Contact Lens Measures Serotonin in Tears for Stress Monitoring

New Wearable for Stress Monitoring

A new study introduces a "lab on a contact lens" capable of measuring the neurotransmitter serotonin in tears. This development provides a potential wearable method for non-invasively analyzing stress levels.

Yangzhi Zhu, director of the biomedical device center at the Terasaki Institute for Biomedical Innovation, stated that tears could become a practical, noninvasive source of biochemical information. This allows for repeated measurements over time, unlike current methods that provide only snapshots.

Addressing Limitations of Current Stress Assessment

Stress is linked to various disorders, including depression and schizophrenia. Current methods for measuring stress, such as questionnaires or diaries, are subjective and complicate accurate evaluations. The researchers aimed to create an objective device for stress assessment by measuring serotonin.

Serotonin, a mood-regulating hormone, is found in small amounts in tears. The challenge was to develop a sensor sensitive enough to detect these low concentrations and distinguish serotonin from other molecules in tears.

Smart Contact Lens Development

Zhu and his team fabricated soft, reusable hydrogel lenses. These lenses encapsulate flexible biocompatible graphene and silver electrodes printed in serpentine patterns, designed to withstand repeated deformation. Ferrocene was bonded to the graphene to aid in strong and repeatable serotonin detection.

Performance and Sensitivity

The smart contact lenses were tested in lab dishes using artificial tears laced with serotonin. The lenses demonstrated the ability to detect serotonin concentrations as low as 72-trillionths of a mole per liter, which is below the average human tear serotonin concentration of approximately 15-billionths of a mole per liter.

Experiments also showed the lenses maintained functionality for over 28 days despite repeated flipping, folding, stretching, and twisting.