Researchers at the University of Georgia (UGA; Athens) have developed a method for growing molecular wire brushes that conduct electrical charges. Made up of chains of thiophene and benzene attached to metal surfaces as ultrathin films, the brushes could lead to the fabrication of biological fuel cells that may one day power devices that interface with living tissue, such as pacemakers, cochlear implants, prosthetic limbs, and biochemical sensors.

“The molecular wires are actually polymer chains that have been grown from a metal surface at very high density,” remarks Jason Locklin, a UGA chemist who has spearheaded the research together with graduate students Nicholas Marshall and Kyle Sontag. “The structure of the film resembles a toothbrush, where the chains of conjugated polymers are like the bristles. We call these types of coatings polymer brushes. To get chains to pack tightly in extended conformations, they must be grown from the surface, a method we call the ’grafting from‘ approach.”

To make the polymer brushes, the scientists laid down a single layer of thiophene as the film‘s initial coating and then built up chains of thiophene or benzene using a controlled polymerization technique. “This technique gives us the control to systematically vary polymer architecture, opening up the possibility for various uses in electronic devices such as sensors, transistors, and diodes,” notes Locklin. Ranging in size from 5 to 50 nm, the ultrathin films are too small to see, even with the aid of a high-powered optical microscope.

While flexible electronics is a large and growing area of research, it‘s still in its infancy, Locklin says. “For example, we don‘t yet understand all of the fundamental physics involved in how electrical charges move through organic materials.”