Dr. Minteer recently demonstrated a glucose-fueled cell the size of a postage stamp that ran a calculator. The fuel cell contains enzymes that process the sugars into electricity and produce water. The cell is completely biodegradable after it's used up but there is no indication of what happens to the carbon in the glucose or whether it could be scaled up enough to power anything larger than consumer electronics devices. Dr. Minteer expects the cell to be commercialized in about three to five years.
[Source: Saint Louis University]