Researchers at the California Institute of Technology (Caltech) have established a new graphene-based stress sensor that can monitor the body’s level of the stress hormone cortisol.
The innovation could potentially be used by NASA to measure the anxiety levels of its astronauts, as well as being developed for use in monitoring and treating a range of health issues, such as depression and post-traumatic stress disorder (PTSD).
A Non-Invasive and Quantitative Measurement of Cortisol
Stress is a physiological response that plays an important factor in many psychological states, as well as contributing to physical illness. However, while the effects of stress are biological, tests that have been widely used to measure stress have mostly relied on subjective reports on the perceived levels of stress. At present, the only established method of generating quantitative data on stress levels is to measure the levels of cortisol in the blood. However, this method requires drawing blood, which often causes peaks in stress levels due to the invasive procedure, which can skew results.
An assistant professor at Caltech has innovated a wireless sweat sensor that overcomes the limitations of the blood test method as it accurately measures levels of cortisol without the invasiveness of a needle. In a paper published last month in the journal Matter, scientist Wei Gao and his team describe how they developed a device that is both portable and able to be mass-produced, they also demonstrate how it is effective at measuring levels of cortisol in near real-time.
Previously, Gao had developed a sweat sensor for measuring the levels of uric acid in the bloodstream – a device that has applications in the management of illnesses such as cardiovascular disease, diabetes, or kidney disease. Gao used this work as a starting point, using a similar approach to create the new graphene-based sweat sensor for measuring cortisol.
To create these sensors, a laser is used to etch a 3D graphene structure on to the surface of a plastic sheet which incorporates tiny pores to allow small amounts of sweat to enter the sensor for analysis. The large number of these tiny pores adds up to create a large surface area of the sensor, making it sensitive enough to pick up on the numerous compounds existent in sweat. In the cortisol sensor, a cortisol-sensitive antibody is coupled with the tiny pores, allowing the sensor to recognize the presence of the hormone in the sweat.
The team tested the efficacy of the sensor in two different experiments. In the first, the researchers analyzed a volunteer's sweat over six days. The data collected demonstrated the daily rise and fall of cortisol levels in a healthy individual. Previous studies have determined that the regular cycle of cortisol peaks just after waking and declines throughout the day, this is the cycle that the sensor picked up on, demonstrating its effectiveness. This ability to monitor daily fluctuations of the hormone, Gao says, will lend it to being used in applications to indicate the presence of mental health conditions, such as depression which is marked by elevated cortisol levels.
In the second experiment, the sensor was used to detect changes in cortisol levels in response to acute stressors, such as intense exercise and the submergence of the participant’s hand in icy water. The results showed the sensor’s success is detecting augmentations in cortisol immediately.
Applications From Monitoring Astronaut’s Stress Levels To Detecting Mental Health Issues
What the Caltech team has achieved is the establishment of a cost-effective, portable, non-invasive and accurate sensor that can reliably monitor stress levels in near real-time. This will allow for the easier and more widespread monitoring of conditions such as anxiety, depression, and PTSD. In addition, Gao has been selected as one of six researchers who will participate in studies investigating human health during deep-space missions. He will be developing his sensor for use in gauging the stress and anxiety levels of the astronauts involved in the program.