Nuts and Volts - September 2013

Harpoon Your Brain

If you want to monitor overall brain activity, the standard way is to strap a headset on the victim, hook him up to an electroencephalography (EEG) apparatus, and watch what comes through the channels. Sometimes, though, scientists want to study interactions between individual neurons to, e.g., better understand the computational complexity of the brain.

That can be a little tricky as it involves inserting tiny electrodes into the cells, and existing ones have some shortcomings.

Metal electrodes record spikes but can't record the computations performed by the cells. Glass probes can do both but are fragile and can break off, leaving your brain full of little shards.

Recently, a couple of professors at Duke University ( duke.edu) constructed a brain cell "nano-harpoon" out of increasingly ubiquitous carbon nanotubes. The result is an improved probe that is only a millimeter long and a few nanometers thick.

"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," noted Prof. Bruce Donald, one of the probe's developers. "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," added Duke neurobiologist Michael Platt.

To make the probe, they started with the tip of an electrochemically sharpened piece of tungsten wire and extended it with self-entangled multiwall carbon nanotubes, which were further sharpened using a focused ion beam.

They then jabbed it into mouse brains to demonstrate that this type of probe works at least as well as its glass counterparts — so well that the team has applied for a patent. According to the developers, the probes may be useful in applications ranging from basic science to human brain-computer interfaces and brain prostheses. ▲

ADVANCED TECHNOLOGY

■ Brain cell harpoon developed at Duke University.

Small Size, More Power

Also on the tiny side is a new microbattery developed by a research team from Harvard's Wyss Institute ( wyss.harvard.edu) and the University of Illinois at Urbana-Champaign ( illinois.edu). There has always been a tradeoff between the size of a battery and the amount of power it can provide, which is a limitation for many miniaturized devices such as flying insect-like robots, built-in microphones and cameras, and other gadgets for which weight is critical. One approach is to create very thin, lightweight batteries using thin-film deposition techniques. Because they are super thin, they just don't pack enough power for many designs. The Harvard/Illinois team reasoned that, if they could come up with inks that have the right combination of chemical and electrical properties, it would be possible to create more powerful batteries using 3D printing techniques. Turns out they were right.

They concocted one ink for the anodes and another for the cathodes — each containing a different lithium metal oxide compound. These were deposited as layers on two gold combs to create an interlaced stack of anodes and cathodes. Then, all they had to do was drop the electrodes into a container and fill it with electrolyte. The result is functioning lithium-ion microbatteries the size of a grain of sand.

According to one of the team members,

"The electrochemical performance is comparable to commercial batteries in terms of charge and discharge rate, cycle life, and energy densities.

We're just able to achieve this on a much smaller scale." This breakthrough should be useful in the development of many types of smaller devices in medical and other fields. ▲