Early disease detection depends on the rapid, continuous and convenient monitoring of vital biomarkers. Typically, monitoring biomarkers—chemicals in blood or other body fluids that indicate cellular or organismal states—requires the analysis of biofluids such as blood, urine, and sweat. These traditional methods are effective but not without drawbacks: blood tests are invasive and inconvenient; urine analysis lacks real-time capability and can be cumbersome; and while sweat analysis is non-invasive, it often requires the uncomfortable use of drugs to induce sweat, particularly in non-active individuals. These challenges can hinder the early diagnosis and management of diseases. A novel category of health indicators, known as solid-state epidermal biomarkers (SEBs), which are found in the skin's outermost layer, the stratum corneum, and include substances like cholesterol and lactate, shows promise. These biomarkers correlate strongly with conditions like cardiovascular disease and diabetes, but direct detection has traditionally been challenging due to the lack of effective charge transport pathways in solid electrodes for electrochemical sensing of SEBs.

Now, a breakthrough has been achieved by researchers at the National University of Singapore (NUS, Singapore) and the Agency for Science, Technology and Research (A*STAR, Singapore) with the development of a new sensor that allows for the continuous and real-time monitoring of SEBs directly on the skin. This sensor employs a non-invasive method to measure health indicators such as cholesterol and lactate by having SEBs dissolve into an ionic conductive hydrogel (ICH) layer on the skin, diffuse through the hydrogel matrix, and undergo electrochemical reactions catalyzed by enzymes at the interface with an electronically conductive hydrogel (ECH) layer. The sensor then wirelessly transmits relevant physiological data to an external user interface via a flexible printed circuit board, ensuring continuous monitoring.

This wearable, stretchable, hydrogel-based sensor overcomes the limitations associated with the traditional reliance on biofluid samples. The team’s findings published in the journal Nature Materials suggest that the sensor holds significant potential for widespread application in wearable health monitoring, enabling early detection of serious health conditions like cardiovascular diseases and stroke. It can also be utilized in chronic disease management, population-wide health screening, remote patient monitoring, and sports physiology. Additionally, the sensor is manufactured using a scalable, cost-effective screen printing process, enhancing its practicality for broader use.

“Our novel hydrogel sensor technology is key to enabling the non-invasive detection of solid-state biomarkers on skin,” said Assistant Professor Liu Yuxin from the NUS Institute for Health Innovation & Technology. “The ionic conductive hydrogel layer that solvates the biomarkers and the electronically conductive hydrogel layer facilitates electron transport. This bilayer enables the sequential solvation, diffusion and electrochemical reaction of the biomarkers. Another highlight is the sensor’s sensitivity with biomarkers being detected precisely even in low amounts.”

“This wearable sensor is the first-in-the-world that can monitor biomarkers on dry or non-sweaty skin,” added Dr. Yang Le, Principal Scientist and Head of the Sensors and Flexible Electronics Department of A*STAR’s IMRE. “The sensor’s novel bilayer hydrogel electrode interacts with and detects biomarkers on our skin, allowing them to become a new class of health indicators. The stretchable design enhances comfort and accuracy as well, by adapting to our skin’s natural elasticity. This innovation can change the way we approach health and lifestyle monitoring, particularly for those living with chronic conditions requiring constant health monitoring.” 

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