When I was 11-years-old, I could hardly finish a sentence without generating a small lake of saliva between my tongue and my plastic retainer. And, like any prepubescent with extreme, corrective mouth gear, I yearned for the day when I’d be able to wake up in the morning without a slick sheen of spit between my head and the pillow.
But little did I know then that I was actually generating a precious resource, something that could one day power small devices of the future. That’s because, instead of looking to large-scale renewable energy projects like giant solar installations in the desert, researchers are now hunting for fuel sources in the smallest, most common of places: Namely, your mouth.
Last month, a team of researchers from Penn State University and Saudi Arabia’s King Abdullah University of Science and Technology (KAUST) showed that it was possible to run a microbial fuel cell on saliva. The fuel cell, which used a highly conductive material called graphene and cost something in the range of $2 to $3, was able to turn the “organic content” of spit into approximately 1 microwatt of power.
If that sounds tiny, it is. Compared to something like a solar panel, a spitty microbial fuel cell is not a very dense kind of energy generation. But dense energy isn’t the goal. One microwatt of power, it turns out, would be enough to fuel small diagnostic tests on the battlefield or in rural areas that lack easy access to water and electricity. If produced on silicon, researchers say the device would cost 50 cents.
“To really make these kind of devices useable, you cannot just be depending on some hazardous waste material like acetate, which is traditionally being used,” explains KAUST professor Mohammad Mustafa Hussain. “Is there anything common that we can use, like in sub-Saharan Africa or a battlefield? That kind of motivated us.”
As another kind of example, Hussain asked me to think about my iPhone. Instead of carrying around a (relatively) bulky battery that drains fairly quickly, what if my business cards had tiny microbial fuel cells on one side? With a classier fuel cell design, I could simply hook up my phone to business cards I’ve drooled on.
Right now, Hussain and his team are working on expanding the fuel cell’s capabilities. If the first version was a sedan, he says, the one they’re currently working on is a Land Rover. It features three fuel cells connected to one another, which actually magnifies the energy density. All that’s needed is more spit.
Saliva isn’t the only material researchers are investigating. Hussain is also in the process of generating energy from used tea leaves and talking to Greek yogurt companies to see how he can leverage their waste stream. But when it comes to small devices powered by spit, the electrical engineer imagines a range of applications–everything from a diabetes test kit to a tiny fertility indicator.
“The philosophy behind this technical aspiration is to reach out and help the global population,” Hussain says. “We [electrical engineers] don’t always get an opportunity to do that when making the world’s fastest computer or the world’s smartest iPhone.”