Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

DNA separation by entropic force offers better resolution

24.09.2002


Scanning electron micrograph of a cross section of the finished device. An array of densely spaced nanopillars constitutes the entropically unfavorable region. The pillar spacing was 135 nm and their width approximately 80 nm. Copyright © Cornell


Fluorescing DNA molecules show the separation of two different lengths of DNA. In the first image, DNA molecules pulled by a weak electric field gather at the edge of a sieve made of tiny pillars. After a stronger field pulse of two seconds, the shorter molecules were fully inserted, while the longer molecules remained partially in the open, entropically favorable region. When the field was removed, the longer molecules extracted themselves from the pillar region, as shown at right. Copyright © Cornell University


Cornell University researchers have demonstrated a novel method of separating DNA molecules by length. The technique might eventually be used to create chips or other microscopic devices to automate and speed up gene sequencing and DNA fingerprinting.

The method, which uses a previously discovered entropic recoil force, has better resolution -- that is, better ability to distinguish different lengths -- than others tried so far, the researchers say. They separated DNA strands of two different lengths, using their own nanofabricated device, and demonstrated that modifications would make it possible to separate strands of many different lengths.

A description of the experiment is scheduled to be published in the Oct. 1, 2002, issue of the journal Analytical Chemistry by graduate student Mario Cabodi, postdoctoral researcher Stephen Turner and Harold Craighead, the C.W. Lake Jr. Professor of Productivity.



The traditional method of separating DNA is gel electrophoresis, in which a strand is cut into many pieces and passed through a porous gel, where shorter lengths will move faster and farther than longer ones. From the distribution of the fragments, information about the genetic content can be determined. Researchers at Cornell and elsewhere have been experimenting with a variety of devices that replace the porous gel with microscopic sieves made by the same techniques used to manufacture electronic circuits.

Previously, Turner, Cabodi and Craighead studied the physics governing the movement of molecules through these sieves. Ordinarily, a long chain DNA molecule in liquid will clump into a roughly spherical shape, and to move through a sieve it must uncoil and slide in lengthwise. The researchers found that this movement involves an entropic force which causes DNA molecules that are only partially within a sieve to withdraw when the force pulling them in -- an electric field -- is removed. The effect is similar to a slippery chain falling from a table. If the chain is either entirely on the table or entirely on the floor, it will not move, but if part of it is hanging over the edge of the table it will eventually all spill onto the floor. In the case of DNA molecules in liquid, the effect results from the motion of segments in the chain molecule as they interact with the beginning of the barrier. The force is called "entropic" because the molecule moves out of the restricted space of the sieve into an open area where it can be more disordered.

In the latest experiment, the researchers used the Cornell Nanofabrication Facility (CNF) to make a sieve consisting of a forest of tiny pillars 80 nanometers wide, spaced about 135 nanometers apart, just large enough for a DNA molecule to pass through lengthwise. (A nanometer is a billionth of a meter, approximately three times the diameter of a silicon atom.) The researchers inserted a mix of DNA strands of two different lengths in a space next to the pillars and applied an electric field in a short pulse. The length of the pulse was adjusted so that shorter molecules were able to move completely into the pillar region, while longer ones could move only partway in. When the field was turned off, the longer strands recoiled, while the shorter ones, completely inside the pillar region, did not.

DNA molecules are too small to be observed directly, but for the experiment they were stained with a fluorescent dye, and the light given off was visible under a conventional microscope.

In further tests, the researchers showed that by applying a series of pulses of different durations the method could be used to separate strands of many different lengths. Another approach to separating strands of many lengths, they said in their paper, might be a "cascade" of similar separation devices. These methods would also improve the resolution, they said. They predicted that such a device could separate DNA molecules "in a particularly challenging length range with higher resolution than any other known method."

The principle of entropic recoil, they said, also could be applied by using various types of porous membranes and ceramic filters, as well as nanofabricated sieves. The technique could also be applied to proteins and other polymers, they added.

The paper in Analytical Chemistry is titled "Entropic Recoil Separation of Long DNA Molecules." The research was funded by the National Institutes of Health. CNF is supported by the National Science Foundation.

Bill Steele | Cornell News
Further information:
http://www.hgc.cornell.edu/index.html
http://www.news.cornell.edu/releases/May02/entropic.ws.html
http://www.news.cornell.edu/releases/Sept02/One_step_separation.avi

More articles from Life Sciences:

nachricht Cells migrate collectively by intermittent bursts of activity
30.09.2016 | Aalto University

nachricht The structure of the BinAB toxin revealed: one small step for Man, a major problem for mosquitoes!
30.09.2016 | CNRS (Délégation Paris Michel-Ange)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: First-Ever 3D Printed Excavator Project Advances Large-Scale Additive Manufacturing R&D

Heavy construction machinery is the focus of Oak Ridge National Laboratory’s latest advance in additive manufacturing research. With industry partners and university students, ORNL researchers are designing and producing the world’s first 3D printed excavator, a prototype that will leverage large-scale AM technologies and explore the feasibility of printing with metal alloys.

Increasing the size and speed of metal-based 3D printing techniques, using low-cost alloys like steel and aluminum, could create new industrial applications...

Im Focus: New welding process joins dissimilar sheets better

Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of light metals.
Scientists at the University of Stuttgart have now developed two new process variants that will considerably expand the areas of application for friction stir welding.
Technologie-Lizenz-Büro (TLB) GmbH supports the University of Stuttgart in patenting and marketing its innovations.

Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of...

Im Focus: First quantum photonic circuit with electrically driven light source

Optical quantum computers can revolutionize computer technology. A team of researchers led by scientists from Münster University and KIT now succeeded in putting a quantum optical experimental set-up onto a chip. In doing so, they have met one of the requirements for making it possible to use photonic circuits for optical quantum computers.

Optical quantum computers are what people are pinning their hopes on for tomorrow’s computer technology – whether for tap-proof data encryption, ultrafast...

Im Focus: OLED microdisplays in data glasses for improved human-machine interaction

The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.

“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...

Im Focus: Artificial Intelligence Helps in the Discovery of New Materials

With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.

Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Paper – Panacea Green Infrastructure?

30.09.2016 | Event News

HLF: From an experiment to an establishment

29.09.2016 | Event News

European Health Forum Gastein 2016 kicks off today

28.09.2016 | Event News

 
Latest News

First-Ever 3D Printed Excavator Project Advances Large-Scale Additive Manufacturing R&D

30.09.2016 | Materials Sciences

New Technique for Finding Weakness in Earth’s Crust

30.09.2016 | Earth Sciences

Cells migrate collectively by intermittent bursts of activity

30.09.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>