Free energy of the electrostatic interaction of cells with adjacent charged glycoprotein layer: A theoretical approach

Abstract The distance-dependent free energy of the electrostatic interaction is calculated for thick dielectric membranes of low dielectric constant in electrolyte solutions with adjacent charge-carrying glycoprotein layer (glycocalix). The charges are assumed to be continuously distributed. For the description of the space dependence of the charge density on the space coordinate perpendicular to the membrane surfaces various functions are used. The free energy corresponding to the space charge arrangement is determined by a stepwise charging process where the mobile ions are in thermodynamic equilibrium. For various charge arrangements of the interacting glycocalices the electric potential profile between the cells and the electrostatic contribution to the free energy are calculated. The model can be applied within the range of validity of the linearized Poisson-Boltzmann equation.

Electric-field-mediated inhibition of cell and microparticle adhesion: a new way to create bio-repellent surfaces

Abstract Ultramicroelectrodes fabricated by electron-beam lithography (width and height between 200 nm and 1 μm) are used for active alteration of the adherence properties of surfaces. We show that a.c. electric fields of low amplitudes (≈ 1 V) and high frequencies (> 1 MHz) can repel living cells and suspended microparticles. To reduce heat production and improved biorepellance, the electrodes are embedded in or insulated by thin dielectric layers (several hundred nanometres). These devices can possibly be used to keep sensor surfaces clean and they are an alternative way of producing bio-repellant surfaces.

Characterisation of cell movement by impedance measurement on fibroblasts grown on perforated Si-membranes

Mouse fibroblasts grown on perforated Si-membranes (pore diameter approximately 10 microns have been studied to clarify cell locomotive ability. The cell motility was microscopically monitored by a time-lapse video system and, simultaneously, the impedance of the growing cells was measured every 5 s. The correlations between observed cell activities and measured impedance events are discussed and classified. The method is sensitive and allows discrimination between signals arising from translocation of single cells and those arising from filopodia activities. Both cell and filopodia motion could be detected. Designs of microdevices fabricated in semiconductor technology are presented.