Electromanipulation
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Electromanipulation is a micro-material analyzing method mostly used for manipulations of biological cells that uses properties of diverse electric fields. In nanotechnology, nanomaterials are so small that they can hardly be directly mechanically manipulated. Hence, electric fields are applied to them to make field-induced movements or deformations. It is a recently developed technology and is still in progress of widening applications. Types of Electronmanipulation includes dielectrophoresis, electro-rotation, electro-deformation, electro-disruption, electro-destruction, electroporation, and electro-fusion. Diverse electromanipulations are achieved using various electric fields including AC(alternating current), DC(direct current), and pulsed(deliver high-energy discharges at very short periods) electrical fields. Electromanipulation of cells permits diverse cell manipulations with minimal mechanical contact between cells and device structures. Although predominantly used in cells, electromanipulation also contributes to other scientific fields such as Hybridoma technology and nanoelectronic device development.
Dielectrophoresis (DEP)
There are seven types of electromanipulation, some are drastically different in purpose and function while some are closely related. The most developed and common type is dielectrophoresis. Various manipulations of micro-materials can be achieved using one or several of the seven electromanipulation. Distinct types sometimes require various electric fields or conditions.
Electric field applied: DC or AC oscillating (most cases)
Purpose: displacement
Condition: suspension media of low electrical conductivity; spatially non-uniform electric field[1]
Theory: DEP force is produced by differential polarizability of cells and their suspending medium. There are two types of DEP force, positive DEP (pDEP) and negative DEP (nDEP). pDEP points towards strong regions of the nonuniform electric field while nDEP points towards weak regions of the nonuniform electric field. Live cells can quickly be attracted to the electrode edge when applying DEP, thus separating live cells and dead cells. Dielectric properties of cells can be analyzed using measurements of DEP spectra of cells.[2]
Electro-rotation (ER)
Electric field applied: AC oscillating
Purpose: rotation
Condition: suspension media of low electrical conductivity; frequency is approximately the crossover frequency(DEP force is negligible)
Theory: ER changes the alignment of non-spherical cells by changing the frequency of the oscillating electric field.[2]
Electro-deformation (ED)
Electric field applied: AC oscillating
Purpose: deformation; compare viscoelastic and power-law properties of cells
Condition: suspension media of low electrical conductivity
Theory: ED controls and deforms cells that being attracted to the edge of the electrode edge(by DEP) by increasing AC potential[2]
Electro-disruption
Electric field applied: pulsed
Purpose: disruption of subcellular structures
Condition: non-uniform electric field
Theory: ED performs electromanipulation inside a cell which has compromised cytoskeletons and a detached nuclei. Deradated cells eject cytosolic contents and become "ghosts"(about 1.5 times the normal cell size). Ghosts can be deflected by pulsed fields and inflected by ac fields.[2]
Electro-destruction (lysis)
Electric field applied: pulsed
Purpose: lysis (the disintegration of a cell by rupture of the cell wall or membrane.)
Condition: non-uniform electric field
Theory: pDEP is used to increase the occurrence of lysis, and nDEP is used to decrease the occurrence of lysis. Conditions of cell lysis can be studied by switching pulsing amplitudes.[2]
Electro-poration (EP) and Electro-fusion (EF)
Electric field applied: pulsed
Purpose: Cell-membrane disruption
Condition: non-uniform electric field; dielectrophoretic alignment of cells
Theory: Cell membrane disruption can be achieved by switching amplitude, duration, pulses rate and number of pulses of the pulsed electric field. When cells' membranes are disrupted, some cells merge into one big cell which can be 3-4 times the size of a normal cell. There are two types of EP: One is irreversible EP which can lead to cytolysis(the bursting of cell membrane when excess water is in the cell); the other is reversible EP which helps maintain cells’ vitality while transforming molecules into cells.[2][1]
Development
In the early part of 20th century, discoveries of irreversible membrane breakdown and dielectrophoresis are made. Those discoveries serve as fundamental ideas of cellular electromanipulation. In late 20th century, cellular electromanipulation techniques was developed based on the discovery of later discovered reversible membrane breakdown.[3]