Dielectrophoresis (or DEP) is a phenomenon in which a force is exerted on a dielectric particle when it is subjected to a non-uniform electric field. This force does not require the particle to be charged. All particles exhibit dielectrophoretic activity in the presence of electric fields. However, the strength of the force depends strongly on the medium and particles' electrical properties, on the particles' shape and size, as well as on the frequency of the electric field. Consequently, fields of a particular frequency can selectively manipulate particles with great selectivity. This has allowed, for example, the separation of cells or the orientation and manipulation of nanoparticles.

For a field-aligned cylinder of radius $a$ and half-length $b$ with dielectric constant $\backslash epsilon\_p$ in a medium with constant $\backslash epsilon\_m$, the dielectrophoretic force is given by:

$F\_\{dep\}\; =\; \backslash frac\{\backslash pi\; a^2\; b\}\{3\}\backslash epsilon\_m\; \backslash textrm\{Re\}\backslash left\backslash \{\backslash frac\{\backslash epsilon^*\_p\; -\; \backslash epsilon^*\_m\}\{\backslash epsilon^*\_m\}\backslash right\backslash \}\backslash nabla\; \backslash left|\backslash vec\{E\}\backslash right|^2$

This is valid if the electric field does not change significantly over the particle length. The equation only takes into account the dipole formed and not higher order polarisation. Dielectrophoresis had been investigated a few decades ago (Pohl, 1978) but has recently been revived due to its potential in the manipulation of microparticles nanoparticles and cells. Phenomena associated with dielectrophoresis are electrorotation and traveling wave dielectrophoresis (TWDEP).

Dielektrophorese