Apparently, the prime motivation for listening to individual neurons or brain cells is to “better understand the computational complexity of the brain,” according to a June 20, 2013 news item on Azonano,
The new brain cell spear is a millimeter long, only a few nanometers wide and harnesses the superior electromechanical properties of carbon nanotubes to capture electrical signals from individual neurons.
“To our knowledge, this is the first time scientists have used carbon nanotubes to record signals from individual neurons, what we call intracellular recordings, in brain slices or intact brains of vertebrates,” said Bruce Donald, a professor of computer science and biochemistry at Duke University who helped developed the probe.
The June 19, 2013 Duke University news release by Ashley Yeager, which originated the news item, provides some insight into the current state of the art and how this new technique is an improvement,
Currently, they use two main types of electrodes, metal and glass, to record signals from brain cells. Metal electrodes record spikes from a population of brain cells and work well in live animals. Glass electrodes also measure spikes, as well as the computations individual cells perform, but are delicate and break easily.”The new carbon nanotubes combine the best features of both metal and glass electrodes. They record well both inside and outside brain cells, and they are quite flexible. Because they won’t shatter, scientists could use them to record signals from individual brain cells of live animals,” said Duke neurobiologist Michael Platt, who was not involved in the study.
This is not the first time researchers have tried to use carbon nanotubes for this purpose, from the news release,
In the past, other scientists have experimented with carbon nanotube probes. But the electrodes were thick, causing tissue damage, or they were short, limiting how far they could penetrate into brain tissue. They could not probe inside individual neurons.
To change this, Donald began working on a harpoon-like carbon-nanotube probe with Duke neurobiologist Richard Mooney five years ago. The two met during their first year at Yale in the 1976, kept in touch throughout graduate school and began meeting to talk about their research after they both came to Duke.
Mooney told Donald about his work recording brain signals from live zebra finches and mice. The work was challenging, he said, because the probes and machinery to do the studies were large and bulky on the small head of a mouse or bird.
With Donald’s expertise in nanotechnology and robotics and Mooney’s in neurobiology, the two thought they could work together to shrink the machinery and improve the probes with nano-materials.
To make the probe, graduate student Inho Yoon and Duke physicist Gleb Finkelstein used the tip of an electrochemically sharpened tungsten wire as the base and extended it with self-entangled multi-wall carbon nanotubes to create a millimeter-long rod. The scientists then sharpened the nanotubes into a tiny harpoon using a focused ion beam at North Carolina State University.
Yoon then took the nano-harpoon to Mooney’s lab and jabbed it into slices of mouse brain tissue and then into the brains of anesthetized mice. The results show that the probe transmits brain signals as well as, and sometimes better than, conventional glass electrodes and is less likely to break off in the tissue. The new probe also penetrates individual neurons, recording the signals of a single cell rather than the nearest population of them.
Based on the results, the team has applied for a patent on the nano-harpoon. Platt said scientists might use the probes in a range of applications, from basic science to human brain-computer interfaces and brain prostheses.
Donald said the new probe makes advances in those directions, but the insulation layers, electrical recording abilities and geometry of the device still need improvement.
The research paper is available in the open access journal PLoS ONE,
Intracellular Neural Recording with Pure Carbon Nanotube Probes by Inho Yoon, Kosuke Hamaguchi, Ivan V. Borzenets, Gleb Finkelstein, Richard Mooney, and Bruce R. Donald. 2013. PLOS ONE. DOI: 10.1371/journal.pone.0065715
As for calling this a ‘harpoon’, these carbon nanotube probes really do resemble harpoons,You can compare it to this harpoon from The Specialists Prop House, Traditional harpoon page, I have written about some of the neuroscience work coming out of Duke University in the past, e.g., my March 4, 2013 posting about Miguel Nicolelis’ work on brain-to-brain communication.