Whether you know it or not, we are in the Age of the Biosensor. These are small, cheap, disposable devices that can be used for a quick check for everything from the HIV virus to food-borne bacteria, to water contamination on the spot from a pinprick-size sample. And, they’re made of paper.
Paper batteries are perfect for the developing world, where complex equipment and people trained to use it are in short supply. Or they would be if they were self-powered. Paper biosensors don’t need pumps because the paper wicks up liquids, but the sensors do need to be used with hand-held devices to analyze the data.
In a major step toward a completely self-contained and automatic biosensor, Binghamton University engineer Seokheun “Sean” Choi has created a battery capable of powering the device made from folded paper and a drop of filthy water. The paper does have liquid nickel sprayed on one side, but the real secret ingredient is germs – anaerobic bacteria, to be precise, and there are millions of them in a drop of mud.
“Any type of organic material can be the source of bacteria for the bacterial metabolism,” Choi explained. Here’s how it works: every living thing breathes as part of the process of turning food into the energy our cells need to operate. The process yields extra electrons, which we air breathers attach to oxygen and produce water. Scientists discovered that some bacteria living in oxygen-free environments (like mud) can shed the electrons directly into their surroundings.
Using actual techniques of origami, the Japanese art of paper-folding, a battery able to run a biosensor in the field can fold down to the size of a matchbook. Choi’s invention doesn't require engineered nano materials like other paper-based batteries and nickel makes a cheap air-breathing cathode.
Photo of Paper Battery Courtesy of Martha Terry / Binghamton University.
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