Dielectrophoresis (DEP) is a well-known technique for particle manipulation that has enabled a number of applications such as sorting, patterning, and filtering of many different cells, particles and molecules. The technique exploits the interaction between an electrical dipole induced on polarizable particles and an electric field gradient. Particles can be made to move towards a gradient maxima (positiveDEP) or minima (negativeDEP) depending on the polarizability differences between the targeted particle and the suspending media. Furthermore, a given particle suspended in a given media can display both DEP behaviors as the frequency of the field changes. This is illustrated in the videos below where a population of M. smegmatis cells (shiny dots) can either be attracted to the carbon electrodes (dark circles) as in positiveDEP, or repelled from them as in negativeDEP. Note that the sample is exactly the same and only the frequency of the applied field changes.
Positive DEP (note how cells are attracted to the carbon electrodes)
Negative DEP (note how cells are repelled from carbon electrodes)
Videos courtesy of Prof. Meltem Elitas when using carbon electrodes to induce a specific movement on M. smegmatis cells. PositiveDEP @ 7 MHz, NegativeDEP @ 100 kHz. From Lab Chip, 2014, 14, 1850-1857
The use of different materials or combination of them, including electrodes, electrical insulators, conductive liquids and composites, and fabrication approaches have led to the emergence of a number of techniques to implement DEP such as metal-electrode DEP, carbon-electrode DEP, insulator-based DEP and contactless DEP. In the M2L, we use carbon and titanium micro electrodes to implement DEP as well as light to illuminate a photosensitive material and enable the field gradients necessary for DEP in a technique known as light-induced DEP or optoelectronic tweezers
R. Martinez-Duarte, “Microfabrication Technologies in Dielectrophoresis Applications – a review”, Electrophoresis, 33, 3110-3132 (2012). Accepted Manuscript
J. Gilmore, M. Islam, J. Duncan, R. Natu and R. Martinez-Duarte, “Assessing the importance of the root mean square (RMS) value of different waveforms to determine the strength of a dielectrophoresis trapping force” Electrophoresis, 38, 2561-2564 (2017). Accepted Manuscript