Single Cell Electrical Characterization Techniques
Résumé
In this chapter the possibility to electrically characterize the electroporation of single cells is discussed. During the electroporation process, the application of pulsed electric field (Transmembrane Voltage Induced by Applied Electric Fields) leads to the partial permeabilization of the cell membrane, opening access to the cytoplasmic compartment for drug delivery, for instance. The electric impedance of the cell is modified by such a treatment. Impedance measurement can thus be employed to characterize the permeabilization effect, on a given angular frequencies range, which leads to an impedance spectrum. The impedance spectrum measurement can be achieved even at the level of single cells. In that case, the distance between the detection microelectrodes and the cell must be considered in order to achieve a satisfactory sensitivity. In addition, when considering the impedance measurement of cells flowing through a microfluidic channel, fast detection is also required, as the cell is present between the measurement electrodes only for a short while. A specific strategy must then be employed to achieve such goal. In this case, instead of screening the whole frequencies spectrum, a few set of frequencies should be selected and mixed to be simultaneously injected prior to synchronous detection. Another way to assess the single cell impedance is the use of indirect methods based on the mechanical behavior of cells that polarize under the application of a stationary or propagative electrical field. In particular, electrorotation experiment provides the electrical characterization of the cell, which is dependent of its level of permeabilization, after the application of electrical field pulses. When such approach is used, the vicinity of electrodes is less critical as the main requirement lays on the homogeneity of the rotating electrical field. Finally, the possibility to focus the electroporation at the subcellular level is discussed in the chapter. Indeed, the use of micro- or nanotechnology permits to localize spatially the electroporation on a tiny portion of the membrane of single cells. Adherent cells can be locally electroporated, using nanosized electrodes, subsequently used to monitor the intracellular potential.