taking the pi** or what?

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    Inexpensive, easily-made medical sensors and disposable testing kits need inexpensive, easily-made power sources, but until now, these have been difficult to come by. "DNA Chip" type biosensors and the like don't need a lot of power, but do need some. With that in mind, a research team at Singapore’s Institute of Bioengineering and Nanotechnology led by Dr Ki Bang Lee has devised a cheap-to-make paper battery that uses the fluid being tested -- urine -- as a power catalyst.

    The battery unit is made from a layer of paper that is steeped in copper chloride (CuCl) and sandwiched between strips of magnesium and copper. This “sandwich” is then held in place by being laminated, which involves passing the battery unit between a pair of transparent plastic films through a heating roller at 120ºC. The final product has dimensions of 60 mm x 30 mm, and a thickness of just 1 mm (a little bit smaller than a credit card).
    Writing in the Journal of Micromechanics and Microengineering, Lee describes how the battery was created and quantifies its performance. Using 0.2 ml of urine, they generated a voltage of around 1.5 V with a corresponding maximum power of 1.5 mW. They also found that the battery performances (such as voltage, power or duration) may be designed or adjusted by changing the geometry or materials used.

    Notably, 0.2 ml urine allowed battery output for over 15 hours at a 10 ohm load, and a second 0.2 ml drop gave another 15 hours of runtime at roughly the same voltage output. Urine tests are widely used for medical diagnoses, as concentrations of various chemicals (such as glucose) can accurately reflect the body's health (this also might make drug testing via urinalysis more common, although this possibility was not discussed in the research). The question that comes of this (for me, at least) is how scalable the battery system might be. How much power could one get out of a typical day's urine output? Could an inexpensive "paper battery" be part of emergency kits -- "Just Add Pee" -- or useful in relief efforts?

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