In a recent article published in the journal npj Flexible Electronics, researchers presented a new approach for monitoring psychological stress through a flexible wearable sensor capable of detecting cortisol levels in sweat. This research aims to address these limitations by developing a user-friendly device that provides accurate and immediate feedback on cortisol concentrations, thereby facilitating better management of stress-related conditions.
A Bare carbon electrode under SEM. B The pyrrole deposited electrode under SEM. C SEM of the electrodes after elution of cortisol from MIP. D Physical image of laboratory cortisol test. E CV comparison between a normal carbon electrode and deposited CNT. F CV before and after cortisol binding. Image Credit: https://www.nature.com/articles/s41528-024-00333-z
Background
Cortisol, a steroid hormone released in response to stress, plays a crucial role in the body’s physiological response to various stimuli. Its levels fluctuate throughout the day and can be influenced by factors such as physical activity, emotional state, and environmental conditions. The traditional methods for measuring cortisol, including blood tests and saliva samples, are often invasive and time-consuming.
Recent advancements in wearable technology have opened new avenues for non-invasive monitoring of physiological markers, particularly through sweat analysis. The integration of flexible materials and innovative sensing technologies has made it possible to create devices that can continuously monitor cortisol levels in real-time. This research builds on previous studies that have explored the dynamics of cortisol release in response to stressors, such as cold exposure, and aims to develop a practical solution for everyday use.
The Current Study
The sensor was constructed using a flexible substrate made from styrene-ethylene-butylene-styrene (SEBS). It was chosen for its excellent mechanical properties and biocompatibility, which make it suitable for prolonged skin contact. The fabrication process began with the preparation of a molecularly imprinted polymer (MIP) specifically designed to bind cortisol selectively. This was achieved by polymerizing a mixture of functional monomers and cross-linkers in the presence of cortisol as the template molecule.
Carbon nanotubes (CNTs) were incorporated into the electrode design to enhance the sensor's electrochemical performance. The CNTs significantly increased the electrode's surface area, thereby improving its sensitivity to cortisol detection. The electrodes were then subjected to electrochemical characterization using cyclic voltammetry (CV) to assess their redox behavior before and after cortisol binding. The CV measurements were conducted in a phosphate-buffered saline (PBS) solution, which served as the electrolyte, allowing for the evaluation of the sensor's performance in a controlled environment.
The sensor's ability to detect cortisol in sweat was further validated through a series of experiments involving human subjects. To induce cortisol release, participants were subjected to an ice-water stimulation protocol, which is known to elicit a physiological stress response. Sweat samples were collected from the skin surface using the porous chitosan hydrogel (PCSH) integrated into the sensor design.
The PCSH was engineered to absorb sweat effectively, with an 80 % swelling rate that facilitated the collection of sweat while minimizing contamination from other biological fluids. Once the sweat was absorbed, the MIP within the sensor interacted specifically with the cortisol present in the sample, allowing for the electrochemical detection of cortisol levels.
Data acquisition was performed using an integrated circuit board that included an analog-to-digital converter (ADC) for current measurement. The sensor was powered by a rechargeable lithium polymer battery, ensuring portability and ease of use. Data transmission was facilitated through a Bluetooth 4.0 module, allowing for seamless communication with mobile devices for real-time monitoring and analysis.
Results and Discussion
The results demonstrated that the SEBS-based sensor exhibited high sensitivity and specificity in detecting cortisol concentrations. The electrochemical measurements revealed distinct redox peaks before and after cortisol binding, indicating the sensor's capability to accurately monitor changes in cortisol levels. The comparative analysis between SEBS and PET substrates showed that the SEBS substrate maintained excellent detection performance, reinforcing its suitability for wearable applications.
The experiments involving ice water stimulation confirmed that cortisol levels in sweat significantly increased in response to the stressor, peaking within 10 to 15 minutes before gradually returning to baseline levels. This dynamic response highlights the sensor's potential for real-time monitoring of physiological changes associated with stress.
The study also emphasized the importance of user-friendly design and rapid sample processing, which are critical for the practical application of wearable sensors in everyday life. The integration of MIP technology further enhanced the sensor's performance, providing a new way of continuously monitoring cortisol levels. The findings suggest that this wearable device could play a vital role in personalized health management, particularly in the context of mental health, where timely feedback on stress levels can inform interventions and lifestyle adjustments.
Conclusion
In conclusion, the research presents a significant advancement in the field of wearable technology for mental health monitoring. The high sensitivity and specificity of the SEBS-based sensor, combined with its user-friendly design, position it as a valuable tool for individuals seeking to manage their stress levels effectively. Future research could explore the integration of this technology into broader health monitoring systems, potentially enhancing our understanding of the relationship between stress and overall well-being.
Journal Reference
Wang C., Wang Z., et al. (2024). High-precision flexible sweat self-collection sensor for mental stress evaluation. npj Flexible Electronics 8, 47. DOI: 10.1038/s41528-024-00333-z, https://www.nature.com/articles/s41528-024-00333-z