A urine powered battery the size of a credit card has been invented by Singapore researchers.
A drop of urine generates 1.5 volts, the equivalent of one AA battery, says Dr Ki Bang Lee of the Institute of Bioengineering and Nanotechnology.
He says the technology could provide a disposable power source for electronic diagnostic devices that test urine and other body fluids for diseases like diabetes.
These currently need lithium batteries or external power sources. But with this system, the body fluid being tested could power the unit itself.
Lee, who reports the new battery in the latest Journal of Micromechanics and Microengineering, says a smaller version could potentially power mobile phones in emergencies.
How does it work ?
The battery is made of a layer of filter paper steeped in copper chloride sandwiched between strips of magnesium and copper, then laminated in plastic.
It’s activated when a drop of urine is placed on the battery. The urine soaks through the paper providing the necessary conditions to generate electricity.
The magnesium acts as the battery’s anode, shedding its electrons, while the copper chloride acts as the cathode, gathering them up.
This electron flow delivers power greater than 1.5 milliwatts, the researchers say.
CSIRO research physicist Dr Cathy Foley says the research is important because it raises the possibility of having a self-powered device.
She says the technology could be used in what are known as biomicroelectromechanical systems, or bioMEMS.
Examples of bioMEMs include nanomachines that seek out and destroy cancer cells or cholesterol, or DNA chips with DNA as electronic components.
The technology could also be used to power drug-testing kits, she says.
Foley says the concept could work using any body fluid including semen, blood or tears, as long as the fluid isn’t neutral at pH 7.
Urine, for instance, has a range of pH 4.5 to 8.0, according to the Royal College of Pathologists of Australasia.
Is it practical?
Foley says the energy generated by the urine-powered battery would be enough to keep a digital wristwatch or a scientific calculator going, but anything bigger would be impractical.
"You could probably increase the power by having more of them and loading them up," she says.
"For power on a large scale you’d probably have to coat the whole of Australia in this paper-based electrode and wee on it."