You're looking at a photo of the world's first urine-powered battery, invented by Korean scientist Ki Bang Lee. Why might you want one? To simplify, potentially, a variety of common diagnostic tests, he says, and one day make it easier for patients to monitor medical conditions at home.

Made of paper that is saturated in copper chloride and sandwiched between strips of magnesium and copper chloride, the device generates an electrical charge equal to that of an AA battery (1.5 volts) when put in contact with just one drop of urine.

As in a conventional battery, the power comes from a chemical reaction, explained a recent article in the Journal of Micromechanics and Micro-engineering. In this case, substances in the urine produce a flow of electrons from the magnesium (the anode) to the copper chloride (the cathode).

Lee foresees use of the device together with specific biochips to create convenient, cheap and disposable diagnostic kits to test, for example, glucose levels in people with diabetes or to detect food or water poisoning. The patient's urine would both furnish needed information and power the chip. Lee says his battery will also work with saliva or blood, but he considers urine more convenient, in terms of supply and ease of collection. Basically, it's just a trip to the bathroom, and no one gets hurt.

-- Ranit Mishori

Copper Layer