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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.