'Critical baby step' taken for spying life on a molecular scale

The ability to image single biological molecules in a living cell is something that has long eluded researchers; however, a novel technique, using the structure of diamond, may well be able to do this and potentially provide a tool for diagnosing, and eventually developing a treatment for, hard-to-cure diseases such as cancer.

In a study published today, Thursday, 19 May, in the Institute of Physics and the German Physical Society's New Journal of Physics, researchers have developed a technique, exploiting a specific defect in the lattice structure of diamond, to externally detect the spins of individual molecules.

Magnetic Resonance Imaging (MRI) has already taken advantage of a molecule's spin to give clear snapshots of organs and tissue within the human body, however to get a more detailed insight into the workings of disease, the imaging scale must be brought down to individual biomolecules, and captured whilst the cells are still alive.

Co-lead author Professor Phillip Hemmer, Electrical & Computer Engineering, Texas A&M University, said, "Many conditions, such as cancer and aging, have their roots at the molecular scale. Therefore if we could somehow develop a tool that would allow us to do magnetic resonance imaging of individual biomolecules in a living cell then we would have a powerful new tool for diagnosing and eventually developing cures for such stubborn diseases."

To do this, the researchers, from Professor Joerg Wrachtrup's group at the University of Stuttgart and Texas A&M University, used a constructed defect in the structure of diamond called a nitrogen vacancy (NV)—a position within the lattice structure where one of the carbon atoms is replaced with a nitrogen atom.

Instead of bonding to four other carbon atoms, the nitrogen atom only bonds to three carbon atoms leaving a spare pair of electrons, acting as one of the strongest magnets on an atomic scale.

The most important characteristic of a diamond NV is that it has an optical readout—it emits bright red light when excited by a laser, which is dependent on which way the magnet is pointing.

The researchers found that if an external spin is placed close to the NV it will cause the magnet to point in a different direction, therefore changing the amount of light emitted by it.

This change of light can be used to gauge which way the external molecule is spinning and therefore create a one-dimensional image of the external spin. If combined with additional knowledge of the surface, or a second NV nearby, a more detailed image with additional dimensions could be had.

To test this theory, nitrogen was implanted into a sample of diamond in order to produce the necessary NVs. External molecules were brought to the surface of the diamond, using several chemical interactions, for their spins to be analyzed.

Spins that exist within the diamond structure itself have already been modelled, so to test that the spins were indeed external, the researchers chemically cleaned the diamond surface and performed the analysis again to prove that the spins had been washed away.

Professor Hemmer continued, "Currently, biological interactions are deduced mostly by looking at large ensembles. In this case you are looking only at statistical averages and details of the interaction which are not always clear. Often the data is taken after killing the cell and spreading its contents onto a gene chip, so it is like looking at snapshots in time when you really want to see the whole movie."

"Clearly there is much work to be done before we can, if ever, reach our long-term goal of spying on the inner workings of life on the molecular scale. But we have to learn to walk before we can run, and this breakthrough represents one of the first critical baby steps."

From Thursday, 19 May, the journal paper can be found at http://iopscience.iop.org/1367-2630/13/5/055004

1. For further information, a full draft of the journal paper or contact with one of the researchers, contact IOP Publishing Press Assistant, Michael Bishop:
Tel: 0117 930 1032
E-mail: Michael.bishop@iop.org

2. The published version of the paper "Sensing external spins with NV diamond" Grotz et al 2011 New J. Phys. 13 055004 will be freely available online from Thursday, 19 May.

It will be available at http://iopscience.iop.org/1367-2630/13/5/055004

3. New Journal of Physics publishes across the whole of physics, encompassing pure, applied, theoretical and experimental research, as well as interdisciplinary topics where physics forms the central theme.

4. IOP Publishing provides publications through which leading-edge scientific research is distributed worldwide. IOP Publishing is central to the Institute of Physics (IOP), a not-for-profit society. Any financial surplus earned by IOP Publishing goes to support science through the activities of IOP.Beyond our traditional journals programme, we make high-value scientific information easily accessible through an ever-evolving portfolio of community websites, magazines, conference proceedings and a multitude of electronic services. Focused on making the most of new technologies, we're continually improving our electronic interfaces to make it easier for researchers to find exactly what they need, when they need it, in the format that suits them best. Go to http://publishing.iop.org/.

5. The Institute of Physics is a scientific charity devoted to increasing the practice, understanding and application of physics.

It has a worldwide membership of around 40 000 and is a leading communicator of physics-related science to all audiences, from specialists through to government and the general public. Its publishing company, IOP Publishing, is a world leader in scientific publishing and the electronic dissemination of physics. Go to www.iop.org

6. The German Physical Society (DPG) with a tradition extending back to 1845 is the largest physical society in the world with more than 59,000 members. The DPG sees itself as the forum and mouthpiece for physics and is a non-profit organisation that does not pursue financial interests. It supports the sharing of ideas and thoughts within the scientific community, fosters physics teaching and would also like to open a window to physics for all those with a healthy curiosity.