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!
SF State astronomer searches for signs of life on Wolf 1061 exoplanet
20.01.2017 | San Francisco State University
Molecule flash mob
19.01.2017 | Technische Universität Wien
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...
Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales
Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
19.01.2017 | Event News
10.01.2017 | Event News
09.01.2017 | Event News
20.01.2017 | Awards Funding
20.01.2017 | Materials Sciences
20.01.2017 | Life Sciences