Fuel Cell Taps Into Roach Power

Instead of looking at cockroaches as disgusting pests, some scientists see them as potentially helpful scouts. Because of the insects’ hardy constitution, these scientists envision outfitting the roaches with tiny sensors or cameras and sending them to collect data in conditions that are harmful or inaccessible to people. In a step toward creating such insect soldiers, researchers now report a small device that can generate electricity from sugar in a cockroach’s blood (J. Am. Chem. Soc., DOI: 10.1021/ja210794c).

Scientists already can remotely control a cockroach’s movement using a battery-powered device that stimulates the insect’s nervous system, says Daniel Scherson of Case Western Reserve University. “But the lifetime of a battery is limited,” he points out. To make controllable insects independent of a power source, Scherson and his team wanted to develop a biofuel cell that could harness a bug’s own metabolism.

Their cockroach biofuel cell is a bundle of thin carbon wires sealed inside a glass capillary tube. The cell is about 0.05 cm in diameter and a few centimeters long. To make up the cell’s anode, Scherson and his team coated the wires with two enzymes: trehalase to break the sugar trehalose into two glucose molecules and glucose oxidase to extract electrons from the glucose. To create the cathode, the researchers coated the wires with the enzyme bilirubin oxidase to shuttle the generated electrons to oxygen to produce water. Because the enzymes alone can’t efficiently transfer electrons to and from the electrode, the researchers also added an osmium complex to the carbon wires to act as an electron shuttle. The researchers selected trehalose, says Scherson, because of its high concentration in cockroach blood, 30 mM.

The researchers placed the tiny biofuel cell into an incision made in the abdominal cavity of a sedated female discoid cockroach (Blaberus discoidalis). Using a standard meter, they measured the power produced by the biofuel cell over 2.5 hours. The maximum power density they found was 55 µW/cm² at a potential of 0.2 V. Scherson admits that this is a low wattage but says it is sufficient to power microdevices such as those used to control a roach’s movement. He adds that the cockroaches seemed unharmed by the procedure, simply walking away after the sedative wore off.

Adam Heller of the University of Texas, Austin, who has developed biofuel cells using grapes, calls the study “an important milestone” toward developing power sources from metabolic chemistry in organisms. He thinks researchers also could use the cells to power miniature probes to study insect behavior. By using different enzymes on the wires, scientists could also develop biofuel cells to power small medical devices.

Scherson and his colleagues next plan to test the biofuel cell’s ability to power tiny devices, such as blinking lights, which they will mount on cockroaches.