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Liquid Crystal Electrophoresis Technique Could Prove Useful for Protein Separations

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This story originally ran on Nov. 4.

By Adam Bonislawski

Researchers at Kent State University have devised an electrophoresis technique using liquid crystals that could prove useful as a separation method for biological material like proteins.

Detailed in a paper published the October edition of Nature, the technique uses alternating current, as opposed to the direct current required by conventional electrophoresis, and enables separation of particles based on both the electric field and the directionality of the liquid crystal molecules, Oleg Lavrentovich, director of Kent State's Liquid Crystal Institute and one of the paper's authors, told ProteoMonitor.

Because in conventional electrophoresis, particle velocity is linearly proportional to the electric field, only direct current can be used to drive and separate particles. According to Lavrentovich, however, the researchers demonstrated that when electrophoresis is done in liquid-crystalline nematic fluid, velocity is proportional to the square of the electric field, enabling the field to drive particles regardless of its polarity, allowing the use of alternating current.

This effect is rooted in the fact that the velocity of a particle in the liquid crystal media depends not only on the force of the electric field being applied, but also on the directionality of the liquid crystal molecules, Lavrentovich said. Particles are driven both by charge and by the asymmetric distortions of the liquid crystal orientations around them.

"The difference between the liquid crystal and regular [electrophoresis media] is that inside the liquid crystals, the molecules are parallel to each other, and that creates its own directionality," he said. "So, if I have not only the directionality of the electric field, [but also] some other directionality in the system, then the velocity of the particle will depend on both vectors – the vector of the electric field and the vector of the orientation of the molecules [that compose the medium]."

Using alternating current reduces undesirable electrochemical reactions caused by direct current and provides for easier generation of a constant, sustained electric field, Lavrentovich said. Being able to drive particles along multiple vectors, meanwhile, provides increased flexibility for sorting.

"Imagine you have two particles in liquid crystal. One is charged and another one is neutral. So the charged particle will experience two forces [from the electric field and the orientation of the liquid crystal molecules] – let's say west and north directed – and as a result it will move in the northwest direction and the uncharged particle will move in only the north direction," he said. "We have two vectors, two directionalities, to play with, and that, of course, gives higher flexibility."

Because the particles' movements depend on distortions to the directionality of the liquid crystals surrounding them, they can also be separated according to shape, Lavrentovich added.

"It turns out that this is important for the propulsion," he said. "A perfect sphere might cause one type of distortion, but a sphere with a tail – like a spermatozoid – would cause a different form of distortion. So that is sorting based on the shape of the particle rather than the charge."

The researchers have begun work investigating the use of water-based liquid crystal media, which, Lavrentovich noted, would probably be required for any applications of the method to proteomics work.

"There are liquid crystals called lyotropic [liquid crystals] that are based on water solutions of organic materials, and we hope that we can interface particles of biological origin like cells or proteins with these types of liquid crystals," he said.

With regard to the potential costs of such a method, Lavrentovich said he didn't expect that price would be an issue, noting that "[liquid crystals] are not that expensive" and that "the cost of lyotropic [liquid crystals] is often even lower, as we are talking about materials in which 50 percent to 90 percent of the content is just water."

Lavrentovich didn't offer a timeline for commercial applications of the method, saying that the publication was "just a first small step."

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