Abstract
Isolation of cells and their transfection in a controlled manner is an integral step in cell biotechnology. Electric field approaches such as dielectrophoresis (DEP) offers a more viable method for targeted immobilization of cells without any labels. For transfection of cells to incorporate exogenous materials, electrical methods such as electroporation, are preferred over chemical and viral delivery methods since they minimally affect cell viability and can target many types. However prior approaches to both methods required multiple excitation sources, an AC source for DEP-based trapping and another DC source for electroporation. In this paper, we present a first of its kind flow through lab-on-chip platform using a single AC excitation source for combined trapping using negative dielectrophoresis (nDEP) and AC electroporation. Use of AC fields for electroporation eliminates the unwanted side effects of electrolysis or joule heating at electrodes compared to DC electroporation. Adjusting the flow rate and the electrical parameters of the incident AC field precisely controls the operation (trap, trap with electroporation and release). The platform has been validated through trapping and simultaneous transfection of HEK-293 embryonic kidney cells with a plasmid vector containing a fluorescent protein tag. Numerical scaling analysis is provided that indicates promise for individual cell trapping and electroporation using low voltage AC fields.
Highlights
Analysis of cells at the single-cell level has become increasingly important for drug discovery, cancer genomics and discovery of new pathways[1]
Transfection, the latter of the required functions, can be accomplished through a temporary and reversible poration of cell membrane known as electroporation, which occurs under exposure of the cell to a high electric field
Use of this half-ring structure allows for continuous application of the electric field to trap cells under constant flow while simultaneously creating a negative DEP (nDEP) force acting in the negative z direction, bringing cells to the trap location independent of gravity
Summary
Analysis of cells at the single-cell level has become increasingly important for drug discovery, cancer genomics and discovery of new pathways[1]. DEP is arguably the simplest available method for both cell separation and confinement in microfluidic devices, requiring only generation of an electric field. This phenomenon uses inhomogeneous electric fields to exert a translational force on dielectric particles, similar to the Lorentz force which acts on charged particles in homogenous fields. Numerous lab-on-chip (LOC) devices have demonstrated DEP as a viable method for cell capture and immobilization[8,11–16] For this purpose, negative DEP (nDEP) in particular has been shown to dramatically improve cell viability compared to techniques using positive DEP (pDEP)[17,18]. The frequency and magnitude of the electric field required to induce poration is determined by the membrane capacitance and conductivities of the medium and cell[21]
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