Researchers are on the path to creating nano-MRI images

Dec 22, 2009 By Anne Ju and Bill Steele
A schematic of John Marohn's scanned-probe electron spin resonance experiments, with the oscillating cantilever in the middle and the nickel tip that was attached by hand. Image: Eric Moore

(PhysOrg.com) -- Cornell researchers are devising methods to detect the magnetic fields of individual electrons and atomic nuclei, which they hope to use to make a nanoscale version of magnetic resonance imaging.

In biochemistry, shape is everything. Because of the shape of their binding sites, hormones can attach to cell membranes to send signals inside, and viruses can open up paths to invade. But understanding the structure of complex molecules, sometimes made of tens of thousands of atoms, is no easy task. Existing microscopes, even the world's best electron microscopes, can't resolve atomic details of .

Researchers at Cornell are changing that: They are devising methods to detect the magnetic fields of individual electrons and atomic nuclei, which they hope to use to make 3-D images -- a nanoscale version of . Their new approach can detect a tiny force called electron spin to a sensitivity scale of about 400 electrons.

Their breakthrough is reported in the Dec. 14 online issue of .

"There is no more longstanding a problem than imaging the structure of membrane proteins," said John Marohn, associate professor of chemistry, who is leading the research and has been working on the problem for nearly a decade. "There is no general approach, and it is backbreaking work." Marohn belongs to a growing community of scientists doing single-molecule imaging, and in August Cornell hosted a conference on the topic.

At the heart of Marohn's research is the idea that electrons, protons and neutrons create a , also called a magnetic moment. When placed next to a stronger magnetic field, all the little "magnets" -- electrons or and in the nuclei -- line up. Applying a radiofrequency field tuned to the electron or nucleus causes the magnetic moment to spin off axis like a wobbly top, a behavior called precession.

A medical MRI machine detects voltage induced in a coil by the precession of, typically, a thousand billion hydrogen atoms, which creates enough resolution for 3-D imaging of body parts. Marohn and colleagues are trying to make an instrument sensitive enough to feel the force of a single electron or nucleus in a protein.

In their paper, they describe their new approach, which involves detecting the spin of electrons in a molecule called a nitroxide -- rare because it contains a radical, or an unpaired electron. Their technique opens up the possibility of imaging, at sub-nanometer resolution, the locations of nitroxide "labels" attached to individual protein molecules.

By creating a sample of nitroxide molecules dissolved in a thin-film polymer and bringing the sample close to a 4-micron nickel magnet attached to a 350-nanometer silicon cantilever, they can detect the electron spin by measuring the frequency of the cantilever as it wobbles, like a diving board. The cantilever is similar to those used in scanning probe microscopy, a type of imaging that involves a cantilever scanning a surface and recording the probe-surface interactions.

To improve their frequency readouts and get more accurate measurements, the group must learn, among others things, how to make their magnets smaller, Marohn said.

"The dream is to take that signal, run it through some sort of complicated algorithm, and get a picture," Marohn said.

Explore further: Heat makes electrons spin in magnetic superconductors

Related Stories

Spin-polarized electrons on demand

Jan 21, 2009

Many hopes are pinned on spintronics. In the future it could replace electronics, which in the race to produce increasingly rapid computer components, must at sometime reach its limits. Different from electronics, where whole ...

Spin-polarized electrons on demand

Jan 15, 2009

Many hopes are pinned on spintronics. In the future it could replace electronics, which in the race to produce increasingly rapid computer components, must at sometime reach its limits. Different from electronics, where whole ...

Recommended for you

Heat makes electrons spin in magnetic superconductors

Apr 24, 2015

Physicists have shown how heat can be exploited for controlling magnetic properties of matter. The finding helps in the development of more efficient mass memories. The result was published yesterday in Physical Review Le ...

ICARUS neutrino experiment to move to Fermilab

Apr 23, 2015

A group of scientists led by Nobel laureate Carlo Rubbia will transport the world's largest liquid-argon neutrino detector across the Atlantic Ocean from CERN to its new home at the US Department of Energy's ...

National security on the move with high energy physics

Apr 23, 2015

Scientists are developing a portable technology that will safely and quickly detect nuclear material hidden within large objects such as shipping cargo containers or sealed waste drums. The researchers, led ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

forumid01
5 / 5 (1) Dec 22, 2009
What's the difference between IBM's FMRI and Cornell's work? They look quite the same stuff?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.