Saliva-powered micro-sized microbial fuel cells can produce minute amounts of energy sufficient to run on-chip applications, researchers said.
"There is a lot of organic stuff in saliva," said Bruce E Logan from the Pennsylvania State University who carried the study along fellow researcher Justine E Mink.
Microbial fuel cells create energy when bacteria break down organic material producing a charge that is transferred to the anode.
Logan, who has studied microbial fuel cells for more than ten years, usually looks to wastewater as a source for both the organic material and the bacteria to create either electricity or hydrogen, but these tiny machines are a bit different.
"By producing nearly 1 microwatt in power, this saliva-powered, micro-sized MFC already generates enough power to be directly used as an energy harvester in microelectronic applications," researchers said.
Researchers believe that the emergence of ultra-low-power chip-level biomedical electronics, devices able to operate at sub-microwatt power outputs, is becoming a reality.
One possible application would be a tiny ovulation predictor based on the conductivity of a woman's saliva, which changes five days before ovulation.
The device would measure the conductivity of the saliva and then use the saliva for power to send the reading to a nearby cell phone.
Biomedical devices using micro-sized microbial fuel cells would be portable and have their energy source available anywhere, researchers said.
In the past, the smallest fuel cells have been two-chambered, but this micro version uses a single chamber with a graphene - rather than platinum - coated carbon cloth anode and an air cathode.
The anode is actually composed of carbon nanomaterial graphene. Other microbial fuel cells used graphene oxide, but the researchers showed that pure multi-layered graphene can serve as a suitable anode material.
While the researchers tested this mini microbial fuel cell using acetate and human saliva, it can use any liquid with sufficient organic material.
The study was published in the Nature Publishing Group's journal Asia Materials.