Posted: November 10, 2008 |
Researchers stimulate patchiness in phospholipid membranes with charged nanoparticles |
(Nanowerk News) Like water and ice cubes mixed in a glass, a group of organic compounds called lipids can coexist as liquid and solid in membranes. This patchiness in phospholipid membranes is fundamental to their use as biomolecules and biosensors.
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Using charged nanoparticles, researchers at the University of Illinois have found a new way to stimulate patchiness in phospholipid membranes.
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"We are seeing a previously unsuspected responsiveness in phospholipid membranes," said Steve Granick, a Founder Professor of Engineering at the U. of I. "What we thought was possible only with the specificity of certain proteins, we now see can happen with simple, charged nanoparticles."
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Lipids are the building blocks of cell membranes. In earlier work, Granick and graduate student Liangfang Zhang found a way to stabilize sensitive lipid membranes by attaching charged nanoparticles to the membrane surface.
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Steve Granick, a Founder Professor of Engineering at the U. of I., and colleagues have found that a group of organic compounds called lipids can coexist as liquid and solid in membranes. This patchiness in phospholipid membranes is fundamental to their use as biomolecules and biosensors.
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Now, Granick, Zhang, graduate research assistant Bo Wang and research scientist Sung Chul Bae show that a phospholipid membrane can coexist in two phases – solid and liquid – according to what binds to it. This inherent patchiness presents an additional mechanism for changing the stiffness of phospholipid membranes.
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The researchers report their work in a paper to be published next week in the Online Early Edition of the Proceedings of the National Academy of Sciences.
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Using fluorescence and calorimetry methods, the researchers studied interactions between charged nanoparticles and membranes formed from single-component lipids. Because the membrane was composed of one sole lipid type, the traditional explanation for spatial patchiness – an uneven distribution of different lipids – was eliminated.
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While a variety of nanoparticles was used, the most common type was polystyrene spheres about 20 nanometers in diameter (a nanometer is 1 billionth of a meter). Where the nanoparticles attached to the membrane, the membrane responded by changing phase.
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"The electric charge acted as a switch," Granick said. "Nanoparticles with a negative charge switched membranes from liquid to solid. Nanoparticles with a positive charge switched the membranes from solid to liquid."
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Phase changes occurred in patches of membranes where phospholipid molecules swiveled after binding to charged nanoparticles. This binding-induced behavior, where the same lipid can coexist in two different phases, offers a new mechanism for modulating stiffness in membranes.
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In future work, the researchers plan to study the effects of smaller, charged nanoparticles; the effects of charged nanoparticles on living cells; and novel ways to stabilize lipid membranes for targeted drug delivery.
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"These experiments are helping us better understand both the structure of phospholipid membranes and the potential biological effects of exposure to nanoparticles found in our normal, everyday environment," Granick said.
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