The Electrorotation as a Tool to Monitor the Dielectric Properties of Spheroid During the Permeabilization.

This paper proposes to monitor the spheroid's permeabilization within a dedicated microfluidic device using electrorotation analyses. The combination of two electric solicitations, the negative dielectrophoresis force (nDEP) for the spheroid trapping and the electrorotation torque for its dielectric characterization, is used. An estimation of the spheroid dielectric parameters is obtained through the analysis of the rotational velocity curve versus the electric field frequency before and after the PEF application. An observation set-up includes a fast camera that allows time controlled image sequence acquisition. Frames are then digitalized and from the analysis of the rotational velocity of the spheroid, its complex permittivity is determined. Different models, involving the variation of the dielectric properties of the concentric shells that constitute the spheroid, as well as the heterogeneity of cells within each shell, are proposed and used to determine its dielectric properties.

A microfluidic device with removable packaging for the real time visualisation of intracellular effects of nanosecond electrical pulses on adherent cells.

The biological mechanisms induced by the application of nanosecond pulsed electric fields (nsPEFs: high electrical field amplitude during very short duration) on cells remain partly misunderstood. In this context, there is an increasing need for tools that allow the delivering of such pulses with the possibility to monitor their effects in real-time. Thanks to miniaturization and technology capabilities, microtechnologies offer great potential to address this issue. We report here the design and fabrication of a microfluidic device optimized for the delivery of ultra short (10 ns) and intense (up to 280 kV cm(-1)) electrical pulses on adherent cells, and the real time monitoring of their intracellular effects. Ultra short electric field pulses (nsPEFs or nanopulses) affect both the cell membrane and the intracellular organelles of the cells. In particular, intracellular release of calcium from the endoplasmic reticulum was detected in real time using the device, after exposure of adherent cells to these nsPEFs. The high intensity and spatial homogeneity of the electric field could be achieved in the device thanks to the miniaturization and the use of thick (25 µm) electroplated electrodes, disposed on a quartz substrate whose transparency allowed real time monitoring of the nsPEFs effects. The proposed biochip is compatible with cell culture glass slides that can be placed on the chip after separate culture of several days prior to exposure. This device allows the easy exposure of almost any kind of attached cells and the monitoring in real time while exposed to nsPEFs, opening large possibilities for potential use of the developed biochips.

Selecting an electrode structure for cell sorting by differential dielectric affinity.

This paper focuses on the application of dielectrophoresis to on-chip cell sorting. Differential dielectric affinity separation is a "binary" technique, dividing a cell mixture into two distinct sub-populations. The principle and efficiency of this method are illustrated by potential energy plots of cells exposed to negative and positive dielectrophoresis. This paper aims at comparing several microelectrode structures, either bipolar or quadrupolar, in order to guide the choice of a geometry facilitating the sorting operation. This comparison relies on a 3D finite-elements calculation of the potential energy profiles obtained for each electrode shape.