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 Epoxy compound gets a graphene bump
14.11.2018 | Rice University

nachricht Automated adhesive film placement and stringer integration for aircraft manufacture
15.11.2018 | Fraunhofer IFAM

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>