Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Lollipops and ice fishing: Molecular rulers used to probe nanopores

30.04.2010
Using a pair of exotic techniques including a molecular-scale version of ice fishing, a team of researchers working at the National Institute of Standards and Technology (NIST) have developed methods to measure accurately the length of "nanopores," the miniscule channels found in cell membranes.

The "molecular rulers" they describe in a recent paper* could serve as a way to calibrate tailor-made nanopores—whose diameters on average are nearly 10,000 times smaller than that of a human hair—for a variety of applications such as rapid DNA analysis.

Studies at NIST and other research institutions have shown that a single nanometer-scale pore in a thin membrane can be used as a "miniature analysis laboratory" to detect and characterize individual biological molecules such as DNA or toxins as they pass through or block the passage. Such a system could potentially fit on a single microchip device, for a wide variety of applications. However, making the mini-lab practical requires an accurate definition of the dimensions and structural features of the nanopore.

In new experiments, researchers from NIST and the University of Maryland first built a membrane—a bilayer sheet of lipid molecules—similar to that found in animal cells. They "drilled" a pore in it with a protein** designed specifically to penetrate cell membranes. When voltage is applied across the membrane wall, charged molecules such as single-stranded DNA are forced into the nanopore. As the molecule passes into the channel, the ionic current flow is reduced for a time that is proportional to the size of the chain, allowing its length to be easily derived.

If a chain is long enough to reach the narrowest part of the nanopore—known as the pinch point—the force of the electrical field behind it will push the molecule on through the rest of the channel. Exploiting this characteristic, the NIST/Maryland team developed a DNA probe method to measure the distances from the openings on each side of the membrane to the pinch point, and in turn, the entire length of the nanopore by adding the two measurements together. The probes consist of DNA strands of known lengths topped on one end by a polymer sphere. The sphere prevents the probe from completely moving through the nanopore while leaving the DNA chain dangling from it free to extend into the channel. If the chain reaches the pinch point, the force that would normally drive a free DNA chain past the junction instead holds the probe in place (since the polymer sphere "locks" it at the other end) and defines the distance to the pinch point. If the chain is shorter than the distance to the pinch point, it will be bounced out of the nanopore, telling researchers that a longer-length chain is needed to measure the distance to the gap.

The NIST/Maryland researchers also developed a second means of measuring the length of the nanopore to confirm the results of the "single lollipop" method. In this system, polymer molecules are allowed to circulate freely in the solution found on the inner side of the membrane. Polymer-capped DNA probes of different lengths are forced one at a time into the nanopore from the opposite side. If the end of a probe's chain is long enough to completely transverse the channel, it will grab hold of a free polymer molecule in solution. This defines the length of the channel.

Additionally, this "ice fishing" method provides insight into the structure of the nanopore. As the DNA chain winds its way through, changes in electrical voltage correspond to the changing shape of the channel. This information can be used to effectively map the passageway.

* S.E. Henrickson, E.A. DiMarzio, Q. Wang, V.M. Stanford and J.J. Kasianowicz. Probing single nanometer-scale pores with polymeric molecular rulers. The Journal of Chemical Physics 132, 135101 (published online April 2, 2010).

** Alpha-hemolysin, produced by the Staphylococcus aureus bacteria

Michael E. Newman | EurekAlert!
Further information:
http://www.nist.gov

Further reports about: DNA DNA strand Lollipops Molecular Target NIST NIST/Maryland cell membrane polymer molecule

More articles from Physics and Astronomy:

nachricht New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center

nachricht Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>