Chemists build body fluid battery

Biofuel cell runs on metabolic energy to power medical implants.
12 November 2002
PHILIP BALL

Our bodies could one day power their own electronic implants. Chemists have developed a miniature battery that could run on bodily fluids to drive sensors to monitor our health.

The biofuel cell converts directly into electricity1 the energy produced when glucose reacts with oxygen during normal metabolism. It could be inserted in contact with glucose-containing body fluids under the skin or in the spinal cord, for example.

Batteries that run on biological fuels are not a new idea. Devices that generate power from the glucose-oxygen reaction were made almost 40 years ago. But to be medically useful, such cells need to be tiny, they must work at the temperature, acidity and salt concentration of blood, and must produce sufficient power and voltage. Adam Heller, of the University of Texas at Austin, and colleagues believe that their device fulfils these requirements.

It consists of two carbon fibres, 2 cm long and 7 thousandths of a millimetre wide, each coated with a catalyst that assists the chemical reactions of glucose burning. This reaction takes place in two halves, one at each electrode.

One electrode is coated with a polymer and an enzyme called glucose oxidase, which strips glucose of electrons. The polymer makes an electrical connection between the enzyme and the carbon fibre. At the other electrode, another polymer-wired enzyme adds electrons to dissolved oxygen. As the reaction proceeds, electrons are fed in a current around an electrical circuit.

The device works at a temperature and alkalinity close to those of normal blood: at 37 șC, and at pH 7.2. It produces about the same amount of power as a wristwatch battery: about 1.9 microwatts. It could drive a miniature glucose sensor for monitoring diabetics, Heller suggests.

But it couldn't power an artificial heart, he says. The device is too weak and too short-lived - currently it loses around 6% of its power per day. Rather, says Heller, such biofuel cells could be used as research tools, for example to power tracking devices attached to insects or animals over the course of a few days.

Moreover, real body fluids, like those between our cells, are more complicated than the model fluids that the researchers have used so far, and may introduce complications. "I very much expect that we will need to clean up the chemistry," says Heller, before biofuel cells can be put to use in medicine.

References
.Mano, N., Mao, F. & Heller, A. A miniature biofuel cell operating in a physiological buffer. Journal of the American Chemical Society, 124, 12962 - 12963, (2002). |Article|

© Nature News Service / Macmillan Magazines Ltd 2002




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