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?
Dr. Lee's paper will be available for free online for the next 30 days. Download of the paper requires free site registration at Institute of Physics’ Journal of Micromechanics and Microengineering.
Sorry Jamais, but we won't be seeing urine-powered paper batteries any time soon: if you read the paper closely, you see that urine simply releases the magnesium and copper chloride laminated within the paper, allowing an electrochemical reaction to take place. A cool trick, sure, but probably not useful for relief efforts.
Ben, thank you for the correction. I've made the appropriate changes to the post.
I still wonder whether this could be scaled beyond the trickle (ahem) voltage. It may not have real value for relief efforts, but might still be useful in emergency kits for (say) recharging a dead cell phone or powering a "here I am" beacon.
In the future, toddlers who take a tinkle at the wrong time will find themselves sternly corrected by their cybernetic talking training pants.
I would like to rescind my earlier statement that this could not be used for relief efforts. I think that the idea of this type of scalable paper battery would work well for integrating onto very small, very cheap micro total analysis systems (uTAS) for diagnosis of diseases in areas where doctors can't get to.
Imagine you have a bucket of diagnosis machines, for example a microfluidic cell and two electrodes, that you do capillary electrophoresis with and examine for tell-tale bands of junk/bugs. You still have to hook this up to a voltage supply and examine it under a microscope. If you can take away the hardware, you can drastically increase the amount of people that can use it.
If you can kick out the voltage supply, by patterning these pieces of paper for basically free, then you just have to figure out how you can indicate the result to the user. Cut yourself and let the blood flow over a credit-card, if an LED lights up, you've got Trypanosomiasis . . . or whatever. It is probably important to mention that although urine was used in this paper, you could probably use anything wet and salty.
Ben's last post reminded me of this:
The salts are already in the battery, so you could probably make it work with anything wet.