Scientists at the California Institute of Technology (Caltech) have come up with a first-of-its-kind wearable skin sensor that has the potential to wirelessly detect the existence of CRP in human sweat. This sensor will make it simpler for patients and medical professionals to track their health without the requirement for highly invasive blood tests.
Wei Gao. Image Credit: California Institute of Technology
While inflammation is very familiar to us as redness, pain, and swelling, a slew of biochemical markers is linked to it as well.
One such marker, the C-reactive protein, otherwise called CRP, which is secreted by the liver, is so commonly linked to inflammation that its existence in the bloodstream is a powerful indicator of a basic health condition.
Wei Gao, whose lab is accountable for the development of a range of wearable sweat sensors, such as this latest one, says CRP is much harder to detect than the molecules detected by his other sweat sensors. One reason is that CRP is present in the blood at a much lower concentration compared to other biomarkers.
This is mostly because CRP molecules are much larger compared to other biomarker molecules, which implies it is highly hard for them to be secreted from the bloodstream into sweat. Generally, another reason is that sensitive CRP detection needs unique laboratory steps that wash samples to guarantee consistent sensing.
Those were the main issues that prevented people from doing wearable CRP sensing before. We need high sensitivity to monitor very low-concentration CRP automatically on the skin.
Wei Gao, Assistant Professor, Medical Engineering, California Institute of Technology
Gao is also a Heritage Medical Research Institute Investigator and Ronald and Joanne Willens Scholar.
This CRP sensor, like other sensors by Gao and his team, is constructed upon laser-engraved graphene, a sheet-like form of carbon. The graphene structure comprises several small pores that create a huge amount of surface area. Those pores are fixed with antibodies that fix CRP and unique molecules (redox molecules) capable of producing a small electric current under some conditions.
Also, the sensor comprises gold nanoparticles that carry with them an isolated set of CRP antibodies (detector antibodies).
When CRP molecules enter the sensor through sweat, they fix to both the detector antibodies on the gold nanoparticles and the antibodies on the graphene, temporarily gluing the nanoparticles to the graphene and activating the redox molecule to produce an electrical current that could be quantified by electronic components fixed to the sensor.
Since every gold nanoparticle comprises several detector antibodies, they amplify the minuscule signal that a single CRP molecule would offer differently.
To consider the impact of changes in sweat compositions from person to person on the electrochemical signal of the biosensor, the sensor was also developed to quantify the concentration of ions in the sweat, skin temperature, and sweat pH.
Gao states that the work illustrates initially that sweat CRP could be detected precisely and has a good correlation with its counterpart in blood, which has impacts on his work in the laboratory and practical medical applications.
This is a general platform that lets us monitor extremely low-level molecules in our body fluids. We hope to expand this platform to monitor other clinically relevant protein and hormone molecules.
Wei Gao, Assistant Professor of Medical Engineering, California Institute of Technology
Gao added, “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 co-authors of the study are medical engineering graduate students Jiaobing Tu (MS '20), Jihong Min (MS '19), Changhao Xu (MS '20), and Jiahong Li; postdoctoral scholar research associates in medical engineering Yu Song and Elham Davoodi; staff scientist Ting-Yu Wang and Tsui-Fen Chou, research professor of biology and biological engineering, all of Caltech; Jeff Moore and Harry B. Rossiter of the Lundquist Institute for Biomedical Innovation at Harbor-UCLA Medical Center; Justin Hanson, Erin Hu, and Jeffrey J. Hsu of UCLA; and Tanyalak Parimon and Peter Chen of the Women's Guild Lung Institute at Cedars-Sinai Medical Center.
The study was financially supported by the American Heart Association, the National Institutes of Health, the National Science Foundation, the Office of Naval Research, the Tobacco-Related Disease Research Program, a Sloan Research Fellowship, and the Technology Ventures Internal Project Fund at Cedars-Sinai.
Wearable Sensor Detects Internal Inflammation
Video Credit: California Institute of Technology
Journal Reference
Tu, J., et al. (2023) A wireless patch for the monitoring of C-reactive protein in sweat. Nature Biomedical Engineering. doi.org/10.1038/s41551-023-01059-5.