Interdisciplinary Team Observes Brain Activity Using Premiere Quantum Dot Sensor

Luminescent quantum dots are finding new and exciting applications in current nanoscience research, including improved solar energy collectors, LEDs and quantum computers. A recent thrust from the U.S. Naval Research Laboratory’s Nanoscience Institute is focused on applying them as tools for neuroscience, opening the doors for a new way to observe brain activity and its functions.

An interdisciplinary group of NRL researchers led by Research Biologist Dr. James Delehanty developed the first sensor to use quantum dots to monitor the brain by reading its electrical signals, resulting in a less invasive process than the usual nanowire techniques. Monitoring the brain in this way can help scientists to better diagnose brain disorders that affect the warfighter, such as traumatic brain injury. The implications of this breaking research, in the context of QD properties, was recently highlighted in a perspective published in Nature Nanotechnology in early April.

Pictured left to right are NRL researchers Drs. Igor Medintz, Alexander Efros, Alan Huston, and James Delehanty in front of a customized fluorescence microscope equipped for microinjection of quantum dots and other nanoparticles into living cells.

The primary way we understand how the brain works is by looking at the electrical activity of the neurons in the brain. This is how neurons “talk” to one another.

“Currently, the available set of probes and materials for monitoring brain activity have limitations such as limited light output or they are inherently toxic,” said Dr. Igor Medintz, the Navy’s Senior Scientist for Biosensors and Biomaterials at NRL.

According to Medintz, developing new materials to look at this communication has been one avenue to address this problem.

“You need a material that can do two things,” Delehanty added. “The material needs to engage that electrical process [in the brain] and give you some type of output that you can see optically through a microscope.”

The team at NRL knew that quantum dots would be an excellent candidate for this application due to their ability to give off light, something you can see, in conjunction with their sensitivity to respond to the electrical signals routing through the brain. QDs are very much like “artificial atoms,” having unique properties that can be engineered for specific applications such as the color of the emitted light, by controlling the QD’s size, and the sensitivity to electric or magnetic fields by controlling structure and composition.

“Quantum dots have a lot of advantages,” said Delehanty. “They’re much brighter, they’re much more stable, and they can be designed to engage the electrical process appropriately.”

Photo by Gabrielle Gibert, Strategic Communications

Dr. James Delehanty demonstrates the use of the cell microinjection system.

NRL used these advantages and combined them with a nanomaterial called a carbon buckyball or fullerene through the use of a peptide in order to create a sensor that is able to attach itself to the membrane of a nerve cell. The sensor then gives off different levels of light in response to changing electrical signals in the brain.

“When the sensor sits in the [cell] membrane and an electrical pulse occurs, the quantum dot goes from bright to dim, then brightens again as the pulse passes,” said Delehanty. “In the brain, you get lots and lots of these events happening in a very confined space, so you see this time-resolved brightness or luminescence change."

Using these sensors to discover how the brain works is integral to the warfighter for a number of reasons, from diagnosing traumatic brain injury to neural interfacing “like the stuff of science fiction where you could get computer readouts in your brain,” according to Medintz.

While those specific technologies are still far off in the future, this particular quantum dot sensor has been reduced to practice and demonstrated through a collaboration with the Howard Hughes Medical Institute Janelia Farms Research Campus. This partnership also highlights NRL’s ability to team up with outside academic and scientific institutions in pursuit of cutting edge research.

According to Delehanty, this project feeds into the DoD’s larger interest in studying the brain. “There are huge research initiatives currently underway to learn how the brain works,” said Delehanty. “And the first part of those initiatives are focused on developing the tools to be able to see the brain. Once we can see the brain at the smallest level and the biggest level then we can have the ability to start dissecting how the brain works.”

The quantum dot sensors fashioned by Delehanty’s interdisciplinary team bring us one step closer to achieving this goal.

The team consists of biologists Medintz and Delehanty, Dr. Alan Huston from the Optical Sciences Division, and Dr. Alexander Efros who is the Navy’s Senior Scientist for Computational Material from the Material Science and Technology Division, as well as contributions from a 20-year collaboration between NRL’s Optical Science Division and the Center for Biomolecular Science and Engineering.

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