Big step toward tiny biological “batteries”
By growing nanoscale wire brushes-built of the body's own molecules-that conduct electrical charges, University of Georgia researchers have taken a first step toward developing biological fuel cells that could ultimately power pacemakers, cochlear implants, and prosthetic limbs.
The journal Chemical Science called the technique "a significant breakthrough for nanotechnology." UGA chemist Jason Locklin and graduate students Nicholas Marshall and Kyle Sontag fabricated brushes made up of chains of thiophene and benzene molecules that ranged in thickness from 5 to 50 nanometers, too small to see even under a high-powered optical microscope.
"These molecular wires are actually polymer chains that have been grown from a metal surface at very high density," said Locklin, who has a joint appointment with UGA's Franklin College of Arts and Sciences and the Faculty of Engineering and is a member of the Nanoscale Science and Engineering Center. "The structure of the film resembles a toothbrush, where the chains of conjugated polymers are like the bristles. To get chains to pack tightly in extended conformations, they must be grown from the surface, a method we call the ‘grafting from' approach."
Using this approach, the scientists laid down a single layer of thiophene as the film's initial coating, then built up chains of thiophene or benzene using a controlled polymerization technique.
Their research, funded by the Petroleum Research Foundation, was published in the June issue of Chemical Communications.
While a major goal is to develop biofuel cells that would replace the need for batteries in an implanted device, it's difficult to harness the body's own fuel sources. While enzymes, for example, do a good job of converting chemical energy into electrical energy, "they aren't very useful in this application because they have natural protective insulating layers that prevent good electron transport from active site to electrode," Locklin said. "Hopefully, our molecular wires will provide a better conduit for charges to flow.
"The beauty of organic semiconductors is how their properties change, based on size and the number of repeating units," he said. Thiophene itself is an insulator, "but by linking many thiophene molecules together in a controlled fashion, the polymers have conducting properties." Moreover, "because this technique allows us to systematically vary polymer architecture," said Locklin, "it opens up the possibility for use in electronic devices such as sensors, transistors, and photovoltaics."
There is a long way to go, however. While "flexible electronics" is a large and promising area of research, it is still in its infancy, Locklin said. "For example, we don't yet understand all of the fundamental physics involved in how electrical charges move through organic materials."