Scientists have used carbon nanotubes to engineer an astonishingly small electrode, pictured here, that is thin and long enough to record electrical activity within individual neurons.
The single cell resolution, in and of itself, is not unprecedented (we've been measuring single-neuron activity with glass pipettes for years, using a Nobel Prize winning technique called the patch clamp method); the use of carbon nanotubes, however, is. Carbon nanotubes are cylinders of the much-touted wondermaterial graphene – one-atom-thick sheets of carbon with remarkable properties. Writes Duke University's Inho Yoon, first author of the study describing the novel recording device, which is published in last week's PLoS ONE:
"Although glass electrodes are widely used for intracellular recordings, novel electrodes with superior mechanical and electrical properties are desirable, because they could extend intracellular recording methods to challenging environments, including long term recordings in freely behaving animals."
Carbon nanotubes demonstrate high electrical conductance (which makes them great for recording neuronal activity), remarkable mechanical strength (so they won't snap off inside your brain) and electrochemical stability. They also play nice with biological tissues.
Until now, however, carbon nanotube probes have been too short or wide to be of any use to researchers who would use them to monitor neuronal activity. No longer.
The probe designed by Yoon and his colleagues measures between just 5 and 10 micrometers wide – about the diameter of a red blood cell. And yet, it's roughly a millimeter long, and could, in theory, be made even longer. Tech Review's Susan Young has details on the research team's demonstration of the device:
The team was able to detect small changes in electrical activity in the cell—changes corresponding to the input signals the neuron was receiving from other neurons. An average cortical neuron can receive signals from around 10,000 other neurons, says Richard Mooney, a neuroscientist at Duke University and an author on the study. “Individually, those generate very small signals,” he says. Together, the collection of signals is computed by the receiving neuron as it decides whether or not to fire.
Intracellular recordings could be useful for mapping the functional connections between neurons, a goal of the recently launched BRAIN initiative (see “The Brain Activity Map”). “By being able to look inside the cell and measure small voltage changes, you get access to the network that talks to that cell,” say Mooney.