Dielectrophoresis

Dielectrophoresis assembles cancer cells in a three-dimensional microfluidic model.

In dielectrophoresis , an inhomogeneous electric field - consisting of direct current (DC) and alternating current (AC) - is used to manipulate particles. The inhomogeneous field induces a dipole moment in the particles , which then interacts with the applied field: the particles experience a force and - depending on the field and dipole moment - move in areas of higher (positive DEP) or lower (negative DEP) Field strength . The force effect is proportional to the volume of the particles. In this way, particles can also be captured in a "field cage" depending on their size. Dielectrophoresis is used for sorting and detecting nanoparticles , viruses, etc.

Dipole molecule moves in the inhomogeneous field in the direction of higher field strength

For a cylinder that is parallel to the field with a radius and half the length with a dielectric constant in a medium with a constant , the dielectrophoretic force is given by: ${\ displaystyle a}$ ${\ displaystyle b}$ ${\ displaystyle \ varepsilon _ {p}}$ ${\ displaystyle \ varepsilon _ {m}}$

{\ displaystyle F _ {\ mathrm {dep}} = {\ frac {\ pi a ^ {2} b} {3}} \ varepsilon _ {m} {\ textrm {Re}} \ left \ {{\ frac { \ varepsilon _ {p} ^ {*} - \ varepsilon _ {m} ^ {*}} {\ varepsilon _ {m} ^ {*}}} \ right \} \ nabla \ left | {\ vec {E} } \ right | ^ {2}}

One application in biology is e.g. B. to move a cell in an inhomogeneous alternating electric field regardless of its surface charge. For a polarizable sphere (e.g. a spherical cell) the following equation applies as a good approximation:

{\ displaystyle F _ {\ mathrm {dep}} = 2 \ pi a ^ {3} \ varepsilon _ {0} \ varepsilon _ {1} {\ frac {(\ varepsilon _ {2} - \ varepsilon _ {1} )} {(\ varepsilon _ {2} +2 \ varepsilon _ {1})}} \ nabla \ left | E \ right | ^ {2}}

{\ displaystyle \ nabla}

: Nabla - Operator (field inhomogeneity between two points)

{\ displaystyle \ varepsilon _ {0}}

: absolute dielectric constant (8.85 10 ⁻¹² F m ⁻¹ )

{\ displaystyle \ varepsilon _ {1}}

: relative dielectric constant of the medium

{\ displaystyle \ varepsilon _ {2}}

: relative dielectric constant of the cell

E : electric field strength

literature

Frieder Ostermaier: Curvature-sensitive biomembrane sensors: A structure with carbon nanotubes . Ed .: Frank OR Fischer. Springer-Verlag, Wiesbaden 2016, ISBN 978-3-658-11926-3 , p. 50–53 ( limited preview in Google Book Search).