Nanotechnology has progressed to the point where miniaturized devices may soon be maneuvered within a person’s body to monitor or repair living tissue. One of the major challenges in this field is to find small but efficient sources of power for such devices.

A team of researchers led by Jing Zhu of Tsinghua University in Beijing, China, has now developed an ingenious new fuel cell that extracts power from biological fluids such as glucose or human blood.1 This ‘self-powered’ system could have applications in biomedicine, sensing, defense and even portable electronics.

Fig. 1: Schematic diagram showing the biofluid-powered, single-nanowire biofuel cell. The reactions catalyzed by the two enzymes (laccase and glucose oxidase, GOx) drive the flow of protons (H+) along the nanowire (NW).© 2010 Wile-VCH

One of the key components of a fuel cell, the proton-exchange membrane, is also the hardest part to design on a small scale. Rather than using an electrolyte solution for this purpose, Zhu and her co-workers previously fabricated nanowires of the synthetic polymer Nafion — an efficient proton conductor. However, they only succeeded in making nanowires 20 μm long, which is too short for building a fuel cell.

“We have now introduced a new method called ‘electrospinning’,” says Zhu. “With this method we can easily produce Nafion nanowires as long as centimeters. We can now build a fuel cell based on a single nanowire.”

In each fuel cell, a nanowire is mounted between two gold electrodes coated with different enzymes (see image). One of these enzymes catalyzes the oxidation of glucose, while the other catalyzes the reduction of dissolved oxygen. The combined redox reaction causes protons to flow from the anode to the cathode through the nanowire.

“A single-nanowire biofuel cell generates output power of up to 3 μW when placed in glucose solution, human blood or even watermelon juice,” says Zhu. She and her co-workers demonstrated that their cell could power a glucose sensor, a pH sensor and a light sensor.

“In addition to glucose sensors, which are very important for monitoring glucose levels in diabetes patients,” explains Zhu, “our technology could be used for other sensors such as blood pressure sensors and heart beat sensors. In our future research we hope to improve the output of the biofuel cell to a level that could allow it to be used to power a cardiac pacemaker.”