Smart contact lens detects serotonin changes in tear samples collected during stress test

A team led by Dr. Yangzhi Zhu from the Terasaki Institute for Biomedical Innovation has developed a soft, reusable smart contact lens that can detect serotonin levels in tear samples. This innovation, part of their Ocular Library for the Analysis of Tear Biomarkers platform, aims to provide noninvasive, longitudinal biochemical monitoring through the ocular surface and tear film.

Serotonin, an important signaling molecule linked to mood regulation and stress-related physiology, is present in tears, making them an attractive source of biochemical information. The lab-on-a-contact-lens device integrates a thin, flexible sensor using ferrocene, a compound that reacts with serotonin to generate an electrical signal.

This sensor is capable of detecting serotonin at concentrations as low as 72 picomolar, making it 200 times more sensitive than needed to measure typical human tear serotonin levels. In a mouse model of chronic stress, tear serotonin levels decreased while cortisol, a known stress hormone, increased in both blood and tears, mirroring patterns observed in prior human stress research.

A small pilot study with 10 volunteers during a standardized stress test showed similar results, with serotonin levels falling during the stressful task and returning to baseline afterward. The lens demonstrated accuracy across up to 400 uses over several days, indicating potential for reuse rather than replacement after each measurement.

Dr. Minwoo Kim, the study's first author, emphasized that the lens allows for reading physiological information without needles or lab visits, utilizing a feature already present in daily use - the contact lens. Dr. Zhu, the principal investigator, noted that the eye offers a unique window into both ocular and systemic physiology, and their ocular bioelectronics program aims to create soft ocular devices capable of transforming the tear film into a source of longitudinal biochemical information.

The team's next step is to develop a fully integrated wearable system with wireless capabilities, enabling real-time acquisition and transmission of readings while the lens is being worn. Further human studies are required to establish how tear serotonin relates to stress and mental health across different populations, and to ensure long-term sensor stability, calibration, comfort, manufacturing reproducibility, and safety before clinical application.