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Materials

Liquid Crystals Extend Electrophoresis

Employing a liquid crystalline fluid phase opens up electrophoresis to separating symmetrical or uncharged particles

by Celia Henry Arnaud
October 25, 2010 | A version of this story appeared in Volume 88, Issue 43

MOLECULAR RACING
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Credit: Oleg Lavrentovich
Borosilicate spheres, imaged using crossed polarizers with a polarized microscope, move around a circular track. The inset shows the detail of two particles moving in opposite directions around the track.
Credit: Oleg Lavrentovich
Borosilicate spheres, imaged using crossed polarizers with a polarized microscope, move around a circular track. The inset shows the detail of two particles moving in opposite directions around the track.

Employing a liquid-crystalline fluid phase, researchers at Kent State University’s Liquid Crystal Institute have extended the capability of electrophoresis to include separating symmetrical or uncharged particles (Nature 2010, 467, 947). Electrophoresis is usually performed in an isotropic fluid such as water with direct current, conditions under which separations are typically limited to charged or highly asymmetric species. Oleg D. Lavrentovich, Israel Lazo, and Oleg P. Pishnyak instead used a nematic liquid crystal as the fluid for electrophoresis of spherical dielectric and metal particles. In the nematic phase, the particle velocity is quadratically related to the applied voltage instead of linearly related, as is usually the case. Electrophoresis was therefore possible with an alternating current, which induced the particles to move as a result of asymmetry of the fluid phase rather than as a result of the charge or asymmetry of the particles themselves. These findings open up electrophoresis to particles of any charge or shape, the researchers note. “The phenomenon offers new perspectives for practical applications where highly flexible, precise, and simple control of particle (or cargo) placement, delivery, mixing, or sorting is needed,” they write.

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