Wearable noninvasive sensor monitors sweat for signs of inflammation
Researchers have developed a wearable, noninvasive sensor that monitors for a biomarker of inflammation in the wearer’s sweat. They say the device could be used at home by people with chronic inflammatory diseases.
Inflammation is associated with a range of mental and physical disorders, including the top three biggest killers worldwide: ischemic heart disease, stroke, and chronic obstructive pulmonary disease (COPD).
Whereas the acute inflammatory response is the body’s natural way of fighting infection and speeding up healing, long-term or chronic inflammation can lead to irreversible tissue damage. Being able to quickly and easily detect inflammation is key to its treatment. Measuring the levels of C-reactive protein (CRP) in the blood is commonly used as a biomarker of inflammation but requires complex lab equipment and personnel to analyze the blood sample.
Now, researchers from the California Institute of Technology, Caltech, have developed a novel wearable sensor, called the InflaStat, that wirelessly and noninvasively monitors inflammation by measuring CRP levels in human sweat.
The researchers had to overcome some obstacles before embarking on making their first-of-its-kind sweat-analyzing sensor. The main one is that CRP is more difficult to detect than other molecules. It’s present in the blood in much lower concentrations than other biomarkers, and its molecules are much larger, meaning that secreting them from the bloodstream into sweat is harder.
“Those were the main issues that prevented people from doing wearable CRP sensing before,” said Wei Gao, corresponding author of the study. “We need high sensitivity to monitor very low-concentration CRP automatically on the skin.”
The InflaStat is made from laser-engraved graphene containing tiny pores that create a large surface area. The pores contain antibodies that bind with CRP and special molecules called redox molecules capable of generating a small electric current under certain conditions. Incorporated into the sensor’s structure are gold nanoparticles, each of which carries a separate set of CRP-detecting antibodies.
When CRP molecules from the wearer’s sweat enter the sensor they attach to both the detector antibodies and the antibodies in the graphene pores. The nanoparticles then attach to the graphene and trigger the redox molecules to generate an electrical current that is read by the electronic components attached to the sensor.
Because each gold nanoparticle contains many detector antibodies, the signal – which is very small – is amplified far more than the signal a single CRP molecule would produce.
The researchers tested the InflaStat on healthy participants, patients with COPD and participants who’d recovered from a COVID infection. They found that the sensor was comfortable to wear and could obtain inflammatory biomarker information noninvasively and wirelessly. The data was displayed on a custom smartphone app in real-time. As expected, CRP levels in patients with COPD and those post-COVID infection were substantially higher than in healthy participants. The researchers found that the sensor accurately detected sweat CRP levels which correlated with blood levels.
The researchers say that their study’s findings demonstrate that their sensor could be used for noninvasive, at-home monitoring of chronic diseases like inflammatory bowel disease or COPD. What’s more, they say it could be adapted to test for other trace-level and disease-relevant biomarkers.
“This is a general platform that lets us monitor extremely low-level molecules in our body fluids,” Gao said. “We hope to expand this platform to monitor other clinically relevant protein and hormone molecules. We also want to see if this can be used for chronic disease management. Inflammation means a risk for many patients. If they could be monitored at home, their risk can be identified, and they can be given timely treatment.”
The study was published in the journal Nature Biomedical Engineering and the below video, produced by Caltech, shows how the sensor works to detect CRP.