Noninvasive Contact Lens Sensor Detects Tear Serotonin for Stress Assessment

Stress-related physiological changes can be difficult to monitor objectively over time. Serotonin plays a role in mood regulation and stress physiology and is also present in tears, providing a minimally invasive source of biochemical information. Building on this potential, researchers have developed a soft contact lens sensor that measures serotonin levels in tear fluid.

The Terasaki Institute for Biomedical Innovation (Los Angeles, CA, USA) developed the reusable lens as part of its Ocular Library for the Analysis of Tear Biomarkers (OCULAB) platform. A thin, flexible sensor is integrated into a standard soft contact lens. The sensor contains ferrocene, which reacts with serotonin to produce an electrical signal that can be converted into a concentration reading. The current laboratory-connected system requires tear samples to be collected and analyzed after the fact. 

The study examined whether a soft ocular device could detect serotonin in the small, changing volume of tear fluid. Published in Science Translational Medicine on September 16, 2026, the work found that the sensor detected concentrations as low as 72 picomolar. That sensitivity was approximately 200 times greater than needed to measure typical human tear serotonin concentrations. The lens maintained accurate readings across up to 400 uses over several days. 

In a mouse model of chronic stress, tear serotonin decreased while cortisol increased in both blood and tears. A pilot study also examined tear samples from 10 volunteers during a standardized stress test. Their serotonin levels fell during the stressful task and returned toward baseline afterward. 

The team plans to add wireless components so a future lens can acquire and transmit readings while worn. Larger, more diverse human studies are needed to establish how tear serotonin relates to stress and mental health across populations. Long-term stability, calibration, comfort, manufacturing reproducibility, and extended safety on the eye also remain to be established before clinical use.

“The eye provides a unique window into both ocular and systemic physiology. Through our ocular bioelectronics program, we are developing soft ocular devices that can turn the tear film into a source of longitudinal biochemical information. Serotonin is an important proof-of-concept target, but the broader goal is to build wearable ocular systems capable of monitoring multiple biomarkers and physiological signals over time,” said Dr. Yangzhi Zhu, principal investigator and assistant professor at the Terasaki Institute for Biomedical Innovation. 

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Terasaki Institute for Biomedical Innovation