**1. Introduction**

When a certain strong electrical pulse applied across a cell or tissue, the structures of the cell or tissue would be rearranged to cause the permeabilization of the cell membrane, named in early 1980's "electroporation"[1]. The theoretical and experimental studies of electric field effects on living cells with their bilayer lipid membrane has been studies in 1960's to 1970's century [1-6]. During these years, the researches were primarily dealt with reversible and irreversible membrane breakdown in vitro. Based on these research, the first gene transfer by custom-built electroporation chamber on murine cells was performed by Neumann et al. in 1982 [7]. When electric field (E≈0.2V, Usually 0.5-1V) applied across the cell membrane, a significant amount of electrical conductivity can increase on the cell plasma membrane. As a result, this electric field can create primary membrane "nanopores" with minimum 1 nm radius, which can transport small amount of ions such as Na+ and Cl through this mem‐ brane "nanopores". The essential features of electroporation included (a) short electric pulse application (b) lipid bilayer charging (c) structural rearrangements within the cell mem‐ brane (d) water-filled membrane structures, which can perforate the membrane ("aqueous pathways" or pores) and (e) increment of molecular and ionic transportation [8]. In conven‐ tional electroporation (Bulk electroporation) technique, an external high electric field pulses were applied to millions of cells in suspension together in-between two large electrodes. When this electric field was above the critical breakdown potential of the cell, a strong polarization of the cell membrane occur due to the high external electric field. Applying a very high electric field could be resulted in the formation of millions of pores into the cell membrane simultaneously without reversibility [9]. Several methods other than electropora‐ tion can be used for gene transfer like microprecipitates, microinjection, sonoporation,

© 2013 Santra et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 Santra et al.; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

endocytosis, liposomes, and biological vectors [10-16]. But electroporation have some advantages when compared to other gene transfer methods such as, (a) easy and rapid operation with high reproducibility due to control of electrical parameters (b) higher transformation efficiency when compared to CaCl2 and PEG mediated chemical transforma‐ tion (c) controllable pore size with variation of electrical pulse and minimizing effect of cytosolic components, and (d) easy to uptake DNA into cells with smaller amount, when compared to other techniques [17-19]. For bulk electroporation, drug delivery can be performed in homogeneous electric field, whereas as single cell electroporation (SCEP), can introduce an inhomogeneous electric field focused on targeted single adherent or suspend‐ ed cell without affecting other neighboring cells. Both techniques can deliver molecules such as DNA, RNA, anticancer drugs into cells in–vitro and in-vivo. However SCEP is more advanced technique compared to the bulk electroporation technique. Recently researchers are concentrating on more advanced research area, such as localized single cell membrane electroporation (LSCMEP), which is an efficient and fast method to deliver drugs into single cell by selective and localized way from millions of cells. This LSCMEP can judge cell to cell variation precisely with their organelles and intracellular biochemical effect. This process can deliver more controllable drug delivery inside the single cell with application of different pulse duration. Both single cell electroporation (SCEP) and localized single cell membrane electroporation (LSCMEP) can provide high cell viability rate, high transfection efficiency, lower sample contamination, and smaller Joule heating effect in comparison with bulk electroporation (BEP) process.
