Smart contact lens detects stress from tears. Scientists have already successfully tested it

How stressed are you? In the future, we might not look for this answer using smartwatches or questionnaires, but with an elegant chemical solution. A team from the American Terasaki Institute has embedded a sensor into the edge of a soft contact lens that detects serotonin in tears, which is involved in mood regulation. According to a study in Science Translational Medicine, it could one day monitor changes in the body without a single blood draw.

How can a contact lens detect stress?

The whole idea is based on a simple chain. The lacrimal gland produces tears from blood plasma, so serotonin, which circulates in the blood, also gets into them in a smaller concentration. When a person is under stress, the body produces less of it in the digestive tract. Less serotonin in the blood should therefore also manifest in tears.

The results were published on September 16 by the scientific journal Science Translational Medicine, a sister publication to the prestigious Science magazine. Since then, the study has been cited by foreign websites Earth.com and IEEE Spectrum, to whom lead researcher Yangzhi Zhu spoke about the details. He himself, however, tempers exaggerated expectations. “I would be cautious about claiming that serotonin in tears directly tracks stress one-to-one. We observed that it changed in our models under conditions associated with stress,” he told Earth.com.

Electronics are hidden on the edge of the lens

Scientists printed three tiny graphene and silver electrodes onto the hydrogel lens. They run in waves along its edge, so they don’t obstruct vision and can withstand repeated bending. Another layer covers them, leaving only a small opening for tears. The entire lens measures approximately 300 micrometers, which is about three sheets of paper, and according to the authors, the electronics add less than a tenth of its thickness.

In the lab with artificial tears, the sensor detected serotonin even at a concentration about two hundred times lower than what tears normally contain. It provided a response in less than 40 seconds and remained functional after more than four weeks of flipping, folding, stretching, and twisting. This combination, according to the authors, is the most difficult, as such sensitive sensors tend to be rigid.

Who has already tested the lens?

First, mice were tested. Five of them underwent two weeks of daily stress, while another five lived normally. The stressed animals had more stress hormone cortisol and less serotonin in both their blood and tears. For cortisol, the values from both fluids matched almost exactly; for serotonin, the correlation was weaker but still statistically significant.

On a living eye, the lens has only been tested on a sedated pig so far. Scientists placed the lens on its eye for about five minutes and dripped artificial tears with a known amount of serotonin into the eye, and the lens detected every change. An eye examination after removal revealed no inflammation or irritation.

Ten volunteers participated in the pilot phase, undergoing a standard laboratory stress test involving a short speech and mental arithmetic before two evaluators. Scientists collected their tears before the test, during it, and after rest, and then measured them with the lens in the lab. Serotonin decreased during stress and returned to baseline after rest. However, none of the volunteers wore the lens on their eye.

Smart contact lens detects stress from tears. Scientists have already successfully tested it Adam Kurfürst News Adam Kurfürst News

Today’s smartwatches and rings, such as the recently introduced Casio ring, primarily measure heart rate, temperature, or blood oxygenation. According to Professor Wei Gao from the California Institute of Technology, who was not involved in the research, the work points towards a direction from physical signals to continuous molecular monitoring. “The eye and tears are an interesting interface because they could allow for repeated biochemical measurements without blood draws,” he told IEEE Spectrum.

When could the smart lens reach people?

During tests, the lens was connected to laboratory instruments with thin nickel wires. However, the team has already assembled a wireless version with an NFC chip, which operates without a battery, draws power from a nearby phone, and also sends data to it. Even this version, according to the authors, needs further refinement and safety tests. Zhu mentioned that the lens could also be produced in a prescription version.

Before anyone could wear it all day, Zhu says it will require larger human studies, long-term eye tolerability tests, stable calibration, and a fully wireless system. In the future, the team aims to measure more substances simultaneously to give the lens a more comprehensive picture of the body’s condition. No mention has been made yet of a timeline or a commercial product.

Would you wear a contact lens that monitors your stress levels?

Sources: Earth.com, IEEE Spectrum