Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists channel graphene to understand filtration and ion transport into cells

11.12.2017

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules, particularly water, that have an affinity for the charged atoms. But these molecular processes have traditionally been difficult to model--and therefore to understand--using computers or artificial structures.


In this simulation, a biological membrane (gray) with an ion channel (center) is immersed in a solution of water and ions. This cross section of a simulation "box" shows the electric potential, the externally supplied "force" that drives ions through the channel. A dazzling pattern emerges in this potential due to the presence of the channel -- the colors show the lines of equal potential. The slowly decaying nature of this pattern in space makes simulations difficult. The golden aspect ratio -- the chosen ratio of height to width of this box -- allows for small simulations to effectively capture the effect of the large spatial dimensions of the experiment.

Credit: NIST

Now, researchers at the National Institute of Standards and Technology (NIST) and their colleagues have demonstrated that nanometer-scale pores etched into layers of graphene--atomically thin sheets of carbon renowned for their strength and conductivity--can provide a simple model for the complex operation of ion channels.

This model allows scientists to measure a host of properties related to ion transport. In addition, graphene nanopores may ultimately provide scientists with efficient mechanical filters suitable for such processes as removing salt from ocean water and identifying defective DNA in genetic material.

NIST scientist Michael Zwolak, along with Subin Sahu (who is jointly affiliated with NIST, the University of Maryland NanoCenter and Oregon State University), has also discovered a way to simulate aspects of ion channel behavior while accounting for such computationally intensive details as molecular-scale variations in the size or shape of the channel.

To squeeze through a cell's ion channel, which is an assemblage of proteins with a pore only a few atoms wide, ions must lose some or all of the water molecules bound to them. However, the amount of energy required to do so is often prohibitive, so ions need some extra help. They get that assistance from the ion channel itself, which is lined with molecules that have opposite charges to certain ions, and thus helps to attract them. Moreover, the arrangement of these charged molecules provides a better fit for some ions versus others, creating a highly selective filter. For instance, certain ion channels are lined with negatively charged molecules that are distributed in such a way that they can easily accommodate potassium ions but not sodium ions.

It's the selectivity of ion channels that scientists want to understand better, both to learn how biological systems function and because the operation of these channels may suggest a promising way to engineer non-biological filters for a host of industrial uses.

By turning to a simpler system--graphene nanopores--Zwolak, Sahu, and Massimiliano Di Ventra of the University of California, San Diego, simulated conditions that resemble the activity of actual ion channels. For example, the team's simulations demonstrated for the first time that nanopores could be made to permit only some ions to travel through them by changing the diameter of the nanopores etched in a single sheet of graphene or by adding additional sheets. Unlike biological ion channels, however, this selectivity comes from the removal of water molecules only, a process known as dehydration.

Graphene nanopores will allow this dehydration-only selectivity to be measured under a variety of conditions, another new feat. The researchers reported their findings in recent issues of Nano Letters and Nanoscale.

In two preprints (https://arxiv.org/abs/1708.03327 and https://arxiv.org/abs/1711.00472), Zwolak and Sahu address some of the complexity in simulating ions' constriction and transport through the nanopore channels. When theorists simulate a process, they choose a certain size "box" in which they perform those simulations. The box might be bigger or smaller, depending on the breadth and detail of the calculation. The researchers showed that if the dimensions of the simulation volume are chosen such that the ratio of the width of the volume to its height has a particular numerical value, then the simulation can simultaneously capture the influence of the surrounding ionic solution and such thorny details as nanoscale fluctuations in the diameter of the pores or the presence of charged chemical groups. This discovery--which the team calls "the golden aspect ratio" for simulations--will greatly simplify calculations and lead to a better understanding of the operation of ion channels, Zwolak said.

###

Papers: S. Sahu, M. Di Ventra, and M. Zwolak. Dehydration as a Universal Mechanism for Ion Selectivity in Graphene and Other Atomically Thin Pores. Nano Letters. Published online 5 July 2017. DOI: 10.1021/acs.nanolett.7b01399

S. Sahu and M. Zwolak. Ionic selectivity and filtration from fragmented dehydration in multilayer graphene nanopores. Nanoscale. Published online 25 July 2017. DOI: 10.1039/C7NR03838K

Media Contact

Ben Stein
bstein@nist.gov
301-975-2763

 @usnistgov

http://www.nist.gov 

Ben Stein | EurekAlert!
Further information:
https://www.nist.gov/news-events/news/2017/12/scientists-channel-graphene-understand-filtration-and-ion-transport-cells

More articles from Materials Sciences:

nachricht Machine-learning predicted a superhard and high-energy-density tungsten nitride
18.07.2018 | Science China Press

nachricht In borophene, boundaries are no barrier
17.07.2018 | Rice University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

NYSCF researchers develop novel bioengineering technique for personalized bone grafts

18.07.2018 | Life Sciences

Machine-learning predicted a superhard and high-energy-density tungsten nitride

18.07.2018 | Materials Sciences

Why might reading make myopic?

18.07.2018 | Health and Medicine

VideoLinks
Science & Research
Overview of more VideoLinks >>>