Development of Lab-on-a-chip system for electroporation by electrophoresis of a charged droplet

Abstract

Many microfluidic devices especially droplet-based microfluidic system, have adopted electric force as an actuation method, because the actuation method using electric force is easily integrated with various microfluidic systems. The direct charging and subsequent electrophoretic control of a droplet in a dielectric liquid have been studied by a number of researchers as a novel droplet manipulation method. The electrophoresis of a charged droplet (ECD), which is one of the droplet control methods with electric force, has some advantages as a droplet actuation method; a simple and straightforward principle, minimum contact with solid surface, easy controllable coalescence, and fast moving velocity. ECD method can be used for the miniaturized chemical and biological reactor and assay due to the precise control of an individual droplet In this thesis, we developed microfluidic devices based on the ECD and demonstrated various chemical and biological experiments to prove their potential as novel droplet-based microfluidic platforms. We have made a digital microfluidic system based on a direct electric charging and subsequent electrophoretic manipulation of droplets by simple fabrication at low cost. Digitally controlled two-dimensional droplet motions are demonstrated by digital polarity control of an array of electrode. By independent control of droplets and colorimetric detection, the coalescence and mixing of droplets can be analyzed quantitatively. The gelation of sodium alginate and the crystallization of calcium carbonate by multiple droplet translations and coalescence and the actuation of glassy carbon beads are demonstrated to show the versatile manipulation capability of the ECD chip system. The implications and potentials of the ECD based microfluidic platform are also discussed. A unique digital microfluidic electroporation (EP) system has been demonstrated successfully and shows higher transgene expression than that of conventional techniques, in addition to reliable productivity and feasible integrated processes. By systematic investigations into the effects of the droplet EP conditions for a wild-type microalgae, 1 order of magnitude higher transgene expression is accomplished without cell wall removal than the conventional bulk EP system. In addition, the newly proposed droplet EP method by a droplet contact charging phenomena shows a great potential for the integration of EP processes and on-chip cell culture providing easy controllability of each process. The implications of the accomplishments and future directions for development of the proposed technology are discussed. Furthermore, the continuous droplet electroporation system has been investigated to accomplish higher productivity of the electroporation by modifying the droplet electroporation system based on ECD method with nozzle electrodes, which are used for continuous inlet and outlet of the cell solution. Optimal conditions for continuous EP including applied electric potential and flow rate are investigated by numerical simulations. In numerical studies, the electric field distribution and electric field strength exerted on cells in the continuous EP system are compared with those of the static EP system. Continuous droplet EP experiments are performed and intracellular DNA delivery is confirmed by the confocal microscopy. The parallel continuous droplet EP system is also developed by introducing additional electrode pairs into the EP system for the better productivity.