Lab on a Contact Lens Can Measure Stress Through Serotonin

Researchers developed a soft hydrogel contact lens embedding flexible, biocompatible graphene and silver electrodes printed in serpentine patterns, with ferrocene chemically attached to the graphene to enable electrochemical detection of serotonin in tears. In laboratory tests the lens detected serotonin down to about 72 picomolar, far below average human tear concentrations (~15 nanomolar), and remained functional after more than 28 days of repeated folding and stretching. The device measured decreases in tear serotonin from samples taken from 10 volunteers before and after stress tasks (public speaking and math), detected 50-100 nanomolar serotonin on an anesthetized pig eye without causing irritation, and operated with wired readout; the team also demonstrated a proof-of-concept battery-free wireless version using an NFC chip and stretchable antenna for smartphone-based data transfer.

The work positions tear fluid as a noninvasive, repeatable window into biochemical stress markers, offering complementary information to cortisol (short-term responses) by reflecting longer-term, mood-related serotonin dynamics. Parallel mouse experiments showed similar serotonin drops in blood and tears under imposed stress, suggesting tears can mirror systemic changes, but researchers note the need for broader validation across individuals, times of day, ocular conditions, and safety testing before clinical use. The group aims to expand the platform to measure multiple molecules simultaneously; the findings are reported in Science Translational Medicine.