dielectrophoretic

Dielectrophoretic refers to the forces and phenomena that arise when dielectric particles are subjected to non-uniform electric fields, most commonly in the context of dielectrophoresis (DEP). DEP describes the motion of neutral, polarizable particles caused by induced polarization in field gradients, allowing manipulation without the need for direct charge on the particles.

In DEP, movement results from the interaction between the induced dipole in the particle and the non-uniform electric field. The force depends on the particle size, the medium’s permittivity, the frequency-dependent complex permittivities of the particle and surrounding medium, and the gradient of the squared electric field. A common expression for the DEP force is F_DEP = 2π ε_m r^3 Re[f_CM] ∇(E_rms^2), where ε_m is the medium permittivity, r is the particle radius, E_rms is the root-mean-square field, and Re[f_CM] is the real part of the Clausius–Mossotti factor.

DEP can be positive (pDEP), with particles moving toward regions of higher field strength when Re[f_CM] > 0, or negative (nDEP), with particles moving toward regions of lower field strength when Re[f_CM] < 0. The sign and magnitude of DEP depend on frequency, due to the frequency dependence of the complex permittivities. This enables selective manipulation of different cell types or particles by tuning the applied frequency and field geometry.

Applications are widespread in microfluidics and lab-on-a-chip systems, including cell sorting, trapping, concentrating, and label-free characterization of biological cells and colloids. Practical use requires careful control of medium conductivity, temperature, and electrode design to minimize heating and electrothermal effects. The concept has historical roots in mid-20th century studies and has become a staple technique in biomedical and materials research.