Scientists Discover Protein in Human Tears Can Create Electricity

Scientists in Ireland have discovered that a protein found in tears, saliva, and egg whites can generate electricity. The protein, called lysozyme, can produce a small electrical charge when pressure is applied to it.

The findings, published October 2 in the journal Applied Physics Letters, could make waves in the world of medicine, where a biological material could now be used as an energy source for pacemakers and other biomedical devices just by applying pressure, a phenomenon called piezoelectricity.

Aimee Stapleton, a postgraduate fellow at Bernal Institute and the lead author on the study tells Inverse it will take take to turn this discovery into working tech, but the outcomes could be a big deal for anyone who relies on a biomedical device.

“If you could power it with a piezoelectric material,” she says, “then you wouldn’t need to replace the battery.”

Lysozyme is an antimicrobial protein that animals produce. It’s actually already a common food additive because of its antibacterial properties, and this new research could unlock even more dramatic applications.

Lysozyme has an innate antibacterial property, as its main role is to protect against infection by breaking down bacterial cells. While many other known piezoelectric materials contain toxic elements like lead, Stapleton says lysozyme’s nontoxic, organic quality could make it useful to biomedical technology.

In the future, a medical device that requires energy, like a pacemaker — which currently needs a battery — could be powered by a piezoelectric material. The vibrations of the heart could press on a piezoelectric protein, for example, and it would respond by generating an electrical charge that would power the pacemaker. Batteries would be a thing of the past.

For her research, Stapleton started with lysozyme as a powder, and changing it into a solution, she dropped it onto an electrode. As it dried, the lysozyme crystallized and Stapleton placed another electrode on top, squeezing the crystals.

“I was interested in lysozyme because it can be crystallized really easily, which makes it easier to study,” she says, “because crystallized structures tend to show piezoelectricity.”

What she discovered was that the lysozyme emitted a charge, which she could then measure using the electrodes. The charge, she says, was greater than what’s usually found in quartz, another common piezoelectric material.

“If we take a material like quartz, it gives a piezoelectric coefficient of two picocoulombs per newton, and we’re seeing with our protein crystals that we can get as large as 60 picocoulombs per newton,” she says.

Without worrying too much about the specifics of the measurements, that’s quite a bit more than quartz, which is already used extensively for its piezoelectric properties.

As exciting as this sounds, we don’t worry about the scientists of tomorrow trying to harvest the world’s tears to make it happen. Stapleton says that lysozyme is already a commonly used protein, most often acquired from hen egg whites. “I’m not going to go around making people cry to collect my lysozyme,” she says.