A glucose biofuel cell which offers the best performance yet is reported in a study in Nature Communications this week. The cell, created by wiring glucose oxidase and laccase enzymes in a carbon nanotube disc, may provide a way of efficiently producing energy from clean sources. Biofuel cells use enzymes to produce energy at room temperature and neutral pH, alleviating the use of fossil fuels. Previous attempts to create glucose biofuel cells have resulted in cells of poor power output that are unstable over time. Serge Cosnier and colleagues now report a biofuel cell that uses carbon nanotubes for the direct transfer of electrons from the enzyme to the electrode surface. This results in a power density of up to 1.3 milliwatts per centimetre squared and an open circuit voltage of 0.95 V which is stable for at least one month. This makes the biofuel cell the most efficient system reported so far.