Making Single-cell Electroporation with Microelectrodes Predictable and Reproducible.

Electroporation is the creation of transient pores in a membrane by the application of an external electric field. When using microelectrodes, which can be used to electroporate single-cells, for applying an electric field to the cell, there is a question of how much voltage to apply. Unlike in bulk electroporation where hundreds of volts may be applied between electrodes, a rather small voltage is applied to a microelectrode in single-cell electroporation. In the single-cell experiment with microelectrodes, a substantial fraction of the voltage does not exist in solution because it is lost at the microelectrode/solution interface. This problem is the same as the classical electrochemist's problem of knowing the 'iR' drop in solution and correcting for it to obtain true interfacial potential differences. Therefore, we have used current interruption experiments to determine the iR drop in solution near microelectrodes. Because the electric field produced by microelectrodes is inhomogeneous, computer simulations were preformed to understand the electric field distribution. Results of the current interruption are validated by comparing two independent measurements of the resistance in solution: one value results from the measured iR drop in conjunction with the known applied current. The other value results from a measured solution conductivity and a computer simulated cell constant. This paper shows how to calculate the approximate current required to electroporate a cell with a microelectrode of a particular size, shape and distance from the cell. Carbon fiber microelectrodes were used to electroporate single A549 cells using the current calculated