Researchers develop new method to control nanoscale diamond sensors

January 24, 2014 by Helen Knight
A single nitrogen-vacancy (N-V) center in diamond (right, inset), optically initialized and readout by confocal microscopy, is manipulated with coherent control sequences (red line) of microwave pulses. This measures the arbitrary profile of time-varying magnetic fields radiated by biological sources (or by artificial sources in the researchers' proof-of-principle experiment). Credit: Paola Cappellaro

Diamonds may be a girl's best friend, but they could also one day help us understand how the brain processes information, thanks to a new sensing technique developed at MIT.

A team in MIT's Quantum Engineering Group has developed a new method to control nanoscale diamond sensors, which are capable of measuring even very weak magnetic fields. The researchers present their work this week in the journal Nature Communications.

The new control technique allows the tiny sensors to monitor how these magnetic fields change over time, such as when neurons in the brain transmit electrical signals to each other. It could also enable researchers to more precisely measure the magnetic fields produced by novel materials such as the metamaterials used to make superlenses and "invisibility cloaks."

In 2008 a team of researchers from MIT, Harvard University, and other institutions first revealed that nanoscale defects inside diamonds could be used as magnetic sensors.

The naturally occurring defects, known as nitrogen-vacancy (N-V) centers, are sensitive to external magnetic fields, much like compasses, says Paola Cappellaro, the Esther and Harold Edgerton Associate Professor of Nuclear Science and Engineering (NSE) at MIT.

Defects inside are also known as color centers, Cappellaro says, as they give the gemstones a particular hue: "So if you ever see a nice diamond that is blue or pink, the color is due to the fact that there are defects in the diamond."

The N-V center defect consists of a nitrogen atom in place of a carbon atom and next to a vacancy—or hollow—within the diamond's lattice structure. Many such defects within a diamond would give the gemstone a pink color, and when illuminated with light they emit a red light, Cappellaro says.

To develop the new method of controlling these sensors, Cappellaro's team first probed the diamond with green laser light until they detected a red light being emitted, which told them exactly where the defect was located.

They then applied a microwave field to the nanoscale sensor, to manipulate the of the N-V center. This alters the intensity of light emitted by the defect, to a degree that depends not only on the microwave field but also on any external magnetic fields present.

To measure and how they change over time, the researchers targeted the nanoscale sensor with a microwave pulse, which switched the direction of the N-V center's electron spin, says team member and NSE graduate student Alexandre Cooper. By applying different series of these pulses, acting as filters—each of which switched the direction of the electron spin a different number of times—the team was able to efficiently collect information about the external .

They then applied signal-processing techniques to interpret this information and used it to reconstruct the entire magnetic field. "So we can reconstruct the whole dynamics of this external magnetic field, which gives you more information about the underlying phenomena that is creating the magnetic field itself," Cappellaro says.

The team used a square of diamond three millimeters in diameter as their sample, but it is possible to use sensors that are only tens of nanometers in size. The diamond sensors can be used at room temperature, and since they consist entirely of carbon, they could be injected into living cells without causing them any harm, Cappellaro says.

One possibility would be to grow neurons on top of the diamond sensor, to allow it to measure the magnetic fields created by the "action potential," or signal, they produce and then transmit to other nerves.

Previously, researchers have used electrodes inside the brain to "poke" a neuron and measure the electric field produced. However, this is a very invasive technique, Cappellaro says. "You don't know if the neuron is still behaving as it would have if you hadn't done anything," she says.

Instead, the diamond sensor could measure the magnetic field noninvasively. "We could have an array of these defect centers to probe different locations on the neuron, and then you would know how the signal propagates from one position to another one in time," Cappellaro says.

In experiments to demonstrate their sensor, the team used a waveguide as an artificial neuron and applied an external magnetic field. When they placed the diamond sensor on the waveguide, they were able to accurately reconstruct the magnetic field. Mikhail Lukin, a professor of physics at Harvard, says the work demonstrates very nicely the ability to reconstruct time-dependent profiles of weak magnetic fields using a novel magnetic sensor based on quantum manipulation of defects in diamond.  

"Someday techniques demonstrated in this work may enable us to do real-time sensing of brain activity and to learn how they work," says Lukin, who was not involved in this research. "Potential far-reaching implications may include detection and eventual treatment of brain diseases, although much work remains to be done to show if this actually can be done," he adds.

Explore further: A new spin in diamonds for quantum technologies

Related Stories

A new spin in diamonds for quantum technologies

December 20, 2011

(PhysOrg.com) -- To explore the future potential of diamonds in quantum devices, researchers from Macquarie University have collaborated with the University of Stuttgart and University of Ulm in Germany towards developing ...

Nanoscale MRI being developed

February 1, 2013

(Phys.org)—Two independent groups of scientists in the U.S. and Germany have reduced magnetic resonance imaging (MRI) down to the nanoscale, which may enable them in the future to non-destructively detect and image small ...

Spinach and nanodiamonds?

October 3, 2013

Popeye, the comic book hero, swears by it as do generations of parents who delight their children with spinach. Of course, today it is known that the vegetable is not quite as rich in iron as originally thought, but that ...

Manipulating electron spin mechanically

December 4, 2013

(Phys.org) —Contrary to many textbook illustrations, electrons aren't just balls floating around an atom. In quantum theory, they're more like little tops, exhibiting "spin," and each creating its own tiny magnetic field.

Recommended for you

For 2-D boron, it's all about that base

September 2, 2015

Rice University scientists have theoretically determined that the properties of atom-thick sheets of boron depend on where those atoms land.

Electrical circuit made of gel can repair itself

August 25, 2015

(Phys.org)—Scientists have fabricated a flexible electrical circuit that, when cut into two pieces, can repair itself and fully restore its original conductivity. The circuit is made of a new gel that possesses a combination ...

An engineered surface unsticks sticky water droplets

August 31, 2015

The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets ...

Scientists grow high-quality graphene from tea tree extract

August 21, 2015

(Phys.org)—Graphene has been grown from materials as diverse as plastic, cockroaches, Girl Scout cookies, and dog feces, and can theoretically be grown from any carbon source. However, scientists are still looking for a ...

0 comments

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.